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Causal organism - Septoria tritici (Mycosphaerella graminicola)
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There are no practical cultural control measures for S.tritici although date of drilling has a marked effect on disease establishment. Early drilled crops are exposed to incoming ascospores for longer periods and hence tend to have higher levels disease through the winter and early spring period. Later drilled crops may carry lower levels of disease through the winter period but this has little effect on the final level of disease in the crop as inoculum is rarely limiting, the final level of disease being determined largely by weather conditions during stem extension.
Control of S.tritici is based on preventing the disease becoming established on the upper three leaves of the wheat canopy. This entails beginning spray programmes as the final leaf 3 begins to emerge during April or early May (usually GS31-32). This early treatment protects leaves 3 and 4 from severe infection, thus ensuring that inoculum does not become established in the middle of the crop canopy. If inoculum does establish on leaves 3 and 4 it can then spread directly by physical contact or by rainsplash to the upper two leaves. However, during heavy rainfall the disease can be splashed to the upper leaves from the base of the crop. Most triazole fungicides have good activity against S.tritici and, because of their eradicant activity , can be applied up to 10-14 days after infection has occurred. Chlorothalonil is highly effective when applied in mixture with triazole fungicides. Due to resistance development strobilurin products are no longer effective against the disease, although they can still give yield responses when applied in mixture with triazole fungicides.
