Maataloustieteellinen Aikakauskirja Vol. 62: 339—347, 1990 Conventional and organic cropping systems at Suitia V: Cereal diseases ASKO O. HANNUKKALA 1 and EEVA TAPIO2 1 Institute of Plant Protection, Agricultural Research Centre SF-31600 Jokioinen, Finland 2 Department of Plant Pathology, University of Helsinki SF-00710 Helsinki, Finland Abstract. The occurrence of diseases on barley and winter wheat was surveyed in a field experiment comparing four conventional and four organic cropping systems in 1982—88. On barley, foliar diseases were of minor importance regardless of the cropping system. On winter wheat, powdery mildew (Erysiphe graminis), yellow rust (Puccinia striiformis) and leaf blotch (Septoria nodorum) were more prevalent in conventional than in organic cropping systems. Root and foot rot diseases (Bipolaris sorokiniana, Fusarium spp. and Gaeumannomycesgrami- nis) were frequent on barley and winter wheat in each cropping system. B. sorokiniana in- fected stem bases and roots of barley more frequently in organic than in conventional crop- ping systems. During the first years of the study, a serious epidemic of G. graminis was recorded in certain organic cropping systems. Index words: Hordeum vulgare, Triticum aeslivum, cropping systems, Erysiphegraminis, Puccinia striiformis, Sep- loria nodorum, Fusarium avenaceum, Fusarium culmorum, Cochliobolus sativus, Gaeumannomycesgraminis, foliar diseases, root rot, foot rot, cereals Introduction Control of diseases in organic farming is primarily preventative rather than curative. Giving up fungicides makes organic cropping systems vulnerable to certain diseases, espe- cially during the conversion period. Diseases can be controlled by carefully planned, diverse crop rotation, balanced nutrient supply and by use of resistant varieties (Marland 1989). In 1982, when the present study was started, seed dressing was the only widely adapted means of chemical disease control on spring sown cereals in conventional farming in Fin- land (Tiittanen and Blomqvist 1983). Seed treatment is mainly targeted against loose smut (Ustilago nuda (Jens.) Rostrup f.sp. hordei Schaffnit and U. nuda (Jens.) Rostrup f.sp. tritici Schaffnit), barley stripe (Pyreno- phora graminea Ito & Kuribay.) and seedling 339 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=7qwer7tjXGWD4DK_.pVj_1ZLydHFBjapGrkrxVg.-oP-USXUsJKEd6HHN92a68h_4SZUW1AhFIfQmLjvbwEW_Nqo9jt6uFnJWi6y1rOUOqYdvP_K-DovviVK2cmAQlFb1hcHwvpsLB7l5GLXwjkhpQ9m5iacz00dgncf7EivY7NPvK1oDBr3Lob8yLQWPM1-LnUmPwEFQkXX7kUh73LYQbQ2QpO6GGHj9hpZgcI blights (Fusarium spp. and Bipolaris soro- kiniana (Sacc.) Shoem.), teleomorph Cochlio- bolus sativus (Ito & Kuribay.) Drechsl.: Dast.) (Vanhanen 1981). In the 1980s, leaf infecting diseases, pow- dery mildew (Erysiphe graminis DC.: Merat) on barley and wheat, leaf blotch (Septoria nodorum (Berk.) Berk) on wheat, net blotch (Pyrenophora teres Drechsl.) and scald (Rhyn- chosporium secalis (Oud.) J.J. Davis) on bar- ley have caused considerable damage in Fin- land (Kurtto 1986). In conventional farming they are controlled by fungicides. Also, moderately resistant cultivars are available. Soil-borne root and foot rot diseases, B. sorokiniana, Fusarium culmorum (W.G. Sm.) Sacc., F. avenaceum (Fr.) Sacc., (teleomorph, Gibberella avenacea R.J. Cook), Gaeuman- nomyces graminis (Sacc.) von Arx & Olivier and Rhizoctonia spp., are common especial- ly in conventional cereal-intensive cropping in Southern Finland (Mäkelä and Parikka 1980). They are controlled by seed dressing, crop rotation and management of energy resources in soil (Garret 1970). Organic amendments to soil increase the microbial ac- tivity, thus frequently decreasing soil-borne diseases. Cereal root rot pathogens are able to colonize organic substrates incorporated into soil, which is occasionally reported to in- crease their inoculum potential (Linderman 1989). Very few studies comparing conventional and organic farming systems deal with disease problems (Lampkin 1986). The objective of this study was to survey cereal diseases in different conventional and organic cropping systems (Hannukkala et al. 1990), with spe- cial emphasis on foot and root rot diseases. Material and methods Diseases on barley and wheat were surveyed in a field experiment comparing four conven- tional and four organic cropping systems. The conventional cropping systems were managed with high chemical inputs, while no chemical fertilisers or crop protection were allowed in the organic cropping systems. The detailed ex- perimental design is given by Hannukkala et al. (1990) pp. 295—307 in this issue. The crop- ping systems, outlines of their fertilisationand the symbols used in the text and tables are: Conventional cropping Al = barley monoculture, N-P-K fertilisation A 2 = cereal production, N-P-K fertilisation A 3 = diverse plant production, N-P-K fertilisation B = cattle farm, N-P-K fertilisation and slurry Organic cropping Cl = plant production, plant material composted C 2 = plant production, plant material not composted Dl = cattle farm, slurry composted D 2 = cattle farm, slurry not composted The occurrence of diseases on barley was studied in 1982, 1985 and 1988, when barley was grown in all cropping systems. Diseases on winter wheat were surveyed in 1983 and 1986, respectively. The incidence of smuts and of foliar diseases was checked visually every second week until growth stage 83 (Zadocks et al. 1974). If more than approximately 1 % of plants had symptoms on their leaves, a ran- domized sample of 50—100 plants was col- lected from each plot. The diseased leaf area of three upper leaves of individual plants was estimated using the assessment keys of James (1971). The occurrence of root and foot rot diseases was analysed at growth stages 75 (milk stage) and 95 (harvest) (Zadocks et al. 1974). A ran- domized sample of 50—200 plants was col- lected from each plot. Plants were washed un- der running tap water and rated for disease. Stem bases were classified healthy, lesioned and brown/black. The root rot severity assess- ment was based on the percentage of dis- coloured root-area in the uppermost 5 cm of the root system. Plants were classified in six 340 categories according to the method of Jensen and Jorgensen (1973): 0= roots without dis- coloration; I=o.l—lo <7o; 2 = 11—25 %;3 = 26—50 %; 4 = 51—75 %; and 5 = 76—100 °/o discoloured root mass. The root rot severity (RS) was finally calculated with the formula: DC OxNO+lxNl+ 2xN2+3xN3+4xN4+sxNs„ ln„ Kj= X IUU 5x(NO+Nl + N 2 + N 3 +N4+N5) where NO to N 5 are numbers of observations in each category. Diseased stem bases were cut into pieces about 2 cm long. They were surface sterilised for 1 minute in 1 % sodiumhypochlorite (NaOCl) solution, 10 seconds in 96 % ethanol and rinsed with sterile distilled water. Surface sterilised stem pieces were left to dry for 3—4 hours and transferred to CMA (Cornmeal agar, Difco Laboratories, Michigan, USA) to which 200 ppm streptomycin sulfate was added to inhibit bacterial growth. Plates were incubated at room temperature (18 —20°C) at diffuse daylight and examined for fungal iden- tification after 7 and 20—25 days. When necessary, tips of fungal hypha were trans- ferred to PDA (Potato dextrose agar, Difco laboratories, Michigan, USA) for further identification. To identify the fungi inhabiting the root sys- tem, a randomized sample of 50 root pieces about 1 cm long was taken from plants after disease rating. Root pieces were surface steri- lised, transferred to CMA, incubated and ex- amined as described above. In 1985 and 1986, an additional root sample (50 root pieces/plot) was surface sterilised as above and transferred to media selective to Bipolaris sorokiniana (Reis 1983). Another additional sample of 50 root pieces/plot was surface sterilised with sil- ver nitrate solution (1 % AgNO s) according to the method of Stetter and Leroul (1979) and incubated in media selective for Gaeu- mannomyces graminis (Juhnke et al. 1984). The germination of harvested seed and fun- gi associated with germinated and ungermi- nated seed was analysed by a blotter test (de Tempe 1963). 4 The experimental data were analysed using SPSS Inc. and SAS Institute Inc. statistical packages. The complete model for testing differences between means and frequencies consisted of four main factors: group of crop- ping systems (conventional vs. organic crop- ping), individual cropping systems nested within group (treatment), year (repeated ob- servation) and replicates (blocks) (Hannuk- kala et al. 1990). Individual cropping sys- tems were often ignored, and the final model included three main factors: group of crop- ping systems, year and replicate. The models were tested either using the analysis of vari- ance procedure and the Tukey test or the max- imum likelihood method to estimate param- eters for log-linear models (CATMOD-pro- cedure for categorical data modeling, SAS In- stitute Inc.), depending on the type of data. Results Diseases on barley Seed-borne diseases, loose smut and barley stripe, were detected in the experiment only occasionally. The average numberof diseased plants was less than 1 per 10square metres in all cropping systems. The seed harvested from conventional cropping systems germinated well. In organic cropping systems, the percent- age of normally germinated seed was consider- ably lower in 1985 and 1988, which indicates high infestation of seed with B. sorokiniana (Table 1). There was only a trace of foliar diseases in years when barley was grown in all cropping systems: net blotch and scald were found oc- casionally regardless of the cropping system. In 1984, stem rust (.Puccinia graminis Pers.) and brown rust (Puccinia recondita Rob.: Desm.) attacked barley late in the growing sea- son. At growth stage 75, 42 % of stems were infected. In 1987, when barley was grown only in conventional cropping systems, there was a heavy attack of net blotch. On the average, 35 % of barley plants showed symptoms on stem bases. In 1982, 341 Table 1. Germination and pathogenic contamination of harvested barley seed in conventional and organic crop- ping. Conventional Organic Statistical cropping cropping significance Year Normally germinated barley seed % 1982 97 96 NS 1985 90 81 *** 1988 91 78 *** Pathogens: Pathogenic contamination of seed % Bipolaris sorokiniana 6 19 *** Fusarium spp. 38 19 *** Table 2. Occurrence of foot rot and foot rot pathogens, Bipolaris sorokiniana, Fusarium avenaceum and F. culmo- rum, on barley in conventional and organic cropping systems at growth stage 75 in 1982, 1985 and 1988. Cropping Year 1985 1988 Mean system (CS) 1982 % of plants with foot rot symptoms Conventional (C) 40 29 68 46 Organic (O) 54 34 47 45 % of diseased stem bases infected with B. sorokiniana Conventional (C) 13 12 8 11 Organic (O) 39 40 23 34 % of diseased stem bases infected with F. avenaceum and F. culmorum Conventional (C) 31 9 97 46 Organic (O) 33 15 74 41 Chi-squares for factors included in the best log-linear model: variable: foot rot % B.sorok. % Fusarium % Year (Y) 316.2 *** 24.2 ••• 253.0 *** Group of cropping systems (GCS) 0.4 ns 160.6 •*• 10.6 * Interaction YxGCS 249.5*** 37.1 *** foot rots were more common in organic than in conventional cropping (x ! = 206.03***); in 1985 there was no statistically significant difference between cropping systems (x 2 = 6.87), while in 1988, stems in organic crop- ping were healthier than in conventional crop- ping (X 2 = 113.07***). Common root rot pathogens, Bipolaris sorokiniana, Fusarium avenaceum and F. culmorum were isolated from diseased stems. B. sorokinianawas more frequent in organic than in conventional crop- ping. In 1988, Fusarium spp. were more fre- quent in conventional than in organic crop- ping (x 2 = 36.60***) (Table 2). Gaeumanno- myces graminis and Rhizoctonia spp. were found to some extent in 1982, but they were very rare in 1985 and 1988. In 1988, Michro- dochium nivale (Fr.) Samu & Hall (Gerlachia nivalis (Ces.: Sacc.) W. Gams& E. Milli.) was found occasionally. The root rot severity measured as root dis- coloration was clearly affected by the group of cropping systems in 1985 and 1988 but not in 1982. In 1985, roots were healthier in con- ventional cropping, while in 1988 they were healthier in organic cropping. No differences in root discoloration between individual crop- ping systems within organic or conventional cropping could be shown (F-values 1982: 1.68 ns, 1985: 1.78 ns, 1988: 4.07*) (Table 3). Statistically significant differences in root dis- coloration between replicates were found (F- -value 5.97***). Essentially the same pathogens were iso- 342 Table 3. Root rot severity (0 —100) and number of Bipolaris sorokiniana, Fusarium spp. and Gaeumannomyces graminis per m of root of barley in conventional and organic cropping at growth stage 95 in 1982, 1985 and 1988. Group of cropping Year 1985 1988 Mean systems 1982 Root rot severity (0—100) Conventional 27a 23" 14a 21 A Organic 30" 33" 5" 22 A Number of B. sorokiniana infections per m root Conventional 25a 50a 2a 26A Organic 64b 94b 15b 57 B Number of Fusarium spp. infections per m root Conventional 65" 65a 9a 46A Organic 73» 61" 16» 50A Number of G. graminis infections per m root Conventional 16a 27a 7 a 16A Organic 36 b 23a 4 a 21 A Means with the same letter do not differ statistically (p = 0.005) "_b comparison of two means within one year A-B comparison of grand means of cropping system lated from roots as from stem bases. The number of B. sorokiniana infections was con- siderably higher in organic than in conven- tional cropping each year (F-values 1982: 54.32***, 1985: 110.02***, 1988: 28.90***). The roots were most severely infected in the cropping systems C 2 and D2, where uncom- posted plant material was applied (Fig. 1). Yearly variation in the number of Fusarium spp. and G. graminis infections was consider- able (F-values 379.57*** and 54.97***, re- spectively). The highest counts for both fungi were recorded in 1982 and 1985. Cropping sys- tems usually had no statistically significant effect on the occurrence ofFusarium spp. and G. graminis. However, in 1982, G. graminis was recovered twice as often on roots in or- ganic as in conventional cropping (F-value 7.l4***) (Table 3). Diseases on winter wheat 65. The mean leaf area covered by the patho- gen was approximately 0.5 %. In organic cropping systems, less than 5 % of plants had mildew on one of the three upper leaves (Fig. 2). In 1986, leaf blotch and rusts (Puccinia strii- formis Westend. and P. recondita) were com- mon in winter wheat, while powdery mildew was of minor importance. The average per- centage of plants with one of the three upper Loose smut and other primarily seed-borne diseases were rare in all cropping systems. In 1983,powdery mildew attacked winter wheat in conventional cropping systems, where more than 50 % of plants had symptoms on at least one of the three upper leaves at growth stage Fig. I. Occurrence of common root rot (Bipolaris sorokinicma) on barley roots in conventional and organic cropping systems at growth stage 95 in 1982—88. Bars with the same letter donot differ statistically (p=0.005). 343 leaves infected with leaf blotch and yellow rust was higher in conventional than in organic cropping systems. Leaf blotch was most prevalent in cropping system A2, where spring wheat had been grown in 1984. The highest counts of yellow rust were recorded in crop- ping systems A 3 and B, but the deviation be- tween individual plots was considerable. Brown rust infected, on the average, 10 % of plants in all cropping systems (Fig. 2). Foot rots, caused mainly by F. avenaceum and F. culmorum, were more frequent in con- ventional than in organic cropping systems (30 % and 23 % respectively, % 2 = 17.93***). Significant variation in the occurrence of foot rots between years (x 2 = 347.69***) as well as between replicates (x 2 = 16.41***) was ob- vious. Average root rot severity was much higher in 1983 than in 1986 (23 and 8, respectively, F = 889.59***). Cropping systems had no statistically significant effect on root rot severity (F = 0.05). The most common patho- gens isolated from roots were F. avenaceum, F. culmorum and G. graminis. Also B. soro- kiniana and Rhizoctonia- species were found occasionally. In 1983, G. graminis was ex- tremely frequent on roots in organic plant pro- duction (Cl and Cl), while the counts were lowest in organic cattle production (D 1 and Table 4. Root rot severity and occurrence of Fusarium spp. and Gaeumannomycesgraminis on roots of winter wheat in 1983 and 1986 in conventional and organic cropping systems at growth stage 95. Group of cropping Root rot severity Fusarium % G. graminis % SyStCmS 1983 1986 1983 1986 1983 19X6 Conventional plant production 20»* 8» 43» 26» 53' 18» cattle farm 19» 7' 33» 22» 27 b 25» Organic plant production 26» 8' 17»h 22» 100» 18» cattle farm 25» 8» 3" 18» 7" 22» * Means with the same letter within one year do not differ statistically (p = 0.005). 344 Fig. 2. Occurrence of powdery mildew (in 1983), leaf blotch and yellow rust (in 1986) on three upper leaves of winter wheat in conventional and or- ganic cropping systems. Bars with the same letter do not dif- fer statistically (p = 0.005). D2). Fusarium species were more frequent in conventional than in organic cropping systems (F = 33.11***). In 1986, there were no statisti- cally significant differences in the occurrence of root rot pathogens between individual or any groups of cropping systems (Table 4). Discussion Seed-borne diseases were of minor impor- tance during the experiment even in organic cropping systems where no chemical seed dressing was made. This is probably due to the high quality of commercial seed used throughout the experiment. Poor germination and severe pathogenic contamination of seed harvested in organic cropping systems indicate increasing risk of seed-borne diseases on ac- tual organic farms where domestic seed is used year after year. The occurrence of foliar diseases is highly dependent on weather during the growing sea- son. Disease incidence was too low to make any comparisons between cropping systems in the relatively dry summers of 1982, 1985 and 1988 (Hannukkala et al. 1990), when barley was grown in all of them. The foliar diseases attacked winter wheat more seriously in con- ventional than in organic cropping. In 1983, the control threshold of powdery mildew was exceeded (Kurtto 1986). The crop was, how- ever, not sprayed, because no fungicide was registered for that purpose in Finland. More severe epidemic of powdery mildew in conven- tional than organic farming has been reported by El Tin and Landes (1988). In their study, higher Septoria-blotch infestation was re- corded in organic than in conventional farm- ing. Susceptibility of plants to foliar diseases is known to increase with an increasing rate of nitrogen application (Huber and Watson 1974). The lower incidence of powdery mil- dew in organic cropping can also be explained by the beneficial effect of slow-acting nitro- gen fertilisers (El Tin 1986). The occurrence of soil-borne foot and root rot diseases and pathogens was of roughly the same level as that reported by Mäkelä and Parikka (1980) in conventional farms in Southern Finland. During the first two years of the experiment, when the crop sequences were principally the same in all cropping sys- tems, the heavier foot and root rot infestation occurring in organic cropping systems was probably caused by the low nutrient level and type of manures applied. Towards the end of the experiment, the differences between crop- ping systems decreased, which indicates that the effects of diverse crop sequences compen- sated for the effects of nutrient deficiency in organic cropping. Nutrient deficiency has been reported to in- crease G. graminis and B. sorokiniana (Huber 1981). Severe injuries caused by G. graminis have been reported after green manuring crops, such as subterranean clover (Butler 1959). Extremely high counts of the pathogen were also recorded in this study on winter wheat in organic cropping in 1983, when the preceding crop was barley under- sown with subterranean clover, while counts were low in organic cropping where slurry was applied. However, the effects of organic nitro- gen on the survival of G. graminis are very complicated (Huber 1981). The high infesta- tion of B. sorokiniana in organic cropping sys- tems can partly be explained by the use of bar- ley straw as the raw material for the organic manure applied. The status of fungal contami- nation of the straw was not analysed. The results of the experiment indicate that the main problem in organic cropping is how to ensure an adequate nutrient supply. As no chemicals are used for seed dressing, it is cru- cial to pay special attention to the quality of seed. Also the organic amendments may in- crease disease incidence, a fact which empha- sises the importance both of hygiene and of the origin of the raw materials used for or- ganic manures. Acknowledgement. We wish to thank Mr Pentti Heinä- nen, Mrs Pirkko Korhonen and Mrs Tuula Laine for tech- nical assistance during the study. 345 References Butler, F.C. 1959. Saprophytic behavior of some cereal root rot fungi IV. Saprophytic survival in soils of high and low fertility. Ann. Appi. Biol. 47: 28—36. El Tm, A. 1986. Management of cereal pests and dis- eases in integrated farming systems. Brit. Crop Pro- tect. Conf. Pest Dis. 1986: 147—155. & Landes, H. 1988. The integrated farming system of Lautenbach: a practical contribution towards sus- tainable agriculture in Europe. Proc. Conf. Sustain- able Agric. Ohio. 23—27.9.1988. Garrett, S.D. 1970. Pathogenic root-infecting fungi. 294 p. Cambridge Univ. Press, London. Huber, D.M. 1981. The role of nutrients and chemicals. P, 317—352 in Asher, M.J.C. and Shipton, P.J. (eds.): Biology and control of take-all. Academic Press. London, New York, Toronto, Sydney, San Francisco. & Watson, R.D. 1974. Nitrogen form and plant dis- ease. Ann. Rev. Phytopath. 12: 139—165. James, C.W. 1971. An illustrated series of assessment keys for plant diseases, their preparation and usage. Can. PI. Dis. Surv. 51: 39—65. Jensen, H.P. & Jorgensen, J.H, 1973. Reactions of five cereal species on the take-all fungus (Gaeuman- nomyces graminis) in the field. Phytopathol. Z. 78: 193—203. Juhnke, M.E., Mathre, D.E. & Sands, D.C. 1984. A selective medium for Gaeumannomycesgraminis var. tritici. PI. Dis. 68: 233—236. Hannukkala, A.0., Korva, J. & Tapio, E. 1990. The cropping systems at Suitia: The experimental design. 3. Agric. Soc. Finl. 62: 295—307. Kurtto, J. 1986. Milloin viljojen lehtilaikkujen torjun- ta kannattaa. Koetoim. ja Käyt. 43: 37. Lampkin, N. 1986. Fallbeispiele zum Öko-Landbau. Stu- dien tiber biologische Landbausysteme in Westeuro- pa und Nordamerika eine Literaturiibersicht zu Fragen der Ökonomie, Qualität, Ökologie, Vermark- tung und Energiebilanz. P. 237—269 in Vogtman, H., Boehncke, E. & Fricke, I. (eds.): Öko-Landbau eine weltweite Notwendigkeit. Linderman, R.G. 1989. Organic amendments and soil- borne diseases. Can. J. PI. Path. 11: 180—183. Marland, A. 1989. An overview of organic farming in the UK. Outlook Agric. 18: 24—27. Mäkelä, K. & Parikka, P, 1980. Root and foot rot dis- eases of cereals in Southern Finland 1975—1978. Ann. Agric. Fenn. 19: 223—253. Reis, E.M. 1983. Selective medium for isolating Coch- liobolus sativus from soil. PI. Dis. 67: 68—70. Stetter, S. & Leroul, N. 1979. Ensidig bygdyrkning. 11. Indflydelsen pä roddernes svampeflora. Tidsskr. Pl.avl. 83; 50—72. Tempe, J. de 1963. The blotter method for seed health testing. Proc. Intern. Seed. Test. Ass. 28, 1: 133—151. Tiittanen, K. & Blomqvist, H. 1983. Torjunta-aineiden myynti Suomessa 1982. (Sales of pesticides in Finland in 1982, summary). Kemia—Kemi 10(9): 759—762. Vanhanen, R. 1981. Experiments with non-mercury seed dressings on spring cereals. Ann. Agric. Fenn. 20: 89—91. Zadoks, J.C., Chang, T.T. & Konzak, C.F. 1974. A dec- imal code for the growth stages of cereals. Weed Res. 14: 415—421. Ms received September 14, 1990 346 SELOSTUS Suitian viljelyjärjestelmät V: Viljojen taudit Asko Hannukkala 1 ja Eeva Tapio2 1 Kasvinsuojelun tutkimuslaitos, Maatalouden tutkimuskeskus, 31600 Jokioinen 2 Kasvipatologian laitos, Helsingin yliopisto, 00710 Helsinki Suitian koetilalla järjestetyssä kenttäkokeessa vertailtiin vuosina 1982—1988 neljää tavanomaista ja neljää luon- nonmukaista viljelyjärjestelmää. Kasvitautien esiintymistä eri viljelyjärjestelmissä selvitettiin ohralla vuosina 1982, 1985 ja 1988 sekä syysvehnällä vuosina 1983 ja 1986. Kas- vustot tarkastettiin kahden viikon välein ja mikäli yli 1 % kasveista oli sairastunut, kerättiin kaikista koeruuduista 100 kasviyksilön otos, josta arvioitiin tautien peittämä ala kolmesta ylimmästä lehdestä. Tyvi- ja juuristotautien run- saus selvitettiin kasvuasteella 75 ja 95 keräämällä 50—200 kasvin otos. Kasveista arvioitiin silmävaraisesti tyvien ja juuristonkunto jamääriteltiin taudinaiheuttajalajistola- boratorioviljelmien perusteella. Siemensadosta tehtiin idä- tyskokeet ja määritettiin siemenissä esiintyvä taudinaiheut- tajalajisto. Siemenlevintäisiä tauteja, lentonokea ja ohranviirutau- tia todettiin kasvustoissa hyvin vähän. Peittauksesta luo- puminen luonnonmukaisissa viljelyjärjestelmissä ei joh- tanut siemenlevintäisten tautien lisääntymiseen, sillä ko- keen kylvösiemenenä käytettiin vuosittain hyvälaatuista kauppasiementä. Siemensadosta tehdyissä idätyksissä luonnonmukaisesti viljeltyjen siementen itävyys oli sel- västi heikompi kuin tavanomaisesti viljeltyjen. Lisäksi luonnonmukaisesti viljellyissä siemenissä esiintyi hyvin runsaasti ohrantyvi- ja lehtilaikkutautia (Bipohris soro- kiniana). Ohrasäästyi lehtiä vioittavien tautien tuhoilta niinä vuo- sina, jolloin ohraa viljeltiin sekä tavanomaisissa että luon- nonmukaisissa viljelyjärjestelmissä. Yksittäisissä kasveissa todettiin verkkolaikkua (Pyrenophora teres) ja rengaslaik- kua (Rhynchosporium secalis) kaikissa viljelyjärjestelmis- sä. Tavanomaisesti viljellyssä syysvehnässä esiintyi run- saasti härmää (Erysiphe grominis) vuonna 1983. Luon- nonmukaisesti viljellyssä vehnässä härmää todettiin erit- täin vähän. Vuonna 1986 syysvehnäkasvustoissaesiintyi yleisesti ruskolaikkua (Septoria nodorum) jakeltaruos- tetta (Puccinia striiformis). Tautien esiintymisessä oli erit- täin suuria koeruutujen välisiä vaihteluita, mutta keski- määrin ruskolaikkua ja keltaruostetta todettiin enemmän tavanomaisesti viljellyssä kuin luonnonmukaisesti viljel- lyssä vehnässä. Ruskolaikku oli erityisen yleinen tavan- omaisessa viljavaltaisessa viljelyssä, jossa vehnää oli edel- lisen kerran viljelty vuonna 1984. Tyvi- ja juuristotauteja esiintyi runsaasti sekä ohralla että syysvehnällä. Tutkimuksen alkuvuosina tyvi- ja juu- ristotauteja esiintyi enemmän luonnonmukaisissa kuin ta- vanomaisissa viljelyjärjestelmissä. Viljelyjärjestelmien vä- liset erot näyttivät tasoittuvan kokeen jatkuessa. Vuon- na 1988 tavanomaisesti viljellyssä ohrassa esiintyi enem- män tyvitauteja ja kasvien juuret olivat huonokuntoisem- pia kuin luonnonmukaisesti viljellyssä ohrassa. Yleisim- mät tyvitaudinaiheuttajat olivat syysvehnällä Fusarium avenaceum ja F. culmorum. Ohralla esiintyi lisäksi hy- vin runsaasti ohrantyvi- ja lehtilaikkua. Kasvien juuris- toa vioittivat samat taudinaiheuttajalajit kuin tyviä. Li- säksi ohran ja vehnän juurissa todettiin yleisesti musta- tyvitaudin aiheuttajaa (Gaeumannomyces graminis). Ohrantyvi- ja lehtilaikkua esiintyi kaikkina tutkimus- vuosina selvästi enemmän luonnonmukaisissa kuin tavan- omaisissa viljelyjärjestelmissä. Erityisen runsaana tautia todettiin niissä luonnonmukaisissa järjestelmissä, joissa kompostoimatonta kasvimateriaalia käytettiin lannoittee- na. Mustatyvitautia esiintyi erityisen runsaasti vuonna 1983 syysvehnässä. Eniten tautia todettiin luonnonmu- kaisissa viljelyjärjestelmissä, joissa ennen syysvehnää vil- jeltiin ohraa aluskasvina maa-apila. Tutkimuksen perusteella kasvitautien aiheuttamia on- gelmia luonnonmukaisessa viljelyssä voidaan pitää mel- ko vähäisenä verrattuna vaikeuksiin, jotka liittyvät riit- tävän kasvinravitsemuksen järjestämiseen. Kylvösieme- nen peittaamatta jättäminenedellyttää, että kylvösieme- nen terveyteen kiinnitetään erityistä huomiota. Lannoit- teenakäytettävä eloperäinen aines voi toimia tehokkaa- na tautien tartuntalähteenä, joten materiaalin alkuperä ja terveys tulisi selvittää huolellisesti. 347