Bulletin STATE OF aUNOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE NATURAL HISTORY SURVEY STEPHEN A. FORBES. Chief Vol. XVI. BULLETIN Article II. Recent Insecticide Experiments in Illinois with Lubricating Oil Emulsions BY S. C. CHANDLER. W. P. FLINT, and L. L. HUBER PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA. ILLINOIS May. 1926 ERRATA Page 2, line 6, for loan read loam. Page 4, line 18 from bottom, beech (after water beech) should be followed by a semicolon. Page 138, line 10 and line 14 from bottom, for Dane read Dann. Page 139, line 5, for Dane read Dann. Page ISO, line 5 from bottom, delete D. Page 198, line 19 from bottom, for March read March 16, IfllS. Page 221, line 22, for data read date. Page 278, lines 17 and 18 from bottom in right-hand column, for ].'>0 read 158. Page 285, line 24 in left-hand column, for Franch read French. Page 321, table III, center column, for 1.02 read 1.00+ ; for l.OJ, read 1.02; for 1.06 read 1.0.',. Page 411, line 4, for pupation read breaking dormancy . STATE OF ILLINOIS -^JEPARTMKNT OP REGISTRATION AND EDUCATION A. M. Shelton, Director BOARD OP NATURAL RESOURCES AND CONSERVATION A. M. Shexton, Chairman WixiAM Tkelease, Biology Henry C. Cowles, Forestry Edson S. Bastin, Geology William A. Noyes, Chemistry John W. Alvoed, Engineering Kendric C. Babcock, Representing the President of the University of Illi- nois THE NATURAL HISTORY SURVEY DIVISION Stephen A. Porbes, Chief ScHNBTP & Barnes, Printers Springfield, III. 1926 49289—2500 CONTENTS PAGE Introduction 103 Experiments in Jolly orchard, Olney, III., spring of 1922 104 Experiments in University orchard. Olney, 111., winter of 1922-23 105 The theory of emulsion lOS The use of a solid as an emulsifier 106 The use of soap as an emul.sifier 106 Increa.se in volume of boiled emulsions 108 De-emulsiflcation 109 Combination of oil emulsion witli other materials Ill Comparison of boiled emulsions with lime sulfur and various miscible oils 112 Experiments in Hartline orchards, Anna, 111., winter of 1923-24. . . , 113 A comparison of oils for oil emulsion 119 A comparison of boiled fish-oil-soap emulsions and cold-mixed emulsions.. 119 Vegetable-oil-soap emulsions IZl Summer sprays with oil emulsion, 1923 and 1924 121 Experiments in Ed Kelley orchard, Anna, 111., winter of 1924-25 123 The effect of cold winters on San Jose scale and scale sprays 125 Summary and recommendations 125 I Article II. — Recent Insecticide Experiments in Illinois with Lu- bricating Oil Emulsions. By S. C. Chandler, W. P. Flint, and L. L. HUBER. Introduction From 1919 to 1922 inclusive, the San Jose scale caused more dam- age in southern Illinois than in any equal period since it was first estab- lished in this state. Following the work of Dr. Forbes and his assist- ants in 1900, 1901, and 1902, liquid lime-sulfur had been considered the standard remedy for San Jose scale control. Previous to 1919, it had not failed to give a satisfactory commercial control where thoroughly applied at dilutions of from 1 to 6, to 1 to 8. During 1920 and 1921, some of the best and most careful orchardists in southern Illinois lost trees from scale although these trees had been thoroughly sprayed with lime sulfur. In some instances the failure to control with it could be accounted for by the fact that the trees had been poorly sprayed, or an insufficient amount of material had been applied. In other cases, however, the applications had been made as thoroughly as seemed possible and enough material had been put on to cover the trees thoroughly. During the years mentioned above, a series of mild winters following warm late falls had allowed J;he scale to increase at an unusual rate, so that trees having a small amount of live scale remaining upon them in spring were heavily infested by fall. Because of the failure of lime sulfur to give a satisfactory control of scale, a series of experiments to test other scalecides was made by the Natural History Survey during the winter of 1922. These experiments were planned to give a comparison of com- mercial liquid and dry lime-sulfur with commercial miscible oils and homemade lubricating-'oil emulsions. The lubricating oil emulsion used, was of the type developed by W. W. Yothers, of the United States Bureau of Entomology for combating citrus scale insects in Florida, and was made by boiling together: Potash-fish-oil soap 1 pound Water ^ gallon Light grade lubricating oil 1 gallon The mixture was boiled for about five minutes, removed from the fire, and pumped twice under a pressure of about seventy-five pounds, and it was then diluted at the rate of three gallons of the stock emulsion to ninety-seven gallons of water. 104 Experiment in Jolly Orchard, Olney, Illinois, Spring of 1922 A block of twenty-five-year old Ben Davis and Grimes Golden apple trees was chosen for this experiment in what was known as the Jolly orchard at Olney. These trees were heavily infested, most of them having a considerable portion of the tree incrusted. Those selected for the ex- periment were divided into blocks five rows long by four rows wide, the center row being Grimes Golden, and the two outside rows Ben Davis. The infested branches, which were later cut for scale examinations, were taken from the inside rows of the blocks. The first sprays were applied on March 28, all blocks being treated within a week. Special attention was given to the application of the sprays. All trees were sprayed with rods, and the operator was followed by a third man to see that no part of the tree remained unsprayed. In the course of this work, we found that slightly more of the oil .sprays was required to cover trees of a given size than was the case with the lime sulfur sprays. For the twenty-five-year old trees, twenty gallons per tree of the oil were required and fifteen to seventeen gallons per tree of lime sulfur. Forty-seven days after the treatment, samples of scale- infested twigs were taken from various parts of the trees on the inner rows of all of the blocks and examined for living and dead scale. The re- sults of these examinations, expressed in percent of living scale, are shown in Table I. Table I Scalecide (1 to 15) Spray Emulsion (1 to 15) Diamond Paraffin oil, flsh-oll soap emulsion (2%).., Junior Red Engine-oil, fish-oil soap emulsion (2%). Commercial liquid lime-sulfur (32 Baume, 1 to 8) . • Soluble sulfur, Niagara (15 lbs. to 50 gals, water).. Dry lime-sulfur (15 to 50 ) Check, no treatment Percent of live scale .5 .4 1.5 7. 11. 18.5 41. 50. The following conclusions, standing in the order of their import- ance, may be noted : 1. The oil sprays were superior to the sulfurs. 2. The oil emulsion made from Oil No. 1, the brand used in most cases in Florida, was almost as effective as the miscible oils. 3. Dry lime sulfur was not as good as liquid lime sulfur. The fact that even after the most careful spraying, 11% of the scale was still alive on trees treated with lime sulfur, explained the failure of some growers to control scale where this material had been used. No further experiments were made in this orchard during 1922, but the remainder of it was sprayed thoroughly with commercial lime sulfur, used at 1 to 6, and in some cases at 1 to 4, dilution. 105 By fall of that year, the scale had so increased that but little fruit in the orchard was salable, and in the spring of 1923, the orchard was so badly infested by scale that no further attempt was made to save the trees by spraying. On May 4 of that year, however, the only trees of the orchard which were blooming, and practically the only trees alive, were those which had been given the oil sprays the previous spring. These blocks of trees were in a fairly vigorous condition, while practically all of the lime-sulfur sprayed trees around them were dead. The entire orchard was cut down during the next year because nearly all the trees had been killed by San Jose scale. ( See Fig. 1 and 2.) 106 Most formulae for oil emulsions have been the result of practical experience, for we know but little in regard to the various theories involved in a study of colloids, but some knowledge of the theory of emulsification is necessary if we would proceed intelligently. THE THEORY OF EMULSION The theory of emulsion is based on the assumption that we are dealing with two-phase systems, the oil and the water being the re- spective phases. The oil is the disperse or internal phase, the water is the continuous or external phase, and the two phases of the system are separated by surfaces of contact, or interfaces. The external phase may be either a solid or a liquid. The first part of this discussion is concerned with a system in which both phases are liquids ; but the latter part, with a system in which one phase is a liquid and the other a solid. An emulsion is defined by Clayton as a system containing two liquid phases, one of which is dispersed as globules in the other. Mak- ing lubricating oil emulsion is essentially a mechanical process which has for its purpose the breaking up of the oil in the water, but as oil and water are immiscible an emulsifying agent is needed, and here again there may be two kinds of emulsions, "oil in water" and "water in oil", depending upon the nature of the emulsifying agent. The lubricating oil emulsions are of the former kind. THE USE OF A SOLID AS AN EMULSIFIER It has been long known that any substance that will go into the interface and thus increase viscosity, will cause emulsification. In other words, the insoluble solid, if finely enough divided, will yield results similar to those produced by a gelatinous colloid, such as soap. Picker- ing was one of the first to point out that the basic sulfate precipitated in Bordeaux mixture consists of just such particles. These particles have only a slight tendency to unite with one another, and are more readily wetted by water than by oil. When the oil is added to the Bordeaux mixture and broken up by agitation, the finely divided pre- cipitate surrounds the oil globules, thus holding them in suspension. Theoretically there seems to be no reason to ex])ect unfavorable results with the soapless emulsions. Indeed, in instances where a weak Bor- deaux is advised when the soap emulsions are to be diluted with hard water, we get, in reality, what amounts to a soapless Bordeaux-oil emulsion. THE USE OF SOAP AS AN EMULSIFIER Bancroft holds that if the emulsifying agent is such that it will lower the interfacial tension of the water more than that of the oil so that the film bends convex to the oil, there will be a tendency to emulsify the "oil in water," but if the absorption of the emulsifying 108 agent brings about an opposite condition, a "water in oil" emulsion will result. Hence, to make an "oil in water" emulsion it is necessary to use a water-soluble colloid ; and to make a "water in oil" emulsion an oil- soluble colloid must be used. More briefly still, to get an "oil in water" emulsion the emulsifying agent must be such that it is wetted more by water than by oil. Potash and sodium soaps are such water-soluble colloids. The excellence of an emulsion is judged primarily by its stability, which is very dependent on its viscosity. Upon what then does the vis- cosity depend? Possibly the greatest single factor affecting viscosity is the volume ratio of the oil and water, or the concentration of the oil. While it is possible to make an emulsion with potash-fish-oil soap and oil alone, or by the addition of an unusual amount of water to the oil and soap, experi- ment has shown that there is an optimum proportion of ingredients. Another factor affecting viscosity is the degree to which the in- gredients are mechanically agitated. Orchardists have noted that the more often the mixture is run through their pumps and the greater the pressure, the more viscous is the product. This is due to the fact that the oil is reduced to more minute globules and the extent of the oil-water surface is thus greatly increased. A deficiency in the proportion of soap results in lower viscosity owing to the prevalence of larger oil globules, regardless of agitation. These large globules have a tendency to coalesce by breaking the film which surrounds them. The size of the oil globules is further dependent on the tempera- ture of the mixture when it is agitated. A cold mixture will yield an emulsion physically inferior to a hot mixture. However, field and laboratory tests have demonstrated that there is nothing to be gained by continued application of heat. Heating facilitates emvilsification only by lowering the viscosity of the mixture and reducing the interfacial ten- sion between the two phases, thus aiding mechanical agitation. In comparative spray-tests we have often failed to take proper cognizance of the fact that an emulsion undergoes some quantitative changes during the process of manufacture. Unless these changes are taken into consideration there is apt to be an element of doubt as to the accuracy of our results. In this regard, it is well to keep in mind that a mixture may, or may not, increase in volume with emulsification. INCREASE IN VOLUME OF BOILED EMULSIONS In making up the large series of emulsions which was necessary for these experiments, it was noticed that there was a greater increase in volume in the case of some boiled emulsions than in others, although exactly the same proportions and length of time for boiling was allowed in all cases. In one case the volume was increased by 13%, even though the outlet hose was put into the liquid so that large amounts of air 109 could not be mixed with the emulsion. The increase was much greater where the hose was held out of the liquid, allowing the discharge to fall through the air. In most cases, this increase in volume is not very significant after the emulsion has cooled. The grower making his own emulsion should bear this point in mind when he comes to the dilution of his product. The data of the tables tend to prove that the amount of water and soap as well as this increase in volume are factors to be considered if final results are to be used in a comparative way. Table II 1. Formula: Oil 1 gallon, water % gaUon, soap 2 pounds Emulsion. 110 Perhaps the most common source of de-emulsification is the presence of calcium or magnesium in the water that is used as a diluent. The presence of these salts with the oil leads to the formation of an insoluble calcium or magnesium soap, which are products of reversion and tend to form "water in oil" emulsions. The addition of Bordeaux mixture to the diluted spray solution prevents this reaction. This recommenda- tion is based upon a statement made in the fore part of the discussion, that a colloid solution has two phases—a solid and a liquid. A fuller explanation is given in the following paragraphs. Although emulsions can be made with even extreme amounts of water or soap, there is a practical optimum amount of each of these constituents. Judging from our experiments, the optimum amount of soap is from one to two pounds per gallon of oil, and that of water from % to y2 gallon for each gallon of oil. It has been found neces- sary, in order to get a good emulsion, to use from 1 J/2 to 2 pounds of soap with many of the waters used by orchardists for spraying in this state. Emulsions made with varying amounts of soap and water were tested as to their ability to kill scale. The following tables show the results. Table III Strength of oils Ill I COMBINATION OF OIL EMULSION WITH OTHER MATERIALS For practical reasons, it is desirable that a spray may be mixed with as many other spray materials as is possible. Obviously, it is highly desirable that Bordeaux mixture, a fungicide, should be one of the com- patible sprays. As already indicated, any substance that will go into the interface and increase the viscosit)' will cause emulsification, and the basic sulfate which is precipitated when lime and copper sulfate are poured together, does exactly this thing. The small particles of the pre- cipitate have only a slight tendency to unite with one another and are more readily wetted by the water than by the oil ; hence they surround the oil globules in the spray solution, thus aiding the soap in holding them in suspension. Pickering, in IflOT, discovered that oil could be emulsified with Bordeaux mixture. Some of his work was therefore duplicated in 1922 in our laboratory, and the product tried out in the field the following year. Since such a combination is theoretically and practically sound, an oil emulsion made by the formula, one gallon paraffin oil, 90 vis- cosity, one-fourth gallon of water, and two pounds of potash-fish-oil soap, was used at varying strengths with Bordeaux mixture at strengths of 3-9-50, 9-3-50, and 4-4-50. The results are shown in Table V. 112 Table VI Treatment 113 Table VII gives the results of applications of lime sulfur and of various miscible oils. Since these were applied in the same manner as the oil emulsions mentioned in Tables II to VI inclusive, an inspection of those tables will also give a comparison with the homemade emulsions. Percent of oil in emulsion 114 that some of the fall sprays were repeated in spring. In most cases this was done to check up on fall applications which showed an appreciably higher percent of live scale than did oil emulsion made with a certain 90 viscosity paraffin oil, which we use as a standard because of the large number of tests which have been made with it. In Table IX, viscosity was ascertained by the Saybolt test. Good emulsions were obtained with all the oils used. I 115 3 m Ml % c £ S t- c ol Q 116 la "S > (1) 4J s s a-* SI si a n? I ^ 118 119 A Comparison' of Oils for Oil Emulsion Good emulsions were made with all grades of oil used, but five of them show a somewhat too high percent of live scale in the fall tests. Comparing the scale kill with the analyses of oils, it will be found that the most effective oils fall within certain limits. After a conference with government entomologists who had been working on the control of San [ose scale with oil emulsions at Bentonville, Arkansas, and at Vincennes. Indiana, and with the Entomologist of the Purdue Agricultural Ex- periment Station, a joint statement was issued in the fall of 1924 to the effect that the best results had been obtained with oils within the following limits : Specific gravity 87 to .93 at 20° C. Volatility Not above 2% at 110° C. for 4 hours. (Saybolt test.) Viscosity 90 to 250 seconds at 100° F. (Saybolt test.) A Comparison of Boiled Fisii-oil-Soap Ejiulsioxs AND Cold-mixed Emulsions 1. Scale Kill Table X, summarizes all the tests made in the Hartline orchard with boiled fish-oil-soap emulsions of 2% strengths and all those with cold- mixed emulsions except where lime sulfur was combined with them. This table shows the cold-mixed emulsions to be not quite so effective as the boiled emulsions. This table, however, gives only a rough com- parison of all types of cold-mixed emulsions used with certain types of boiled emulsion. Type of emulsion 120 J. Ease of Dilution The ease with which any spray material mixes in the tank is an im- portant consideration. Some stock emulsions look good, but upon dilu- tion with water, free oil, which may be injurious to plants, appears on the surface. In the case of the cold-mixed emulsions with Bordeaux mixture as the emulsifying agent, the stock emulsion rises to the top of the spray solution, though no free oil may appear. This difficulty can be overcome by diluting the stock emulsion with a weak Bordeaux instead of water. A 1-1^-50 Bordeaux holds it at an equilibrium. It is possible that with the agitator in a spray tank running, this difficulty would not be so serious, but the stock emulsion rises quickly, and it is not at all certain that with the agitator in the bottom of a full tank, a good mixture could be made. 4. Stability On the whole, cold-mixed emulsions are not as stable as boiled emul- sions, as shown by our experience of the past four years. The cold- mixed stock emulsions, upon standing, break down faster than the boiled emulsions, especially in cold weather. For this and other reasons, there is a greater likelihood of injury with the cold-mixed emulsions than with the boiled emulsions. 5. Conipatibilitv with Fungicides The boiled soap-oil emulsions will mix with Bordeaux, but not with lime sulfur. Most cold-mixed emulsions will mix with both Bordeaux and lime sulfur. \Miile there is some precipitation in the cold-mixed emulsions with lime sulfur, yet effectiveness does not seem to be impaired, as will be seen by applications 69 and 70 in Table IX (pp. 115, 117). 6. Kinds of Cold-mixed Emulsions and Methods of Making Bordeaux.—Cold-mixed Bordeaux-oil emulsion is made by pumping together, without heating, oil and Bordeaux mixture. Most of that used in our experiments Was made with equal parts of oil and Bordeaux. Three pumpings gave a product appreciably better than that made with two. In most of our work, a 4-6-50 Bordeaux (using hydrated lime) was used. Calcium Caseinate.—Kayso, or any form of calcium caseinate, usually makes a good emulsion. It is probably the easiest to make of any of the commonly used cold-mixed emulsions, and one of the cheapest. The formula generally used is two gallons of oil and one gallon of water in which is mixed four ounces of calcium caseinate. Calcium ca.-^einate should be used fresh to get the best results. Iron Sulfate-Limc.—Iron sulfate and lime can be used in place of the copper sulfate and lime of the Bordeaux mixture. In our experi- 121 ments, this emulsion was made up in exactly the same way. The same difficulty of the emulsion rising to the top appeared, but was overcome by diluting with a 1-1J4-50 iron sulfate-lime mixture instead of water. Colloidal Clays.—Certain colloidal clays—Kaolin, Fuller's earth, Bentonite, and several others—have been used successfully for making cold-mixed oil emulsions. Those made with these clays were only tested in a very limited way in the work here recorded, but very good results were obtained. Work of the entomologists of the Bureau of Entomology and in other states indicates that excellent emulsions can be made with these colloidal clays. In some respects these are superior to most other types of cold-mixed oil emulsions, and they are much cheaper than the boiled soap oil emulsion. They are made up in the form of a thin paste rather than a fluid, and this is objectionable for some uses. VEGETABLE-OIL-SOAP EMULSIONS In treatments Nos. 54, 53, 56, 80, 81, and 83 of Table IX (see p 115), the results of spraying with emulsions made with vegetable-oil soap as a substitute for fish-oil soap are given. They are apparently just as effective scalecides as the emulsions made with potash-fish-oil soap, and are slightly cheaper. Summer Sprays with Oil Emulsion, 1923 and 1921 foliage tests, summers of 1923 and 1924 Oil emulsions had, of necessity, been used for a number of years on citrus trees while in foliage. During the summer of 1932, they were used on apple foliage with little or no burning in experimental work by the Bureau of Entomology in the Bentonville, Arkansas, section, and in work done by this office near Olney, Illinois. During the summer of 1923, foliage injury tests were made at Carbondale with a number of diflerent trees, shrubs, and other plants. Apple, cherry, grape, lilac, mul- berry, maple, peony, peach, pear, potato, rose, tomato, and walnut were sprayed during June on clear hot dry days, the temperatures ranging from 89° to 91° F., with 2% strengths of (1) boiled fish-oil-soap emul- sion, (2) the same with Bordeaux mixture, 4-1-50, and (3) cold-mixed Bordeaux oil emulsion, and the only seen injury to plants in these tests was severe burning of the foliage on potato and tomato, and a slight blackening of a few leaves on rose and maple. On cooler cloudy and humid days, with temperatures ranging from 80° to 83°, the following were injured. With boiled fish-oil-soap emidsion alone Peach Slight to defoliation Pear 50% of leaves specked black Tomato 15% of leaves partly blackened Rose 40% of leaves slightly burned Walnut 50% of leaves peppered with black dots Maple 2% of leaves slightly blackened 122 With boiled fish-oil-soap emidsion in 4-4-50 Bordeaux Peach Same as on p. 121 Pear V/i of leaves slightly burned Walnut Same as on p. 121 Maple 25% of leaves injured With cold-mixed Bordeaux-oil emulsion Peach Same as on p. 121 Pear 90% of leaves burned, 15% severely, 8% killed Tomato 10% of leaves partly blackened Rose 50%. of leaves burned Walnut Same as on p. 121 Maple 10% of leaves burned severely During the summer of 1924 the following sprays were confined to apple, cherry, grape, peach, plum, potato, and tomato. Boiled fish-oil-soap emulsion alone, 1% and 2% with paraffin oil of 90-100 viscosity. Boiled fish-oil-soap emulsion, plus Bordeaux 4-6-50. Boiled fish-oil-soap emulsion, plus Bordeaux 4-6-50, and ar- senate of lead 2-50. All the above repeated, using a paraffin oil of 212-220 viscosity. Calcium caseinate cold-mixed emulsion, 1% and 2% with oil of 90-100 viscosity. Skim milk cold-mixed emulsion, 1% and 2% with oil of 90-100 viscosity. The injury, listed according to plants sprayed, was as follows : Apple, Cherry, Grape. . .No injury by any spray under any con- dition of weather. Peach From 30% to 90% defoliation with boiled fish-oil-soap emulsion, 90 vis- cosity, paraffin oil at 2% strength with and without the addition of Bordeaux and arsenate of lead. This occurred both in hot dry weather, and in cooler, cloudy, humid weather. Only slight injury with 1%. Using 1% with oil of 212-220 viscosity, no defoliation was observed. No injury with the cold-mixed emulsions. Plum No injury. Potato 2% strengths of everything except the milk emulsions, gave moderate to se- vere burning. l^J strengths pro- duced very little burning, and usually none. 123 Tomato In most cases injured moderately to se- verely, both the leaves and fruit, by both 1% and 2% applications. The apples used in these tests were Winesaps, in the nursery row. Larger trees in the University orchard at Olney were sprayed with the regular orchard equipment in the summer of 1923 by the Horticul- tural Department of the University of Illinois. On apples receiving from one to three summer applications, very slight burning of the foliage was seen in all blocks, but nothing serious. Dr. B. A. Porter, using summer sprays on various varieties of apples at Vincennes, found injury serious only on Grimes Golden. Scale Tests zv-ith Oil Emulsion, Summer of ip2j Three series of tests were made during the summer of 1923 with 2% strengths of (1) boiled-fish-oil-soap emulsion; (2) boiled fish-oil-soap emulsion, with Bordeaux; and (3) cold-mixed Bordeaux-oil emulsion. In these experiments, the leaves were all removed from the sprayed branches so that every scale could be hit ; and reinfestation was pre- vented, as far as possible, by bands of tanglefoot around the bases of the branches. In the first two of these series, the percent of scale found alive upon examination ranged from .2fc to 2.5%. In an ad- joining orchard which was being sprayed with a 3% strength of oil emul- sion during the time of one of the tests, 16.8% of the scale was found alive, showing the effect of the foliage in preventing thorough applica- tion, and indicating that under orchard conditions, summer applications would not be very effective. The third series of tests gave 15% of the San Jose scale alive, even where the foliage was removed so that every scale was hit. Experiments in Ed Kelley Orchard, Anna, Illinois, Winter of 1924-25 During the winter of 1924-25, a series of tests was run with the object of comparing the efficiency of light and heavy oils when used in boiled and cold-mixed emulsions. All applications were made with the hand sprayer, as previously described. The fall sprays were applied December 1-9, and examined from six to eight weeks later for live scale. The spring application was made February 7, and examined six weeks later. Table XI gives the results of these sprays. 124 Table XI Treatment (Oil emulsions, all at 2% strength) 125 The Effect of Cold Winters on San Jose Scale AND Scale Sprays All examination of the foregoing tables will show considerable vari- ation from year to year in winter mortality. The counts of live scale for the four years on untreated branches were as follows : Year Percent alive 1921-22 50.4 (March) 1922-23 65.9 (April) 1923-24 41.4 (March) f29.3 ( Tanuarv) 1924-25 -{13.0 (February) [lO.O (March) It would seem entirely plausible that with the weakening effect of a cold winter on scale, the sprays would be more effective. The tables pre- sented here seem to indicate that this is true. In the fall tests in 1923, given in Table VTII, the percent of live scale runs higher than in the spring tests (1924) given in the same table. During this season we had a rather unusual experience in making scale counts. Previously, after applying sprays, a month had been found long enough to wait for the drying up of the scales that had been killed. Following the fall applications of this year, however, there was a period of abnormally cold weather, and on starting our counts after the usual interval, the oil-sprayed branches showed from 22 to 36 percent of the scale apparently alive. After another four weeks, branches with the same treatment showed only 1.3% to 1.8% live scale, indicating that the scales had been kept in cold storage, as it were, the continuous cold preventing their drying sufficiently to show any discoloration. The win- ter of 1924-25 was the most severe on the San Jose scale of any winter since 1917-18, and the record of only lO'/i live scale on the check branches in southern Illinois in March is remarkably low. The effect of this win- ter-killing is indicated by the very small percent of live scale shown in Table XI for that year, in which none of the treatments, with the excep- tion of two very poor emulsions, gave less than 99% dead scale. SuMMARV and Recommendations This report gives the results of four years experiments on the con- trol of San Jose scale at various points in southern Illinois. The superiority of oil sprays over lime sulfur was demonstrated, 11% of the scale remaining alive after being hit with lime sulfur, as compared with less than 2% with most of the oil sprays. Boiled emulsion was as effective as the various miscible oils used. Cold-mixed oil emulsions were about as effective as the boiled emul- sions, but somewhat more unstable. The most reliable type of homemade emulsions are the boiled soap- emulsions. 126 Vegetable-oil soap was as effective in making the boiled emulsions as fish-oil soap. Emulsions made from oils with viscosities below 80, have not shown uniformly good kill of scale. There were apparently no differences in effectivness on San Jose scale in emulsions made from oils of 90 to 220 viscosity. Tests with boiled potash-fish-oil-soap emulsions in summer showed very little injury to apple foliage, considerable injury to peach, and to a few other plants under some conditions. Due to the difficulty in reaching the scale when the trees are in foliage, summer sprays are not recom- mended except in case of very severe scale infestation. Where oil emulsions were properly mixed and applied, no injury to trees has resulted. On the basis of these experiments and observations, the following recommendations are made : 1. Oil emulsion is recommended as a cheap and effective spray for the control of San Jose scale. The formula for the stock emulsion found best in our experimental work is as follows : Oil 1 gallon Potash-fish-oil-soap 1 to 2 pounds Water Ya gallon Heat to boiling, and pump twice at a pressure of 75 pounds, or more. The strength recommended is 2.4% (3 gallons in 100), or, in case of se- vere and increasing infestation, 4 gallons in 100 gallons of water. The best oil to use, judging by our experiments and those of investigators in Indiana and Arkansas, is a lubricating oil coming within the following limits : Specific gravity.. .87 to .9,3 at 20° C. Volatihty Not above 2% at 110° C. for 4 hours. Viscosity 90 to 250 seconds (Saybolt test) at 100° F. 2. If cold-mixed emulsions are used, they may be made according to the following formulae:— • Bordeaux, Cold-mixed Pump together equal parts of oil and 4-4-50 Bordeaux mixture, sending the material at least three times through the pump. For a 2% strength, dilute four gallons in one hundred. Calcium Caseinate, Cold-mixed Pump together two gallons of oil and one gallon of water in which is dissolved four ounces of calcium caseinate. For a 2% strength, use three gallons in one hundred.