A Crop Loss-Related Forecasting Model for Sclerotinia Stem Rot in Winter Oilseed Rape

Abstract

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 </= 0.001). Using the sum of Inh from continuous infection periods exceeding 23 h significantly improved correlation with DI (r(2) = 0.82; P </= 0.001). A parallel GS model calculates the developmental stages of OSR based on temperature in the canopy and starts the model calculation at GS 58. The novel forecasting system, SkleroPro, consists of a two-tiered approach, the first providing a regional assessment of the disease risk, which is assumed when 23 Inh have accumulated after the crop has passed GS 58. The second tier provides a field-site-specific, economy-based recommendation. Based on costs of spray, expected yield, and price of rapeseed, the number of Inh corresponding to DI at the economic damage threshold (Inh(i)) is calculated. A decision to spray is proposed when Inh >/= 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.

Susceptibility of winter rape cultivars to fungal diseases and their response to fungicide application

“…Seed losses from phoma stem canker usually reach 10%, but in some years they can reach 30%-50% (Hall et al, 1993;Zhou et al, 1999). Alternaria black spot (Alternaria brassicae) and sclerotinia stem rot (Sclerotinia sclerotiorum) are also very important fungal diseases of oilseed rape (Hong et al, 1996;Koch et al, 2007).…”

Sclerotinia sclerotiorum disease prediction: A review and potential applications in South Africa

“…28 Approximately 48-72 hours of continuous leaf wetness, RH ≥85% and temperatures of 20-25 °C are required for infection by ascospores. 5,18 However, infection by ascospores and subsequent disease development have been recorded at RH as low as 25% and soil moisture of 30%. 2,29 Mycelium is more tolerant to desiccation than ascospores and thus is more tolerant at lower RH.…”

“…2 Yield losses caused by S. sclerotiorum, particularly on canola in Sweden, the United Kingdom and Germany, may reach between 50% and 70%. 4,5 Canola is the third most valuable crop in Canada, where production has been severely affected by S. sclerotiorum. 6 In sunflowers, Sclerotinia head rot has been responsible for USD200 million damage annually in America.…”

Advances of Fungicide Application for Winter Oilseed Rape

“…Sclerotinia stem rot has been reported as one of the most harmful diseases in many countries (United Kingdom, France, Germany, etc.). Different opinions exist regarding economic importance of the disease, as, in some cases, yield losses of up to 50% have been reported (Koch et al, 2007). However, there are data that at least half of fungicide applications have been unnecessary (Young et al, 2007).…”