Agroscope, Institute for Plant Production Sciences IPS, 1260 Nyon, Switzerland

Intervention thresholds for Septoria tritici

In the last ten years, Septoria tritici (ST) become one of the most important wheat diseases in Switzerland. To develop economic and intervention thresholds, 33 different situations from ten field trials with natural infections were analysed. Swiss wheat cultivars of different resistances were analysed from 1993 to 1997. For the economic threshold, a value of 10 % Septoria tritici- severity on leaf F-1 (F=flag) at dough development (GS 83-85) was found. From the economic threshold the intervention thresholds for the earlier growth stages 41-45 and 57-59 were derived. For both, a level of 15 % disease incidence (% of leaves with symptoms) on leaf F3 and F-2 respectively was obtained. Applying this threshold model, in 30 out of 33 cases an economically correct spray decision would have been taken.

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