Open access publications in the SLU publication database

Abstract

The relationships between plant diseases, winter wheat characteristics, air temperature and precipitation, site factors and agricultural practices were investigated. Regression analyses revealed that control of LBDs (Leaf Blotch Diseases, including septoria tritici blotch, stagonospora nodorum blotch and tan spot) explained 74% of the yield increase achieved by fungicide treatment at GS 45-61, followed by powdery mildew (20%), brown rust (5%) and yellow rust (1%). Yield of both untreated and fungicide-treated plots increased from 6000 to 12000 kg/ha over the period 1983-2005. Single eyespot treatment improved mean yield by ~320 kg/ha/yr during the period 1977-2002, mainly due to occasional years with severe eyespot. A fungicide treatment at GS 45-61 increased mean yield by 10.3% or 810 kg/ha/yr (9.9% or 660 kg/ha/yr for 1983-1994 and 10.7% or 970 kg/ha/yr for 1995-2005) due to increased TGW and grain numbers, especially in high yielding stands. Air temperature and precipitation as monthly means explained more than 50% of the variation between years regarding yield increase, TGW, LBDs, brown rust, yellow rust and eyespot, but less than 50% of the variation in yield and powdery mildew. Precipitation in May was the factor most consistently related to LBD disease intensity, and adding another two weather factors further improved the degree of explanation. Weather factors in the preceding growing season influenced growth stage, powdery mildew and brown rust. Mild winters and springs favoured the biotrophs, i.e. powdery mildew, brown rust and yellow rust. The mean net return from fungicide use was negative in 10 years and less than 50% of the entries were profitable to treat in 11 years. Fungicide use was in fact more profitable (mean net return 21 compared with 3 €/ha) during the latter part of the period (1995-2007) than in the earlier part (1983-1994). The role of site factors and agricultural factors is complex but some factors, such as pre-crop and dose of nitrogen, can probably be used in plant disease warning and prediction models. Wheat as pre-crop to wheat gave 1.6 tons/ha lower yield than rape as pre-crop. The results confirm the potential and limits of fungicides and the need for supervised control strategies that include factors affecting disease, yield, interactions and overall profitability.