Bulletin u ILLIN-OIS raiturail History Surv-ey BXILLETIN- An Urban Epiphytotic Of Phloem Necrosis and Dutch Elm Disease, 1944-1972 Cedric Carter bile Rogers Carter HATURAl HISTORY SUWEV AUG 13 1974 LIBRARy I'E OF ILLINOIS ^ARTMENT OF REGISTRATION AND EDUCATION >TURAL HISTORY SURVEY DIVISION BANA, ILLINOIS THE LIBRARY OF THE f\UG 9 1974 „. ,rY OF ILLINOIS ^?URBANA-CHAMPA.GN VOLUME 31, ARTICLE MAY, 1974 ILLIN^OIS iraiturail History Suz'-vey An Urban Epiphytotic Of Phloem Necrosis and Dutch Elm Disease, 1944-1972 1dric Carter iiile Rogers Carter >1 OF ILLINOIS FkRTMENT OF REGISTRATION AND EDUCATION VURAL HISTORY SURVEY DIVISION liANA, ILLINOIS VOLUME 31, ARTICLE 4 MAY, 1974 STATE OF ILLINOIS DEPARTMtlNT OF REGISTRATION AND EDUCATION BOARD OF NATURAL RESOURCES AND CONSERVATION DEiN Babbinqeb, Ph.D., Chairman; Thomas PiRK, Ph.D., Biology: h. L. Si.oss, Ph.D., neology; Herbert S. GUTOWSKV, Ph.D., Chemistry; Robert H. Andebson, B.S.C.E.. Engineering : Charles E. 0l.msted, Ph.D., Forexiry; W. L. Evebitt, E.E., Ph.D., Re-presenting the President of the University of Illinois; Elbert H. Haolev, Ph.D., Representing the President of Southern Illinois University. NATURAL HISTORY SURVEY DIVISION, Urbana, Illinois SCIENTIFIC AND TECHNICAL STAFF George Sprugel, Jr., Ph.D., Chief Alice K. Adams, Secretary to the Chief Section of Economic Entomology William H. Luckmann, Ph.D., Entomologist and Head Willis N. Bruce, Ph.D., Entomologist Wayne L. Howe, Ph.D., Entomologist Stevenson Moobe, III, Ph.D., Entomologist, Extension Howard B. Petty, Ph.D., Entomologist, Extension James E. Appleby, Ph.D., Associate Entomologist Edward J. Armbrust, Ph.D., Associate Entomologist Marcos Kogan, Ph.D., Associate Entomologist Joseph V. Maddox, Ph.D., Associate Entomologist Ronald H. Meyer, Ph.D., Associate Entomologist Robert D. Pausch, Ph.D., Associate Entomologist Ralph E. Sechriest, Ph.D., Associate Entomologist John K. Bouseman, M.S., Assistant Entomologist George L. Godfrey, Ph.D., Assistant Entomologist William G. Ruesink, Ph.D., Assistant Entomologist James R. Sanborn, Ph.D., Assistant Entomologist Douglas K. Sell, Ph.D., Assistant Entomologist Clarence E. White, B.S., Assistant Entomologist Keun S. Park, M.S., Assistant Chemist Sue E. Watkins, Supervisory Assistant Donald E. Kuhlman, Ph.D., Assistant Professor, Exten- RoscOE Randell, Ph.D., Assistant Professor, Extension TiM CoOLEY, M.A., Assistant Specialist, Extension John F. Walt, M.S., Assistant Specialist, Extension Jean G. Wilson, B.A., Supervisory Assistant Daniel P. Bartell, Ph.D., Research Associate Martha P. Nichols, M.S., Research Associate Susan Bond, B.S., Research Assistant Stephen D. Cowan, B.S., Research Assistant Stephen K. Evrard. B.S., Research Assistant Barbara J. Ford, M.A., Research Assistant Raymond A. Kotek, M.Mus., Research Assistant Rose Ann Megcoli, B.S., Research Assistant Barbara E. Peterson, B.S., Research Assistant Annemarie Redborg, B.S., Research Assistant Keturah Reinbold, M.S., Research Assistant Stephen Roberts, B.S., Junior Professional Scientist John T. Shaw, B.S., Junior Professional Scientist Lowell Davis, Technical Assistant Charles G. Helm, M.S., Technical Assistant Linda Isenhower, Technical Assistant Lu-PiNG Lee, M.S., Technical Assistaiit Section of Botany and Plant Pathology J. Cedric Carter, Ph.D., Plant Pathologist and Head Robert A. Evers, Ph.D., Botanist Junius L. Forsberg, Ph.D., Plant Pathologist Eugene B. Himelick, Ph.D., Plant Pathologist R. Dax Neely, Ph.D., Plant Pathologist D. F. Schoeneweiss, Ph.D., Plant Pathologist J. Leland Crane, Ph.D., Associate Mycologist Walter Hartstirn, Ph.D., Assistant Plant Pathologist Betty S. Nelson, Junior Professional Scientist Gene E. Reid, Technical Assistant Section of Aquatic Biology D. Homer Buck, Ph.D., Aquatic Biologist R. Weldon Larimore, Ph.D., Aquatic Biologist Robert C. Hiltibran, Ph.D., Biochemist William F. Childers, Ph.D., Associate Aquatic Biolo- gist Allison Brigham, Ph.D., Assistant Aquatic Biologist Warren U. Brigham, Ph.D., Assistant Aquatic Biologist Richard E. Sparks, Ph.D., Assistant Aquatic Biologist John Tranquilli, M.S., Assistant Aquatic Biologist Donald W. Dufford, M.S., Junior Professional Scientist Mary Frances Martin. Junior Professional Scientist John M. McNurney, M.S., Junior Professional Scientist CONSULTANTS AND RESEARCH AFFILIATES: Systematic Entomology. Roderick R. Irwin. Chicago, Illi- nois; Wildlife Research, Willard D. Klimstra, Ph.D., Professor of Zoology and Director of Cooperative Wild- life Research, Southern Illinois University ; Parasitology, Normak D. Levine, Ph.D., Professor of Veterinary Parasitology, Veterinary Research and Zoology and Director of the Center for Human Ecology, University of Illinois; Entomology, Robert L. Metcalf, Ph.D., Professor of Zoology and of Entomology and Head of the De- partment of Zoology, University of Illinois: and Gilbert P. Waldbauer, Ph.D., Professor of Entomology, Uni- versity of Ulinois ; Statistics, Horace W. Norton, Ph.D., Professor of Statistical Design and Analysis, University of Illinois. Ted W. Storck, B.S.. Junior Professional Scientist Richard J. Baur, M.S., Research Ass^istant TiijM Hill, M.S., Research Assistant Richard Kocher, B.S., Research Assistant Robert Moran, M.S., Research Assistant Linda Klippert, B.S., Technical Assistant C. Russell Rose, Field Assistant Section of Faunistic Surveys and Insect Identification Philip W. Smith, Ph.D., Taxonomist and Head Wallace E. LaBerge, Ph.D., Taxonomist Milton W. Sanderson, Ph.D., Taxonomist Lewis J. Stannard, Jr., Ph.D., Taxonomist Larry M. Page, Ph.D.. Assistant Taxonomist John D. Unzicker, Ph.D., Assistant Taxonomist Donald W. Webb, M.S., Assistant Taxonomist Bernice p. Sweeney, Junior Professional Scientist Section of Wildlife Research Glen C. Sanderson, Ph.D., Wildlife Specialist and Head Frank C. Bellrose, B.S., Wildlife Specialist Jean W. Graber, Ph.D., Wildlife Specialist Richard R. Graber, Ph.D., Wildlife Specialist Harold C. Hanson, Ph.D., Wildlife Specialist Ronald F. Labisky, Ph.D., Wildlife Specialist William L. Anderson, M.A,, Associate Wildlife Special- ist W. W. Cochran, Jr., B.S., Associate Wildlife Specialist AViLLiAM R. Edwards, M.S., Associate Wildlife Special- ist Jack A. Ellis, M.S., Associate Wildlife Specialist G. Blair Joselyn, M.S., Associate Wildlife Specialist Charles M. Nixon, M.S., Associate Wildlife Specialist Kenneth E. Smith, Ph.D., Associate Chemist Ronald L. Westemeier, M.S., Associate Wildlife Spe- cialist Stephen P. Havera, M.S.. Assistant Wildlife Specialist David R. Vance, M.S., Assistant Wildlife Specialist Ronald E. Duzan, Junior Professional Scientist Helen C. Schultz, M.A., Junior Professional Scientist Eleanore Wilson. Junior Professional Scientist Sharon Fradenburgh, B.A., Laboratory Technician Robert D. Crompton, Field Assistant James W. Seets, Laboratory Assistant Section of Administrative Services Robert O. Watson, B.S., Administrator and Head nts Supporting Services BiLLMAN, Maintenance Supervisor Dillman. Property Control Trust Ac Robert O. Ellis, Assistant for Operations Lloyd E. Huffman, Stockroom Manager J. William Lusk. Mailing and Distribution Services Melvin E. Schwartz, Financial Records James E. Sergent, Greenhouse Superintendent Publications and Public Relations Owen F. Glissendorf, M.S., Technical Editor Robert M. Zewadski, M.S., Associate Technical Editor Shirley McClellan, Assistant Technical Editor Lloyd LeMere, Technical Illustrator Lawrence S. Farlow, Technical Photographer Technical Library Doris F. Dodds. M.S.L.S., Technical Librarian Doris L. Sublette, M.S.L.S., Assistant Technical Li- CONTENTS Acknowledgments 114 Literature Review 115 Materials and Methods 116 Results 122 Initial Spread of Phloem Necrosis 122 Appearance and Spread of Phloem Necrosis in the 700 Block of South Lynn Street, Champaign, 1949-1951 123 Spread of Phloem Necrosis in 1951 and 1952 and Influence of Phloem Necrosis on the Early Spread of Dutch Elm Disease 123 Appearance of Dutch Elm Disease and Locations of Elms Having Dutch Elm Disease, 1951-1953 124 Spread of Dutch Elm Disease in the 700 Block of West Michigan Avenue, Urbana, 1955-1959 127 Spread of Phloem Necrosis and Dutch Elm Disease on Springfield Avenue, Champaign, 1955-1959 128 Phloem Necrosis-Affected Elms That Later Showed Symptoms of Dutch Elm Disease 130 Incidence of Phloem Necrosis and Dutch Elm Disease in Champaign- Urbana, 1944-1972 130 Phloem Necrosis 132 Dutch Elm Disease 133 Effect of Each Disease on the Residual Population of Elms 134 Accumulated Percentages of Elms Killed bv Each Disease, 1944-1972 .' 134 Time of Year in Which Elms Died from Phloem Necrosis and Dutch Elm Disease 135 Period of Time in Which Elms Died Following the Appearance of Foliage Wilt of Phloem Necrosis or Dutch Elm Disease 136 Discussion 137 Summary 139 ' Literature Cited 141 IIndex 142 This report is printed by authority of the State of Illinois. IRS Ch. 127, Par. 58.12. \lt is a contribution from the Section of Botany and Plant Pathology of the Illinois Natural History Survey. > J. Cedric Carter is Plant Pathologist and Head. Section of Botany and Plant Pathol- 1 ogy. Illinois Natural History Survey. Lucile Rogers Carter. Catalog Department, Univer- t sity Library, University of Illinois, assisted in various aspects of the study reported here. (31556—3M—5-74) Frontispiece.—These before and after pictures along the Broadwalk on the University of lllii i campus illustrate vividly how a cathedral-like archway of stately American elms can be destroyed qui( v and completely by phloem necrosis and Dutch elm disease. The upper photograph was taken in S • tember 1954. The lower photograph was taken in September 1966, several years after the uni\ sity had begun replacing the elms with other species. (Upper photo by W. E. Clark; lower photo i W. D. Zehrl An Urban Epiphytotic of Phloem Necrosis and Dutch Elm Disease, 1944-1972 J. Cedric Carter Lucile Rogers Carter THE AMERICAN ELM was used more extensively than any other species as a shade tree in Ilhnois prior to 1940. It was especially valued for its rapid growth, majestic size, vase shape, and extensive shade. It was used for streets, boulevards, and park drives, as well as in lawns. In many cities throughout the state it represented half or more of the shade trees lining the streets. In some cities it was estimated that three-fourths of the shade trees were American elms. Because of the loss to diseases of millions of elms, espe- cially American elms, since 1940, most cities and homeowners now plant other trees. The elm problem has made many people aware of the importance of using diversified plantings to avoid such a catastrophe in the future. Extensive dying of elms in central Illinois, especially in Bloomington, Nor- mal, and Champaign, occurred as early as 1883 (Forbes 1885:112; 1912:3). This dying of elms subsided within a few years. Although the cause of the elm deaths was not determined, the symptoms reported are not typical of any current vascular wilt disease. In 1907 elms were reported dying in southern Illinois in and around Fairfield in Wayne County. By 1912 numerous elms were dying in 14 towns ( Cairo, Carbondale, Centralia, Clayton, Du Quoin, Edwardsville, Fairfield, Gala- tia, McLeansboro, Mt. Vernon, Quincy, Robinson, Sumner, and VandaUa) in 13 counties in southern and western Illinois (Forbes 1912:5). Careful ex- amination of affected trees revealed that although the small fibrous roots were dead, some of the main roots were alive, as were some of the leaves. This early dying of elms was generally referred to as "elm blight" and at- tributed to various conditions and agen- cies, including drought, exhaustion of soil nutrients, insect attack (borers and bark beetles), and diseases of unknown causes (Forbes 1912:7-10). Following 1912 no reports of ex- tensi\'e dying of elms appeared until 1930, when many elms were killed in and near several large and small cities, notably Hillsboro in south-central Illi- nois, Danville in east-central Illinois, Peoria in north-central Illinois, Quincy in west-central Illinois, and Cairo at the southern tip of the state (Carter 1945:23). By 1940 (Carter 1954) elms were dying throughout the southern half of the state and as far north as Danville on the east and Quincy on the west. Other towns on the northern border of this area in- cluded Charleston, Shelbyville, Taylor- ville, and Pittsfield. The greatest num- ber of affected trees were in a broad belt extending diagonally southwest- ward from Danville and Paris on the east to Alton and Belknille on the west. This area is north of the southern part of the state where heavy losses of elms occurred earlier. This dying of elms continued to spread northward to Ur- bana in 1944, to Mattoon, Springfield, and Lincoln in 1945, and to Decatur, Bloomington, and the area around Bur- lington, Iowa, in 1948. General and widespread dying of elms became stabilized by 1948 with the northern boundary of the affected area repre- sented by a line extending from Dan- ville on the east through Champaign- Urbana, Bloomington, and Peoria to the area around Burlington, Iowa, on the west. North of this area dying elms were found in only six cities— Melvin 113 Ti.i.iNois Nattisal Histohy Survey Bulletin Vol. 31, Art. 4 and Dwight in 1945, Rockford in 1946, Chebanse in 1950, and Chenoa and Onarga in 1953. Following the 1938 report that a dis- ease of a virus nature was killing elms in Ohio (Swingle 1938), it was soon detennined that the widespread dying of elms in the Ohio Valley region of the Midwest was caused by the same disease. It was determined to be a virus disease called phloem necrosis (Swingle 1940 and 1942). However, recent work by Wilson et al. ( 1972 ) indicates that elm phloem necrosis may be caused by a mycoplasmalike or- ganism (MLO). The symptoms exhibited by dying elms in Illinois as early as 1912 were typ- ical of those described later for phloem necrosis. It appears that this disease was the major cause of elms dying in southern lUinois from 1907 to 1950. Dutch elm disease, caused by Cera- tocystis uhni ( Buism. ) C. Moreau, was discovered in one American elm in Coles County (east-central Illinois) in 1950, and the disease spread rapidly, especially in the area where elm phloem necrosis was killing thousands of elms annually. By 1969 it had spread into all 102 counties of the state. At present each disease kills many ehns annually, phloem necrosis in the south- ern two-thirds of the state and Dutch elm disease throughout the state. The first symptom of phloem necrosis is the dying of fibrous roots. This symptom is followed by foliage symp- toms, which appear as drooping leaf blades and upward curling leaf mar- gins. Next the leaves turn yellow, brown, or both, and drop from the tree. These symptoms may occur over one or more growing seasons. On some trees the foliage wilts rapidly within a few weeks and turns brown, but many leaves remain attached to the branches. Occasionally a tree may have one or a few large branches dying simultane- ously over a period of 1 or more years. The infection of individual branches by the Dutch elm disease fungus re- sults in wilting and dying foliage on the aff'ected branches. Frequently, the early symptom of Dutch elm disease is wilting foliage on one or a few branches. Wilt of the entire tree oc- curs after the fungus becomes systemic in the tree. The yellowing of leaves over the entire crown is uncommon in Dutch elm disease but common in phloem necrosis. The present study was initiated, fol- lowing the appearance of phloem necrosis in Urbana in 1944, to obtain data on the number of elms affected annually by the disease and to study the pattern of spread in a municipal area where no city-wide control pro- gram was practiced. With the appear- ance of Dutch elm disease in Urbana in 1951, the study was expanded to include both diseases and the relation- ship of the two diseases in a municipal ACKNOWLEDGMENTS The authors wish to express their sincere appreciation to all those who have assisted or advised in any way during the course of this investigation. Special recognition is given to Drs. Dan Neely, J. L. Forsberg, and J. W. Gerdemann for reviewing and making numerous helpful suggestions in the preparation of the manuscript. The photograph for Fig. 9 was taken by William Clark, formerly Natural History Survey Photographer. All other illustrations, except as noted, were photographed by Wilmer Zehr, Survey Photographer. The illustrations in Fig. 5, 7, 8, 10, 11, and 12 were prepared by Lloyd LeMere, Survey Illustrator. We are grateful to Robert M. Zewad- ski. Survey Associate Editor, for his painstaking efforts in editing the manu- script and to Mrs. Betty Ann Nelson for typing the manuscript. The research policies of the Natural History Survey made it possible for the authors to carry on this study over a period of 29 years. May, 1974 Carter & Carter: Phloem Necrosis and DrrcH Elm Disease LITERATURE REVIEW Field-grown elms do not show symp- toms of phloem necrosis for 1 or more years following the introduction of the MLO (Baker 1949:729, 730; Campana 1958). Elms affected b>' this disease usually die during the growing season in which symptoms first appear. How- ever, some elms may show symptoms for two or sometimes three growing seasons before dying (Campana 1958; Swingle 1938:757). Phloem necrosis affects only the American elm (Ulmus americana L. ) and its cultivars and the winged elm ( U. data Michx. ). The phloem necrosis MLO is carried by the elm leafhopper {Scaphoideus Juteohts Van D. ) . The MLO is introduced into the leaves of healthy elms by the feed- ing activity of elm leafhoppers that have previously fed on leaves of phloem necrosis-affected elms. Elms affected by Dutch elm disease may die during the growing season when symptoms first appear, or they may die during the following growing season. Occasionally an affected elm may not die until the third growing season (Banfield, Rex, & May 1947). Dutch elm disease affects all elm spe- cies, but the Asiatic species are rela- tively resistant (Bretz, Swingle, & Parker 1945). The American elm ap- pears to be more susceptible than the other native and European species (Neely & Carter 1965). Published data on the loss of elms in municipal areas where both diseases occur are limited. However, data are available on losses caused by each disease in areas where only one was present (Campana & Carter 1955 and 1957; Carter 1954, 19.55, and 1961; Neely, Carter, & Campana I960; Neelv 1967). In municipal plantings of elms, losses resulting from phloem necrosis may increase from a few scattered trees when the disease is first discovered to several hundred trees annually within 3 years. In three municipalities in central Illinois the number of phloem necrosis-affected elms increased from 9 in 1945 to .370 in 1948 in Lincoln, from 5 in 1945 to 417 in 1948 in Mattoon (Carter 1950:50), and from 6 in 1948 to 154 in 1951 in Bloomington.' In Mt. Pulaski, which had approxi- mately 600 elms in 1942 when phloem necrosis was first found there, all but 19 elms were killed by the disease by 1948 (J. C. Carter, unpubhshed data). Phloem necrosis also kills elms in rural areas. In a survey made in south- ern Illinois in 1945, the numbers of elms recorded as dying from phloem necrosis were 1,644 in rural areas and 1,655 in municipal areas (Carter 1954). In municipal plantings of elms, Dutch elm disease losses may increase from a few scattered trees when the disease is first discovered to hundreds of trees each year in a few years. In five munici- palities in northern Illinois where Dutch elm disease was discovered in 1955 and where phloem necrosis was not present, the total numbers of diseased elms from 1955 through 1961 were over 4,400 in Aurora, 1,600 in Elgin, 2,500 in Joliet, 1,400 in Waukegan, and 1,000 in Zion. The percentages of the original elm populations that became diseased in these five cities during this period were 48, 23, 33, 11, and 27, respectively (Neely 1967: 513). In Bloomington in north-central Illinois, Dutch elm dis- ease was first found affecting 10 elms in 1954 following a 6-year period in which 9.32 elms were affected by phloem necrosis. The number of elms affected annually by Dutch elm dis- ease increased to 242 in 1955 and to 507 in 1956 (Campana & Carter 1957: 636). In areas where both diseases are present, the incidence of phloem ne- crosis results in an increase in the oc- currence of Dutch elm disease (Cam- pana & Carter 1955). The native elm bark beetle (Hyhirgopinus rufipes Eichh. ) and the smaller European elm 1 The data on the loss of elms in Bloomington were obtained by annual surveys made by the senior author. Illinois Natckal History Survey Bulletin Vol. 31, Art. 4 bark beetle (Scoh/tiis miiUistriotus Marsh.), vectors of the Dutch ehn disease fungus, colonize and overwinter in the bark of weakened, dying, and recently killed elms, including those affected by phloem necrosis. The incidence of Dutch elm disease does not increase the occurrence of phloem necrosis (Campana 1958). Elms killed by either disease and left stand- ing are not colonized by the elm leaf- hopper (S. luteoliis Van D. ), vector of the phloem necrosis MLO. This insect overwinters in the egg stage. The eggs are embedded in the soft cork parenchyma of elm bark (Baker 1949: 731). Dutch elm disease may not only ob- scure the presence of phloem necrosis, but it may kill phloem necrosis-af- fected trees before external symptoms of phloem necrosis become apparent (Campana & Carter 1957; Campana 1958). The rate of increase of Dutch elm disease exceeds that of phloem necrosis in areas where Dutch elm disease appears after phloem necrosis has been present for several years (Campana & Carter 1957:639; Carter 1955:36-37; Neely, Carter, & Campana 1960:167, 169). Phloem necrosis-affected elms colo- nized by smaller European elm bark beetles infested with the Dutch elm disease fungus will harbor that fungus. Of 40 such trees examined in Urbana in 1952, 8 contained the Dutch elm disease fungus (Campana 1954:358).^ Populations of the smaller European elm bark beetle increase rapidly in areas where dying and recently killed elms are present. This situation was common in the 1950's in the southern two-thirds of Illinois where thousands of elms killed annually by phloem ne- crosis were not removed immediately upon discovery of the disease (Cam- pana 1954). 2 Data originally gathered by E, B. Himelick, Illinois Natural History Survey, and published by Campana. When symptoms of both diseases occur in one elm, infection by the phloem necrosis MLO most likely oc- curs first, since the MLO is in the tree 1 year or more before symptoms of phloem necrosis become apparent' (Baker 1948 and 1949:729, 730; Cam- pana 1958; Swingle 1938). Therefore, elms showing early symptoms of phloem necrosis may show symptoms of Dutch elm disease later in the same year or in the following year before they die. Elms infected by the phloem necrosis MLO and the Dutch elm disease fungus in the same year may show symptoms of Dutch elm disease in that year, but not symptoms of phloem necrosis. Some of the data presented in this bulletin on the loss of elms from phloem necrosis and Dutch elm disease in Champaign and Urbana have been re- ported previously (Campana & Carter 1955 and 1957; Carter 1955; Neely, Carter, & Campana 1960). MATERIALS AND METHODS The twin cities of Champaign and Urbana represent a contiguous munici- pal area with a common boundary. This area is approximately 5 miles [8 km] east and west and 2.5 miles [4 km] north and south. It is traversed by approximately 200 miles [320 km] of streets, mostly lined with trees on each side and with additional trees in lawms. In 1950 all elms and all other species' of trees were counted in 75 city blocks' to obtain an estimate of the entire tree population as well as the elm popula- tion. To obtain the estimate, the entire tree population was divided into 25 areas. The areas were selected so that each area included elms of a given size and age. The sizes of trees counted varied from approximately 4 to 20 inches [100-500 mm] in trunk diameter and 20-75 feet [6-23 m] in height. Most of the larger elms were present in the older residential areas. All trees were counted in each of three blocks selected at random in each May, 1974 Carter & Cartel!: Phloem Necrosis and Dltch Elm Disease of the 25 areas. From the data ob- tained (Table 1) it was estimated that there were 12,195 elms in the munici- pal study area. The data also showed that the tree population was composed of 51 percent elms and 49 percent other species. An estimated 2,000 elms in Crystal Lake Park in the north part of Urbana were later included in the total elm population, bringing to 14,195 the estimated number of elms in the Table 1 .—Estimated tree population in Champaign-Urbana, Illinois, in 1950. Elms Other Species City Tm.inois Natural History Survey Bulletin Vol. 31, Art. 4 English elms. Asiatic species were not included, as they are immune to phloem necrosis and resistant to Dutch elm disease. The elms on the University of Illinois campus were sprayed for 5 years to control phloem necrosis, and therefore they were not included in this study. Elms removed from the study area but not affected by phloem necrosis or Fig. 2.—Dutch elm disease symptoms. Dutch elm disease frequently appears as wilt- ing and browning of foliage on one or a few branches. This tree has foliage wilting on the left major branch. (Photo by J. C. Carter) May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease Illinois Natural History Survey Bulletin Vol. 31, Art. 4 Dutch elm disease, except seven elms removed in 1967 because of ice damage, were not included in the total number of trees recorded in this study. How- ever, elms that became large enough to be seen from the street during the 29-year period were included. The appearance and spread of each disease were recorded, starting wdth the first two trees attacked by phloem necrosis in 1944. Dutch elm disease did not appear until 1951. Observations were made at irregular intervals during the growing season from 1944 through 1950 to determine the incidence and pattern of spread of phloem necrosis. Diseased trees were located by frequent scoutings. As many as 8-14 scoutings were made in a grow- ing season. After 1950, the authors made two surveys annually through 1972, one in June and one in September. However, in some years the first survey was not Fig. 4.—Distribution of 16 Champaign-Urbana, Illinois, elms affected by phloem necrosis from 1944 through 1948 (dated according to year when symptoms appeared) and of 412 May, 1974 Carter & Carter; Phloem Necrosis and Dutch Elm Disease completed until early July and the sec- ond survey was not completed until early October. Each survey was made by observing all elms visible from the street while traveling by automobile. This type of survey necessitated driving 200 miles [320 km] of streets, which required a maximum driving time of 24 hours. We used our personal auto- mobile, and the surveying was done in the evenings and on Saturdays. The presence of phloem necrosis dur- ing the years of low initial incidence, 1944-1948, was determined by examin- ing the inner phloem for the butter- scotch color and wintergreen odor char- acteristic of the disease. Dutch elm disease during the years of low initial incidence, 1951-1952, was identified by a laboratory culture test for the fungus. Following the years of low initial incidence, each disease was recognized by foUage symptoms. Phloem necrosis- elms affected by phloem necrosis in 1949 and 1950 (black dots). Some dots represent more than one tree where the elms were less than 30 feet [9 m] apart. Illinois Natural History Survey Bulletin Vol. 31, Art. 4 afFected trees commonly show yellow- ing and wilting of leaves over the en- tire crown (Fig. 1), while Dutch elm disease-affected trees frequently have wilted foliage only on one or a few branches (Fig. 2). However, some Dutch elm disease-affected trees show general wilting on the entire crown. Leaves on such trees usually display less yellowing but more rapid browning and wilting than leaves show on phloem necrosis-affected trees. When there was doubt as to which disease was involved, a diagnosis was usually made by exam- ining wood and bark samples. Also, the accuracy of diagnosis by observation from an automobile was tested by ex- amining an occasional elm for wood and bark symptoms. Data were recorded as to which dis- ease was involved and whether a tree was wilting or dead. The stage or amount of wilt evident at the time of each survey was indicated by listing each tree showing the early, intermedi- ate, or late stage of wilt. All dead elms were listed as dead, and all trees were listed by street address and whether on public or private property. RESULTS INITIAL SPREAD OF PHLOEM NECROSIS Following the discovery in Urbana of phloem necrosis in two elms in 1944, one elm was affected by this disease in 1945, two in 1946, three in 1947, and eight in 1948 (Fig. 3). The tree affected in 1945 was about 300 feet [90 m] west of the two elms affected in 1944. Of the two elms affected in 1946, one was about 400 feet [120 m] farther west and one was about 1,900 feet [580 m] southeast of the elms affected in 1944 and 1945. Of the three elms affected in 1947, one was about 150 feet [45 m] northeast of a tree affected in 1946. The other two were on a line between trees affected in 1944 and 1946 and over 600 feet [180 m] from the nearest previously diseased elm. One of the eight elms affected in 1948 was about 150 feet [45 m] north of an elm affected in 1947. The remaining seven elms were scattered west of previously affected trees. They ranged from about 700 to 8,000 feet [210-2,440 m] from the nearest previ- ously diseased elms. Although the di- rection of the spread of phloem necrosis was generally west and south, each dis- eased tree was surrounded by numerous healthy elms. The two elms that showed phloem necrosis symptoms in 1944 were in the 200 block of West Main Street in Urbana. They were among the oldest elms in the city. They were surrounded by numerous elms except for the three- square-block area of the business dis- trict of Urbana, starting in the 100 block of West Main Street. East of the business district, elms were abun- dant to the east city limit. Each of the 14 elms that became diseased from 1945 through 1948 represented a sep- arate infection center, as none of them was within root-grafting distance of other affected trees ( Himelick & Neely 1962; Verrall & Graham 1935). Each diseased tree was surrounded by healthy elms. In 1949 and 1950 the number of diseased trees increased rapidly in Urbana. The disease was confined al- most entirely to an area in south-central Urbana approximately 12 blocks square and extending south from the 200 block of West Main Street, the location of the two elms that first contracted phloem necrosis. By 1951, when Dutch elm disease was first found in Urbana, phloem necrosis was concentrated in this 12-block area and scattered at random in all directions around 7 of the 12 previously diseased Urbana elms, as shown in Fig. 4. The disease had not invaded an area six blocks wide along the west boundary of Urbana. In Champaign the disease appeared in the 700 block of South Lynn Street in 1949. By 1951 it had spread to many surrounding elms, as described subsequently. A few scattered elms north of this area and two elms within I May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease two blocks of the west boundary of Champaign were also diseased. No elms were affected within the immedi- ate areas surrounding the four Cham- paign elms that became diseased be- fore 1949. APPEARANCE AND SPREAD OF PHLOEM NECROSIS IN THE 700 BLOCK OF SOUTH LYNN STREET, CHAMPAIGN, 1949-1951 Only four elms showed symptoms of phloem necrosis in the entire city of Champaign in 1948, the year before the disease appeared in the 700 block of South Lynn Street. The nearest of these four elms was over 1,200 feet [370 m] northeast of the South Lynn Street 700 block (Fig. 4). Of the 36 elms in that block, 23 were on the west side of the street and 13 were on the east side. On the west side 21 were parkway trees and 2 were on private property, while 8 were park- way trees and 5 were on private prop- erty on the east side of the street. Each of the 21 parkway elms and 2 private- property elms on the west side of the street were within root-grafting dis- tance of one or more elms (Fig. 5). The number of elms having phloem necrosis each year and the month in which symptoms were first observed are shown in Fig. 5. On South Lynn Street, 8 elms wilted in 1949, 21 in 1950, and 7 in 1951. Of the eight elms that wilted in 1949, seven were on the west side of the street, and each was separated from the others by at least one elm that did not show wilt symptoms in 1949. Of 11 closely planted parkway elms on the west side of the street, every other one (5 trees) wilted in 1949, and the remaining 6 trees wilted in 1950. The wilting of eight elms in 1949 suggests that the elm leafhopper, vector of the phloem necrosis MLO, fed ex- tensively on the trees in this limited area before 1949. Since all 36 elms wilted within 3 years, all transmission of the MLO may have been by the elm leafhopper. However, most of the JOHN ST. 6-50 701 6-51 ' 703 9-49 6-50^ 705 9-49 6-50 707 9-49- 6-50- 709 r 9-49 6-50_ZIL 9-49 6-51^^13. 6-50 ^ 715 6-5.0 717 ^ 9-49 719 I 6-50 721 723 6-49. 725 124 Illinois Natttral History Survey Bttlletin Vol. 31, Art. 4 Table 2.—Spread of phloem necrosis in Champaign-Urbana, Illinois, in 1951 and 1952 in relation to the location of elms affected by phloem necrosis in the previous year. Diseased Elms Elms Within Root-Grafting Distance of Previously Diseased Trees Number Percent Elms Beyond Root-Grafting Distance of Previously Diseased Trees 1951 May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease 125 Eleven elms were killed by Dutch area in 1952. Of these 11 elms, 3 elm disease in the Champaign-Urbana were adjacent to elms that were wilting c E o ?5 126 Illinois Natural History Survey Bttlletin Vol. 31, Art. 4 from or had been killed by phloem necrosis. Of these three, one was ad- jacent to a phloem necrosis-affected elm that wilted in 1950 and 1951 and was dead by 1952. One was adjacent to an elm that wilted in 1950, and one was adjacent to two elms. One of these two elms wilted in 1950, and the other wilted in 1951. The remaining eight elms affected by Dutch elm disease in 1952 were isolated trees that were not adjacent to phloem necrosis-affected elms or to the one elm affected by Dutch elm disease in 1951. The locations of 164 elms affected by Dutch elm disease in 1953 and their relation to phloem necrosis-affected elms are shown in Fig. 6 (some loca- tions represent more than one tree). Twenty-seven locations of Dutch elm disease-affected elms were in areas where phloem necrosis was abundant, as indicated by the three areas enclosed by heavy lines in Fig. 6. Ten other locations were immediately adjacent to one or more phloem necrosis-affected elms. The locations of the remaining 41 Dutch elm disease-affected trees No cross street between the 600 and 700 block 9-2-59 702 704 9-21-56 7-2-57 9-14-57 7-2-57 6-14-58 10-1-58 \ 712 9-2l;55V-^-^ May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease were not adjacent to phloem necrosis- affected elms but were widely scattered throughout much of the Champaign- Urbana area. Only one of the 176 elms affected by Dutch elm disease during this 3-year period, 1951-1953, was within root- grafting distance of an elm previously affected by Dutch elm disease. This one elm wilted in 1953 and was ad- jacent to an elm that wilted in 1952. Therefore, the Dutch elm disease fun- gus was carried to the remaining 175 elms by elm bark beetles. SPREAD OF DUTCH ELM DISEASE IN THE 700 BLOCK OF WEST MICHIGAN AVENUE, URBANA, 1955-1959 Elms began dying in the 700 block of West Michigan Avenue, Urbana, in 1955, when four elms wilted, three from Dutch elm disease and one from phloem necrosis. Elms affected by Dutch elm disease before 1955 within one block of this area were: one in 1951, two in 1953, and three in 1954. Phloem necrosis did not occur within one block of this area before 1955. There were 29 American elms (23 in the parkway and 6 on private prop- erty) in this area in June 1955 when the first 3 showed wilt symptoms of Dutch elm disease. The location of each tree is indicated in Fig. 7. The date is shown when wilt symptoms were first observed on each tree. The annual loss of elms is given in Table 4. Of the 28 elms killed in this block by Dutch elm disease in 5 years, more ( 10 trees ) were killed in the third year than in any other year of the study. No elm within root-grafting distance of previously diseased trees showed wilt symptoms in the second year. Thirteen (46 percent) of the trees were within root-grafting distance of previously dis- eased trees. Therefore, they may have become infected through roots grafted to those of previously diseased elms. The remaining 15 elms (54 percent), not within root-grafting distance of pre- viously diseased trees, became infected 2 £ Q s 5 c5 Oh .Q ^ 5 Q SO o o CC CO O 00 -^ S S S W r^; h IixiNois Natural History Sttrvet Bxjixetin Vol. 31, Art. 4 through insect transmission of the fun- gus. SPREAD OF PHLOEM NECROSIS AND DUTCH ELM DISEASE ON SPRINGFIELD AVENUE, CHAMPAIGN, 1955-1959 Elms in a six-block section of East Springfield Avenue, Champaign, be- tween First and Wright Streets, began dying in 1955 when one elm wilted from Dutch elm disease. Phloem necrosis did not appear in this area until 1957, when one elm contracted that disease. Sev- eral elms within three blocks of Spring- field Avenue were attacked by each of these diseases before 1955. Two elms died from phloem necrosis in 1953, one located two blocks northwest of the DED— 9-6-58- DED—9-6-58— ^ ZhDED — 6-14-58- DEO— 9-6-58-p* DED—6-28-55-^ PN 6-I4-58-. ^9-6-58-^ I DED f-9-14-57-' ^9-6-58 — 7 WRIGHT ST. 1st ST. -DED—9-6-58 -PN 6-|4-5B~ -DED—9-6-58 '-PN—6-14-58 -DED—9-14-57 S-=DED—9-6-58 — >-6-|4-58 •IFded-) /t ;— utu— \ 6-14-58 9-14-57 Fig, 8.—The spread of phloem necrosis (PN) and Dutch elm disease (DED) on East Springfield Avenue, Champaign, Illinois, 1955-1959. a -; Q is '^ .2 CQ Tt< iH t* C» SI tH Csl U5 00 iH ^ a> CD c> cq -^ oi t^ oq W .2 rH N ^ eq i-l 2 t- 03 03 o> t tH tH r-t iH rH en :May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease 100 block and one located two and one- half blocks south of the 600 block of East Springfield Avenue. Twelve elms died from Dutch elm disease, two in 1953 and ten in 1954. One of the two elms that died in 1953 was two blocks west and one was one block north of the 100 block of East Springfield Ave- nue. Of the 10 elms that died in 1954, 7 were one block distant from the 100 and 200 blocks, and 3 were tsvo blocks from the 400 block of East Springfield Avenue. The parkway along this six-block stretch was lined with 40 Moline elms in 1950. Each tree was approximately 1 foot [0.3 m] in trunk diameter. Seven larger American elms along the same section were located on private prop- erty. The locations of these 47 elms are indicated in Fig. 8. The 25 elms that wilted in 1955 on streets that cross East Springfield Avenue were beyond root-grafting distance of the elms along Springfield Avenue. All 47 elms on East Springfield Avenue became af- fected by phloem necrosis or Dutch elm disease and died within 5 vears, 1955-1959. Of the 47 elms killed in 5 years along East Springfield Avenue, Champaign, 17 (36 percent) were killed in 2 years by phloem necrosis, while 30 (64 per- cent) were killed in 5 years by Dutch elm disease. The disease involved and the year that each tree became diseased are shown in Table 5. A rapid increase in the number of trees affected by each disease occurred in the year following the appearance of phloem necrosis and in the third year following the appearance of Dutch elm disease. Two of the trees killed by phloem necrosis on the south side of the 100 block of East Springfield Axenue in 1958 were within root-graft- ing distance of a tree killed by phloem necrosis in 1957 (Fig. 9). Six of the trees on East Springfield Avenue killed by Dutch ehn disease between 1955 and Fig. 9.—Moline elms on the south side of the 100 block of East Springfield Avenue, Champaign, Illinois. The first four elms on the right were killed by phloem necrosis. The fifth elm and one elm east of this fifth tree, removed before the picture was taken, were killed by Dutch elm disease. The second elm from the right died in 1957, and the others died in 1 958. (Photo by W. E, Clark) Illinois Natural History StmvET BtrtLETiN Vol. 31, Art. 4 tember following the appearance of phloem necrosis symptoms in the pre- vious June, 123 (80.4 percent) in the year following the appearance of phloem necrosis symptoms, and only two (1.3 percent) in the second year following the appearance of phloem necrosis symptoms. In general, the percentage of phloem necrosis-affected elms that subsequently showed Dutch elm disease increased as the number of elms affected by Dutch elm disease increased. Many elms that become infected with the Dutch elm disease fungus in June wilt during the same growing season. Therefore, it is not surprising that 28 elms that showed phloem necrosis symptoms in June showed Dutch elm disease symptoms by the following September. Elms which had been wilting from phloem necrosis in June and were wilting from Dutch elm disease in September most likely became infected by the Dutch elm disease fungus in June, when phloem necrosis symptoms were already evident. INCIDENCE OF PHLOEM NECROSIS AND DUTCH ELM DISEASE IN CHAMPAIGN-URBANA, 1944-1972 To determine the incidence of phloem necrosis and Dutch elm disease in Champaign-Urbana, the number of elms affected annually by each disease Table 6.—Phloem necrosis-affected elms In Champalgn-Urbana, Illinois, that subse- quently contracted Dutch elm disease, 1954-1960. 1959 were within root-grafting distance of trees killed by Dutch elm disease in the previous 1 or 2 years. Three of these six elms were on the north side of the 200 block, one on the north side of the 100 block, one on the south side of the 300 block, and one on the south side of the 500 block. Since 39 of the 47 elms in this area were not within root-grafting distance of previously diseased trees, the spread of each disease occurred mainly by insect transmission of each causal agent. PHLOEM NECROSIS-AFFECTED ELMS THAT LATER SHOWED SYMPTOMS OF DUTCH ELM DISEASE Some elms affected by phloem ne- crosis subsequently became affected by Dutch elm disease before dying. The number of elms that showed phloem necrosis symptoms followed by Dutch elm disease symptoms from 1954 to 1960 is listed in Table 6. During this 7-year period 1,234 trees were affected by phloem necrosis and 10,714 trees were affected by Dutch elm disease. The data are arranged according to the time between the first appearance of phloem necrosis symptoms and the subsequent appearance of Dutch elm disease symptoms. Of the 153 elms affected by both diseases, 28 (18.3 percent) were af- fected by Dutch elm disease in Sep- May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease o S Stf Q CLi ^ Dh C .S rt S .- 9 CD O P < Illinois Natural History Survey Bulletin Vol. 31, Art. 4 was recorded from 1944, when phloem necrosis first appeared, through 1972. The number of ehns affected annually and the percentages of the original and residual elm populations lost each year are recorded in Table 7. The percentages of the original elm popula- tion lost annually to each disease are illustrated in Fig. 10. The percentages of the residual elm population lost an- nually to each disease are illustrated in Fig. 11. Phloem Necrosis A rapid increase in the number of elms affected by phloem necrosis did not occur until 1949, 5 years after the disease had first appeared in two Ur- bana elms. The number of elms af- fected by phloem necrosis in Cham- paign-Urbana increased annually until 1952, when 555 were affected. Follow- ing 1952 the number of phloem ne- crosis-diseased trees decreased annually until 1956, when only 60 elms were killed. This decrease was followed by an increase to 368 affected trees in 1957. After 1957 the number of phloem necrosis-diseased trees decreased rap- idly until 1960, when only 12 elms were affected. From 1961 through 1972 only one to five elms were affected by phloem necrosis annually except in 1969, when no phloem necrosis oc- curred. From 1944 through 1972, a period of 29 years, 2,994 elms were killed by phloem necrosis. The two peak periods of elm deaths from phloem necrosis occurred in 1952 and 1957 (Fig. 10). The cause for the high death rate of elms in 1952 and the subsequent decrease in the inci- dence of phloem necrosis through 1956 was not determined. However, four conditions that may have been involved were ( 1 ) the rapid increase in the incidence of Dutch elm disease, (2) the reduction in the elm population, (3) the time required for symptoms of phloem necrosis to appear following infection, and (4) drought conditions from 1952 through 1955. The incidence of Dutch elm disease increased from 11 trees in 1952 to 1,805 trees in 1955. During this period Dutch elm disease reduced the elm population by 2,674 trees, or 20 percent of the elm population of 1952. The time required for wilt symptoms to appear following infection is longer 16- May, 1974 CuiTjaj & Cartek: Phloem Necrosis and Dutch Elm Disease for phloem necrosis than for Dutch elm disease. Phloem necrosis-affected elms do not show foliage symptoms for at least 1 >'ear following infection, while many Dutch elm disease-affected elms show foliage symptoms in the year when infection occurs. Drought conditions that prevailed from 1952 through 1955, especially in 1953 and 1954, may ha\e caused a re- duction in the elm leafhopper popula- tion, since this insect is adversely af- fected by such conditions. Precipitation for the 5-month growing season. May through September, was 7.89 inches [200.41 mm] below normal in 1953 and 4.19 inches [106.41 mm] below normal in 1954. Total precipitation was 10. .34 inches [262.64 mm] below normal in 1953 and 6.73 inches [170.94 mm] be- low normal in 1954 (Carter 1955:40). Collection records of the Section of Faunistic Sur\eys and Insect Identifica- tion, Illinois Natural History Survey, show that the populations of leafhop- pers in general were drastically reduced during these drought years and that the elm leafhopper has never been col- lected in abundance in Illinois. The increase in the incidence of phloem necrosis from 1957 through 1959 may have been influenced mainly by an increase in the elm leafhopper population, which might be expected in years of near-normal rainfall. Following 1959 the incidence of phloem necrosis decreased to very low levels during the period of rapid decline in the residual elm population. Only 7 per- cent of the original elm population remained by 1960. Dutch Elm Disease A rapid increase in the number of elms affected by Dutch elm disease started in 1953, 2 years after the disease first appeared in Urbana in a single elm. The number of elms affected an- nually by Dutch elm disease increased until 1957, when 2,116 trees were af- fected. During the 5-year period 1955- 1959, the annual loss of elms to Dutch elm disease was 1,770-2,116, with a total loss of 9,331 trees. This number was 82.4 percent of the residual elm population of 11,324 trees in the spring of 1955, or 66.2 percent of the original elm population of 14,103 trees in 1944. The peak incidence of Dutch elm disease (Fig. 10) occurred in 1957, 6 1911 1946 1956 1958 1960 1962 YEAR 1966 1968 1970 1972 Fig. 1 1.—Annual percentages of the residual population of elms lost to phloem necrosis and Dutch eim disease in Champaign-Urbana, Illinois, 1944-1972. 134 Illinois Natural History Subvey Bulletin Vol. 31, Art. 4 years after the disease first appeared in the area. The number of elms killed in 1957 was 2,116, or 15 percent of the original elm population and 28.21 per- cent of the residual elm population. Following 1959 the residual elm popula- tion decreased rapidly until 1963, when only 95 healthy elms remained and only 9 were killed by Dutch elm dis- ease. With the rapid decline in the elm population, the incidence of Dutch elm disease also dechned drastically. From 1964 to 1969 only one to four trees (none in 1967) became affected by this disease annually. No elms were affected in 1970 and 1971, but five elms were affected in 1972. Figure 10 shows that the incidence of Dutch elm disease increased more rapidly, reached a much higher peak, and decreased more rapidly than did the incidence of phloem necrosis. Addi- tionally, only one peak period of elm deaths from Dutch elm disease oc- curred, while there were two peak periods of elm deaths from phloem necrosis. Effect of Each Disease on the Residual Population of Elms The annual loss of elms from each disease in relation to the residual elm population is illustrated in Fig. 11. The annual loss from phloem necrosis fluctu- ated from year to year, reaching five peaks of 5 percent or more of the residual elm population. The highest peak (9.43 percent) occurred in 1971, when the residual elm population was only 53 trees. The next highest peak occurred in 1958, when the residual elm population was 5,016 trees. Following the appearance of Dutch elm disease in 1951, the percentage of the residual elm population killed an- nually by this disease increased rapidly until 1960. In 1960 Dutch elm disease killed 689 trees (72.53 percent) of the residual elm population of 950 trees. Following 1960 the annual loss of trees in the residual elm population de- creased rapidly until 1964 when only 1 elm (1.22 percent) of the residual population of 82 was killed by Dutch elm disease. Accumulated Percentages of Elms Killed by Each Disease, 1944-1972 The accumulated percentages of elms killed by each disease are given in Table 8 and illustrated in Fig. 12. The loss of elms from each disease follows a sigmoid curve. Less than 10 percent of the elm population was killed by both diseases from 1944 through 1952, a period of 9 years. Phloem necrosis was present throughout the 9-year pe- riod, but Dutch elm disease was present for only 2 years. During the second 9-year period, 1953-1961, both diseases killed more than 89 percent of the Table 8.—Accumulated percentages of elms killed by phloem necrosis and Dutch elm dis- ease in Champaign-Urbana, Illinois, from 1944 through 1972. May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease 100 90H 80 70 ^ 60. z u 50- " 40- 30- 20- 10- OH • Phloem necrosis and Dutch elm disease Dutch elm disease — Phloem necrosis 1948 1956 1960 YEARS 1964 1968 Fig. 12.—Accumulated percentages of the original population of 14,103 elms lost each year to phloem necrosis and Dutch elm disease in Champaign-Urbana, Illinois, 1944-1972. original elm population. With less than 1 percent of the elms remaining after IS years, the annual loss became a few trees. Phloem necrosis killed 2,994 elms during the 29-year period, 1944-1972, while Dutch elm disease killed 11,062 elms during the 22-year period, 1951- 1972. Although no elms showed symp- toms of Dutch elm disease in 1970 or 1971, five trees were killed by the dis- ease in 1972. Of the original popula- tion of 14,103 elms in 1944, all but 40 had been killed by the fall of 1972, a period of 29 years. TIME OF YEAR IN WHICH ELMS DIED FROM PHLOEM NECROSIS AND DUTCH ELM DISEASE Starting in 1951 two surveys were made annually to record the number of elms affected by phloem necrosis and by Dutch elm disease. The first survey was made in the early part of the growing season, usually in June. The second survey was made in the late part of the growing season, usually in September. These surveys are referred to as the June and September surveys. Each year data were obtained on the Table 9.—Elms showing disease symptoms in June and September surveys, Champaign- Urbana, Illinois, 1955-1961. 136 Illinois Natural History Survey Bulletin Vol. 31, Art. 4 number of elms affected by each disease in each of the two survey periods. No affected ehn was included in the data of more than one survey. The num- bers of elms affected by each disease at the time of each June and September survey from 1955 through 1961 are recorded in Table 9. Of the 1,056 elms affected by phloem necrosis during this 7-year period, 386 (36.6 percent) showed symptoms in June, and 670 (63.4 percent) showed symptoms in September. Of the 10,139 elms affected by Dutch elm disease, 6,133 (60.5 percent) showed symptoms in June, and 4,006 (39.5 percent) showed symptoms in September. Of the 6,974 dead elms standing at the time of the June and the September surveys during the years 1955-1960, 2,620 (37.6 percent) were standing in June and 4,354 (62.4 percent) were standing in September. PERIOD OF TIME IN WHICH ELMS DIED FOLLOWING THE APPEARANCE OF FOLIAGE WILT OF PHLOEM NECROSIS OR DUTCH ELM DISEASE Not all elms affected by phloem ne- crosis or Dutch elm disease die in the same growing season in which foliage wilt first appears. Some elms wilt dur- ing two, and occasionally three, grow- ing seasons before they die; some elms that have shown no foliage wilt die during the winter. Data on 231 elms affected by phloem necrosis, 3,908 elms affected by Dutch elm disease, and 820 elms that died but showed no foliage wilt are given in Table 10. The data cover the growing seasons of 1955 through 1960. During this period most diseased elms were not removed until after they were dead. This practice made it possible to record the period of time in which the diseased trees died. Of the 231 phloem necrosis-affected elms, 143 (61.9 percent) died in the year following the appearance of wilt. Only 87 ( 37.7 percent ) died in the year that wilt appeared, and only 1 (0.4 percent ) lived until the second year fol- ^•5 ca g o bo ^ ^ i ^ o a CO H May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease lowing the appearance of wilt. Nearly half ( 45.9 percent ) of the elms affected by phloem necrosis continued to live during the remainder of the summer in which wilt symptoms appeared but were dead by June of the next summer. Of the 3,908 Dutch ehn disease- affected elms, 3,134 ( 80.2 percent ) died in the year when wilt symptoms ap- peared. Only 753 (19.3 percent) died during the second year, and 21 (0.5 percent ) died during the third summer. These data indicate that, following the initial appearance of foliage wilt, elms having Dutch elm disease die more rapidly than do elms affected by phloem necrosis. Also of interest are the 820 elms that did not show foliage wilt in the September survey but died before the June survey of the following year. These elms represent 16.5 percent of the 4,959 elms that died during the 6-year period. Although the cause of death was not determined, probably most, if not all, of these elms were killed by Dutch elm disease, since this disease usually causes elms to die more rapidly than does phloem necrosis. DISCUSSION Phloem necrosis was not known to occur in any areas close to Champaign- Urbana when the disease was discov- ered in two adjacent elms in Urbana in 1944. The nearest area where the dis- ease had occurred was Danville, Illi- nois, 32 miles [51 km] east of Urbana. Beginning in 1935, elm plantings be- tween Urbana and Danville had been observed for disease symptoms fre- quently during the growing season of each year. In the course of this study careful examination of phloem samples from wilting elms showed that the charac- teristic butterscotch color usually was present only in the current phloem. However, samples from some wilting elms had butterscotch color in 1- and sometimes 2-year-old phloem. This condition occurred mainly in elms that showed foliage symptoms during two or more growing seasons. Since the but- terscotch color in the current phloem indicates that the tree has been infected for about 1 year (Baker 1949:7.30), the butterscotch color in 1- and 2-year-old phloem indicates that the MLO is in some elms for 2-3 years before foliage wilt appears. Because phloem necrosis was present in the Champaign-Urbana area 7 years ( 1944-1950 ) before Dutch elm disease appeared there, the initial spread of phloem necrosis was not influenced by Dutch elm disease. In Urbana, phloem necrosis spread slowly for 4 years fol- lowing its appearance in 1944. The few affected trees were widely scattered at distances of approximately 300-2,000 feet [100-600 m] from the two elms first attacked. Each affected tree rep- resented a new center of infection from which the disease continued to spread to nearby elms. This intitial spread resulted from transmission of the MLO by the elm leafhopper. The incidence of phloem necrosis in- creased rapidly in Urbana during 1948 and 1949, and by 1950 over 300 trees were affected. The disease was con- centrated mainly within an area ap- proximately 1,400 feet [400 m] wide and 4,000 feet [1,200 m] long in the central part of the city, an area heavily populated with American elms. By 1950 only a few scattered elms were affected beyond this area, and no af- fected trees were in the 3,600-foot-wide [1,100 m] area adjacent to Champaign. In Champaign phloem necrosis was not found until 1948, when it affected four elms. The trees were approxi- mately 5,000 feet [1,500 m] west of any affected trees in Urbana. Following 1948 the number of elms affected by phloem necrosis increased rapidly in Champaign, and all but a few of the affected trees were concentrated in an area two blocks wide and four blocks long, centering around the 700 block of South Lynn Street. Of the 36 elms in the 700 block of South Lynn Street, 8 wilted in 1949. 138 Iij.iNOis Natural History Survey Bulletin Vol. 31, Art. 4 The infection of these eight elms re- sulted from insect transmission of the MLO in 1948 or earlier. Because 28 of the elms in this block wilted in the 2 years following the initial appearance of the disease, it is possible that the MLO was spread by the elm leaf- hopper. However, all but three of these elms were within root-grafting distance of previously affected trees. Following 1950 phloem necrosis spread rapidly throughout both cities, and the greatest loss of trees from this disease in any 1 year occurred in 1952, 8 years after the disease first appeared. Phloem necrosis was widespread when Dutch elm disease was dis- covered in one elm in southwest Ur- bana in 1951. The infection of this elm resulted from insect transmission of the fungus. However, phloem ne- crosis-affected elms may have harbored the inoculum, because the Dutch elm disease fungus was isolated from 8 of 40 elms that had phloem necrosis in 1952 (Campana 1954:358). There- fore, many of the hundreds of elms killed annually by phloem necrosis but not removed promptly served as col- onizing sites for the smaller European elm bark beetle, vector of the Dutch elm disease fungus. Milhons of these insects were present in the Champaign- Urbana area as potential carriers of the Dutch elm disease fungus at the time the disease first appeared. Following the appearance of Dutch elm disease in 1951, the fungus was transmitted by insects in 1952 and 1953, for only 1 of 175 diseased elms was within root-grafting distance of a previ- ously diseased tree. Although only a few elms were affected in 1952, Dutch elm disease spread rapidly in the next 3 years, and a 5-year peak period of elm deaths started in 1955. Dutch elm disease increased annually more rapidly than did phloem necrosis in the number of elms affected and in the number of infection centers. As the incidence of Dutch elm disease increased, the inci- dence of phloem necrosis decreased, and phloem necrosis failed to spread along some streets. During the peak years of loss from i each disease, Dutch elm disease killed 1 approximately four to five times as i many elms as did phloem necrosis. The : peak of elm deaths from Dutch elm i disease occurred over 5 years, while ; the peak of elm deaths from phloem i necrosis occurred in two periods, the first lasting 4 years and the second 2 ! years. Following these peak periods the numbers of elms affected annually by each disease decreased rapidly, for over i 90 percent of the 1944 elm population i of Champaign-Urbana had been killed 1 by 1960. In some blocks and along some streets all elms were killed within i 3-5 years by one or both diseases. All 1 36 elms in the 700 block of South Lynn ; Street in Champaign were killed by phloem necrosis in 3 years, and 28 of ( 29 elms in the 700 block of West Michi- gan Avenue in Urbana were killed by . Dutch elm disease in 5 years. Where both diseases were present, , Dutch elm disease killed more trees i than did phloem necrosis. Dutch elm i disease tends to kill trees more rapidly .' than does phloem necrosis. Most elms s affected by Dutch elm disease die in i the same year in which foliage wilt I appears, but most elms affected by . phloem necrosis die in the year follow- ing the appearance of foliage wilt. Also, more phloem necrosis-affected elms * show wilt symptoms in September than show them in June, while more Dutch , elm disease-affected trees show wilt i' symptoms in June than show them in i September. Some elms die during the: winter without any visible foliage wilt. While each disease may contribute to these winter deaths, it seems likely that Dutch elm disease is mainly respon- sible. Some elms that first showed symp- toms of phloem necrosis subsequently showed symptoms of Dutch elm dis- ease. As the number of elms killed by Dutch elm disease increased, the num- May, 1974 Cartek & Carter: Phloem Necrosis and Dltch Elm Disease ber of phloem necrosis-affected elms subsequently affected by Dutch elm disease increased. This fact suggests that as the supply of Dutch elm disease inoculum increases, more phloem ne- crosis-affected elms are invaded by the Dutch elm disease fungus. Also, the greater the number of elms infested with bark beetles, the greater the chances for the spread of the Dutch elm disease fungus. Although some elms affected by phloem necrosis in June showed Dutch elm disease symptoms in September, in most cases Dutch elm disease symp- toms did not appear until the year following the appearance of phloem necrosis symptoms. Only phloem ne- crosis-affected elms that die slowly during one or more growing seasons can be subsequently affected by and show symptoms of Dutch elm disease. Phloem necrosis-affected elms that are subsequently affected by Dutch elm disease appear to be killed by Dutch elm disease and not by phloem necrosis (Campana & Carter 1955). The cycle of elm deaths from Dutch elm disease probably was affected only slightly, if at all, by the presence of phloem necrosis. This conclusion is based on the fact that elm deaths from Dutch elm disease built up to a peak more rapidly than did elm deaths from phloem necrosis. During the 5-year period 1955-1959 more than eight times as many elms were killed by Dutch elm disease as were killed by phloem necrosis. However, the cycle of elm deaths from phloem necrosis was greatly shortened by the presence of Dutch elm disease; Dutch elm disease killed 78.4 percent of the elms, while phloem necrosis killed only 21.2 per- cent. SUMMARY In the 29-year study reported here, data were recorded on the spread of and losses caused by elm phloem ne- crosis and Dutch elm disease in a mu- nicipal area which had no community- wide control program for either disease. Phloem necrosis appeared in Urbana in 1944, when two trees were affected. Dutch elm disease did not appear until 1951, when one tree was affected. The initial spread of phloem necrosis was not influenced by Dutch elm disease, since Dutch elm disease was not pres- ent during that period. Each of the 14 elms that contracted phloem necrosis from 1945 through 1948 was scattered at random beyond root-grafting dis- tance of other diseased trees, and each tree represented a separate infection center. Phloem necrosis spread rapidly along some streets, killing all 36 elms in one block within 3 years. The early spread of Dutch elm dis- ease was influenced by phloem necrosis. Phloem necrosis-affected elms can har- bor the Dutch elm disease fungus, and the elms killed by phloem necrosis were heavily colonized by the smaller European elm bark beetle, vector of the Dutch elm disease fungus. Many of the phloem necrosis-affected elms were not removed before the bark beetles emerged. Dutch elm disease spread rapidly to elms in areas where phloem necrosis was abundant, and it also affected scattered elms located well away from phloem necrosis-affected elms. How- ever, of 164 elms having Dutch elm disease in 1953 only 41 were in scat- tered locations away from phloem ne- crosis-affected trees. Dutch elm disease, like phloem ne- crosis, spread rapidly to elms along some streets. Twenty-eight elms were killed by this disease in one block in 5 years. Of 47 elms in six blocks of one street, 17 were killed by phloem ne- crosis in 2 years and 30 were killed by Dutch elm disease in 5 years. However, Dutch elm disease was present for 2 years before phloem necrosis appeared. Phloem necrosis and Dutch elm disease were spread mainly by their respective insect vectors in this area, because 39 of the 47 elms were beyond root- Illinois Natural History Survey Bulletin Vol. 31, Art. 4 grafting distance of previously diseased trees. Some phloem necrosis-affected elms subsequently became infected with the Dutch elm disease fungus and showed typical symptoms of Dutch elm disease before dying. The number of phloem necrosis-affected elms that subsequently became affected by Dutch elm disease increased as the incidence of Dutch elm disease increased. The greatest number of elms affected by phloem necrosis in 1 year was 555 trees in 1952, 8 years after the disease was discovered in this area. The great- est number of elms affected by Dutch elm disease was 2,116 trees in 1957, 6 years after the disease was discovered here. Of the original population of 14,103 elms, 2,994, or 21.23 percent, were killed by phloem necrosis in 29 years. Dutch elm disease killed 11,062, or 78.44 percent, in 22 years. Both dis- eases killed 14,056, or 99.67 percent, of the elms. Dutch elm disease had a greater effect on the residual elm popu- lation, since it killed more than three times as many elms as did phloem necrosis. More elms showed symptoms of phloem necrosis in the September sur- vey than showed such symptoms in the June survey. The reverse was true of elms having Dutch elm disease. Fol- lowing the appearance of wilt symp- toms, elms affected by Dutch elm dis- ease tended to die more rapidly than did elms affected by phloem necrosis. Most elms that had Dutch elm disease died in the growing season in which i foliage wilt appeared, while most elms . that contracted phloem necrosis died ! in the year following the appearance of foliage wilt. LITERATURE CITED Baker, W. L. 1948. Transmission by leaf hoppers of the virus causing phloem necrosis of American elm. Science 108: 307-308. . 1949. Studies on the transmission of the virus causing phloem necrosis of American elm, with notes on the biology of its insect vector. Journal of Economic Entomology 42:729-732. B.\NFiELD, W. M., E. G. Rex, and C. May. 1947. Recurrence of Dutch elm disease in American elms in relation to tree stature. Phytopathology 37:1-2. Bretz, T. W., R. U. Swingle, and D. E. Parker. 1945. Some recent observations on elm phloem necrosis and the Dutch elm disease. National Shade Tree Con- ference Proceedings 21:25-28. Campana, R. J. 1954. The present status of Dutch elm disease in Illinois. Plant Disease Reporter 38:356-358. . 1958. Dutch elm disease and elm phloem necrosis. Midwestern Shade Tree Conference Proceedings 13:17-25. , and J. C. Carter. 1955. Spread of Dutch elm disease in Illinois in 1954. Plant Disease Reporter 39:245-248. , and . 1957. The current sta- trol of Dutch elm disease. Illinois State Chamber of Commerce, Chicago. . 1961. Dutch elm disease up-to-date. tus of Dutch elm disease in Illinois. Plant Disease Reporter 41:636-639. Carter, J. C. 1945. Dying of elms in Illi- nois. Plant Disease Reporter 29:23-26. . 1950. Status of oak wilt and elm phloem necrosis in the Midwest. Arbor- ist's News 15:45-51. . 1954. Elm phloem necrosis — re- sume of the situation. Midwestern Shade Tree Conference Proceedings 9:14-16. . 1955. The Champaign-Urbana-Uni- versity of Illinois situation. Pages 36-42 in Control of Dutch elm disease. Proceed- ings of a statewide conference on the con- Midwestern Shade Tree Conference Pro- ceedings 16:34-39. Forbes, S. A. 1885. Insects injurious to the elm. Pages 112-115 in Fourteenth report of the state entomologist on the noxious and beneficial insects of the state of Illinois. . 1912. What is the matter with the elms in Illinois? Illinois Agricultural Ex- periment Station Bulletin 154. 22 pp. HiMELicK, E. B., and D. Neely. 1962. Root grafting of city-planted American elms. Plant Disease Reporter 46:86-87. Neely, D. 1967. Dutch elm disease in Illi- nois cities. Plant Disease Reporter 51: 511-514. , and J. C. Carter. 1965. Species of elm on the University of Illinois campus resistant to Dutch elm disease. Plant Dis- ease Reporter 49:552. , , and R. J. Campana. 1960. The status of Dutch elm disease in Illi- nois. Plant Disease Reporter 44:163-166. Swingle, R. U. 1938. A phloem necrosis of elm. Phytopathology 28:757-759. . 1940. Phloem necrosis in the Ohio River Valley. Phytopathology 30:23. . 1942. Phloem necrosis: a virus disease of the American elm. U.S. De- partment of Agriculture Circular 640. 8 pp. Verrall, a. F., and T. W. Graham. 1935. The transmission of Ceratostomella ulmi through root grafts. Phytopathology 25: 1039-1040. Wilson, C. L., C. E. Seliskar, and C. R. Krause. 1972. Mycoplasmalike bodies associated with elm phloem necrosis. Phytopathology 62:140-143. 141 INDEX Alton, 113 American elm, 113-115, 117, 127, 129, 137 Asiatic elm species, 115, 118 Aurora, 115 Automobile survey, 121 B Bark beetles, 113 Belleville, 113 Bloomington, 113, 115 Borers, 113 Burlington, Iowa, 113 Cairo, 113 Carbondale, 113 Centralia, 113 Ceratocystis ulmi, 114 Champaign, 113, 116-117, 122-125, 127, 129-130, 132, 137-138 Charleston, 113 Chebanse, 114 Chenoa, 114 Clayton, 113 Coles County, 114 Crystal Lake Park, 117 Danville, 113, 137 Decatur, 113 Du Quoin, 113 Dutch elm disease fungus, 114, 116, 124, 127, 138-140 Dutch elm disease symptoms, 114-118, 130 Dwight, 114 Leafhopper, 115, 133 Lincoln, 113 M Mattoon, 113, 115 McLeansboro, 113 Melvin, 113 Midwest, 114 MLO, 114-116, 123, 137-138 Moline elm, 117, 129 Mt. Pulaski, 115 Mt. Vernon, 113 Mycoplasmalike organism (MLO), 114 N Normal, 113 North-central Illinois, 113, 115 Ohio, 114 Ohio Valley, 114 Onarga, 114 Paris, 113 Peoria, 113 Phloem necrosis symptoms, 114, 117, 122, 130 Pittsfield, 113 Quincy, 113 Robinson, 113 Rockford, 114 East-central Illinois, 113-114 East Springfield Avenue, 128-129 Edwardsville, 113 Elgin, 115 "Elm blight," 113 Elm leafhopper, 116, 123, 137 English elm, 117 European elm species, 115, 117 Fairfield, 113 Faunistic Surveys and Insect Identification Section, 133 First Street, 128 Galatia, 113 G H Hillsboro, 113 Himelick, E. B., 124 Hylurgopinus rufipes, 115 J Joliet, 115 June survey, 120, 135-137, 140 Scaphoideus luteolus, 115-116 Scolytus multistriatus, 116 September survey, 120, 135-137, 140 Shelbyville, 113 Slippery elm, 117 Smaller European elm bark beetle, 116, 124, 138-139 South-central Illinois, 113 South Lynn Street, 122-123, 137-138 Springfield, 113 Sumner, 113 Surveys, 120-121 Taylorville, 113 u Ulmus alata, 115 Ulmus americana, 115 University of Illinois campus, 118 Urbana, 113-114, 116-117, 122-125, 127, 130, 132-133, 137-139 V Vandalia, 113 Vector, 116, 123, 138-139 May, 1974 Carteu & Carter: Phloem Necrosis and Dutch Elm Disease Virus, 114 West Michigan Avenue, 127, 138 * West Pennsylvania Avenue, 124W Winged elm, 115 Waukegan, 115 Wright Street, 128 Wayne County, 113 West-central Illinois, 113 Z West Main Street, 122 Zion, 115 Some Publications of the ILLINOIS NATURAL HISTORY SURVEY BULLETIN Volume 30, Article 6.—Comparative Uptake and Biodegradability of DDT and Meth- oxychlor by Aquatic Organisms. By Ke- turah A. Reinbold, Inder P. Kapoor, Wil- liam F. Childers, Willis N. Bruce, and Robert L. Metcalf. June, 1971. 12 p., in- dex. Volume 30, Article 7.—A Comparative Study of Two Components of the Poinsettia Root Rot Complex. By Robert S. Perry. Au- gust, 1971. 35 p., index. Volume 30, Article 8.—Dynamics of Condi- tion Parameters and Organ Measurements in Pheasants. By William L. Anderson. July, 1972. 44 p., index. Volume 31, Article 1.—The Effects of Sup- plemental Feeding and Fall Drawdowns on the Largemouth Bass and Bluegills at Ridge Lake, Illinois. By George W. Ben- nett, H. Wickliffe Adkins, and William F. Childers. January, 1973. 28 p., index. Volume 31, Article 2.—The Reproductive Cycle of the Raccoon in Illinois. By Glen C. Sanderson and A. V. Nalbandov. July, 1973. 57 p., index. Volume 31, Article 3.—Nutritional Respon- ses of Pheasants to Corn, with Special Reference to High-Lysine Corn. By Ron- ald F. Labisky and William L. Anderson. July, 1973. 26 p., index. BIOLOGICAL NOTES 78.—The Literature of Arthropods Associ- ated with Soybeans. II. A Bibliography of the Southern Green Stink Bug, Kezaro, viridula (Linneaus) (Hemiptera: Penta- tomidae). By N. B. DeWitt and G. L. Godfrey. March, 1972. 23 p. 79.—Combined Culture of Channel Catfish and Golden Shiners in Wading Pools. By D. Homer Buck, Richard J. Baur, Charles F. Thoits III, and C. Russell Rose. April, 1972. 12 p. 80.—Illinois Birds: Hirundinidae. By Rich- ard R. Graber, Jean W. XJraber, and Ethelyn L. Kirk. August, 1972. 36 p. 81.—Annotated Checklist of the Butterflies of Illinois. By Roderick R. Irwin and John C. Downey. May, 1973. 60 p. 82.—Lactate Dehydrogenase Isozymes ( Darters and the Inclusiveness of ti Genus Percina. By Lawrence M. Page an Gregory S. Whitt. May, 1973. 7 p. 83.—Illinois Birds: Laniidae. By Richard ] Graber, Jean W. Graber, and Ethelyn 1 Kirk. June, 1973. 18 p. 84.—Interactions of Intensive Cultures i Channel Catfish with Largemouth Bass i 1-Acre Ponds. By D. Homer Buck, Ricl ard J. Baur, and C. Russell Rose. Pe' ruary, 1974. 8 p. 85.—The Literature of Arthropods Assoc ated with Soybeans. III. A Bibliograph of the Bean Leaf Beetle, Cerotoma tt. furcata (Forster) and C. ruficornis (01 vier) (Coleoptera: Chrysomelidae). By 1 P. Nichols. M. Kogan, and G. P. Wall bauer. February, 1974. 16 p. 86.—Illinois Birds: Tyrannidae. By Ricl ard R. Graber, Jean W. Graber, an Ethelyn L. Kirk. February, 1974. 56 ] 87.—The Literature of Arthropods Assoc ated with Alfalfa. I. A Bibliography the Spotted Alfalfa Aphid, Therioaph maculata (Buckton) (Homoptera: Aph dae). By D. W. Davis, M. P. Nichols, an E. J. Armbrust. February, 1974. 14 p. 88.—The Literature of Arthropods Assoc ated with Alfalfa. II. A Bibliography ( the Sitona Species (Coleoptera: Curci lionidae). By W. P. Morrison, B. C. Pass, M. P. Nichols, and E. J. Armbrust. Feb- ruary, 1974. 24 p. CIRCULAR 46.—Illinois Trees: Their Diseases. By J. Cedric Carter. June, 1964. (Third print- ing, with alterations.) 96 p. 47.—Illinois Trees and Shrubs: Their Insect Enemies. By L. L. English. July, 1970. (Fifth printing, with revisions.) 91 p. 51.—Illinois Trees: Selection, Planting, and Care. By J. Cedric Carter. August, 1966. 123 p. 52.—Fertilizing and Watering Trees. By Dan Neely and E. B. Himelick. Decem- ber, 197^. (Third printing.) 20 p. 53.—Dutch Elm Disease in Illinois. By J. Cedric Carter. October, 1967. 19 p. List of available publications mailed on request No charge is made for publications of the Illinois Natur.\l History Survey. A single copy of most publications will be sent free to anyone requesting it until the supply becomes low. Costly publications, more than one copy of a publication, and publications in short supply are subjects for special correspondence. Such correspondence should identify the writer and explain the use to be made of the publication or publications. Address orders and correspondence to the Chief, Illinois Natural History Survey Natural Resources Building, Urbana, Illinois 61801