1. Occurrence, epidemic spreading of fungal diseases and their effect on crop yields of winter wheat depending on influence of year's weather and production methods as well as the development of systems for selective use of fungicides 1.4. Development and evaluation of growthstage specific disease-loss ratios of mildew (Erysiphe graminis DC f. sp. tritici Marchal) on winter wheat
1994
Heitefuss, R. (Goettingen Univ. (Germany). Inst. fuer Pflanzenpathologie und Pflanzenschutz) | Glattkowski, H. | Lassak, V. | Bodendoerfer, H.
In several years field experiments with different winter wheat cultivars and intensities of N-fertilization the mildew incidence (Erysiphe graminis) was continuously recorded and stopped by fungicide applications at different dates. The yield was determined and correlated to the average percentage mildew present at the upper three leaves at the start of fungicide protection. For the wheat growth stages EC 32 to EC 71 disease/loss-ratios were calculated. On their basis and a preliminary control threshold corresponding to 1.6 dt/ha yield loss, dates for necessary fungicide applications in 1990 were determined. From the data of three field experiments in 1987, 1988 and 1989, additional standard disease-respectively loss-functions were derived and utilized for prediction of the yield loss to be expected at a given mildew disease incidence. Comparing the predicted with the in fact measured yield loss shows partly a good, partly a not sufficient agreement. This is due to the systems immanent variability with the determination of small yield differences in field experiments. In spite of this however, the attempt appears promising to predict on the basis of growth stage specific disease/loss-ratios or functions the yield loss caused by mildew. Thereby it should be possible to develop control thresholds by means of which the applications of fungicides could be reduced to an economically justified level
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