Sclerotinia stem rot (SSR) is an increasing threat to winter oilseed rape (OSR) in Germany and other European countries due to the growing area of OSR cultivation. A forecasting model was developed to provide decision support for the fungicide spray against SSR at flowering. Four weather variables-air temperature, relative humidity, rainfall, and sunshine duration-were used to calculate the microclimate in the plant canopy. From data reinvestigated in a climate chamber study, 7 to 11 degrees C and 80 to 86% relative humidity (RH) were established as minimum conditions for stem infection with ascospores and expressed as an index to discriminate infection hours (Inh). Disease incidence (DI) significantly correlated with Inh occurring post-growth stage (GS) 58 (late bud stage) (r(2) = 0.42, P /= Inh(i). Historical field data (1994 to 2004) were used to assess the impact of agronomic factors on SSR incidence. A 2-year crop rotation enhanced disease risk and, therefore, lowered the infection threshold in the model by a factor of 0.8, whereas in 4-year rotations, the threshold was elevated by a factor 1.3. Number of plants per square meter, nitrogen fertilization, and soil management did not have significant effects on DI. In an evaluation of SkleroPro with 76 historical (1994 to 2004) and 32 actual field experiments conducted in 2005, the percentage of economically correct decisions was 70 and 81%, respectively. Compared with the common practice of routine sprays, this corresponded to savings in fungicides of 39 and 81% and to increases in net return for the grower of 23 and 45 euro/ha, respectively. This study demonstrates that, particularly in areas with abundant inoculum, the level of SSR in OSR can be predicted from conditions of stem infection during late bud or flowering with sufficient accuracy, and does not require simulation of apothecial development and ascospore dispersal. SkleroPro is the first crop-loss-related forecasting model for a Sclerotinia disease, with the potential of being widely used in agricultural practice, accessible through the Internet. Its concept, components, and implementation may be useful in developing forecasting systems for Sclerotinia diseases in other crops or climates.

The impact of Verticillium longisporum on single plant and whole plot yield of oilseed rape (OSR) was studied in field experiments with natural infection or artificial soil infestation. Disease incidence (DI) and disease severity (DS) correlated with the amount of inoculum provided at four different levels by addition of infested rapeseed straw to the soil. DI and DS were higher in 2003, a year with higher average soil and air temperatures, than in 2004, at similar levels of added inoculum. Maximum DI and DS levels achieved with artificial soil infestation were 54.3% and 0.57 (rating scale from 0 to 2), respectively, which was insufficient to induce significant yield reduction in whole plots. In contrast, a significant decrease in yield was recorded on single naturally infected plants removed from the field at growth stage (GS) 83 to 85. Yield losses of single plants accounted for 20 to more than 80% at DS levels above 5 (scale 0 to 9). The systemic spread of V. longisporum was significantly delayed in plants in the field with substantial colonization of the shoots not occurring before maturity stages. However, fungal systemic spread into the shoots was faster in 2003, consistent with the visual disease assessment in the field. Conversely, the pathogen systemically spread after 28 days in plants (susceptible cultivar ÔFalconÕ) in the greenhouse. Root dip inoculation with conidia suspension induced earlier and more severe disease symptoms than microsclerotia added to the soil. In contrast to the field, intense stunting was recorded on inoculated plants in the greenhouse. The susceptible cultivar, ÔFalconÕ, showed higher DS, stronger reduction in root and shoot lengths and a faster fungal spread in the plant tissue than the moderate susceptible cultivar, ÔTalentÕ. Climatic conditions appear to be responsible for the strong delay in fungal invasion of plants in the field. This may prevent the plants from stunting and mitigate the overall yield effects of the disease. This study indicates a significant yield damage potential of V. longisporum in areas with DI above 60% and conditions accelerating the systemic pathogen spread in the plants.

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