Evaluation of fungicidal control of sclerotinia stem rot (SSR) on rapeseed Yin Chen Description of the disease affecting crops Sclerotinia stem rot (SSR) is caused by the fungus called sclerotinia sclerotiorum (Lib.) de Bary. It is a common disease in rapeseed (Brassica napus) fields. In Sweden, S. sclerotiorum can cause a 60% yield reduction in infected fields (Nordin, 1992). SSR is a major disease of canola in North Dakota. Incidence ranged from 7 to 19% in North Dakota from 1991 to 1993 (Lamey, 1995). It occurs almost every year and in most regions of the state. Symptoms on rapeseed appear when blooms appear two to three weeks after infection. Softness is the first visible symptom. The petals are the first part to be infected, then the infection can spread to the leaf petioles and finally to the stems. Light brown discolored spots will appear on stems, branches and pods. These lesions will expand and the surface of the plant will turn grayish-white in color. When the main stem is infected, the canola plant will be easy to root. Hard, black structures called sclerotia (survival structure of the pathogen) will be produced on the infected tissues once the infection is well established. It can be found inside the infected stem. Pathogens, including disease cycles. The fungus sclerotinia sclerotiorum overwinters as sclerotia in the soil or stubble on the soil surface (Morton and Hall, 1989). If the weather (humidity and temperature) is favorable, small mushroom-like structures called apothecia will be produced on the sclerotia. Each sclerotium can contain several apothecia. Apothecia can produce millions of spores called ascospores. The ascospores will be released into the air when the apothecium is mature. Some ascospores settle on rapeseed plants and infect dead rapeseed tissue as fal... half of paper......nt. Furthermore, air treatment has no effect on disease control. DiscussionThis practice is not recommended. There are three reasons. First of all, the air treatment is not effective at all. There is no data to demonstrate whether air treatment can effectively remove senescent flowers from maturing plants, and it is unclear whether removal of senescent flowers has an unstable effect on disease control. Even though fungicides were applied, yield and plant weight did not increase, and disease incidence and severity were sometimes higher than in the untreated control on fungicide-treated plants. Additional information needed The recommended application rate of each fungicide and whether air treatment can truly remove senestici flowers effectively.Summary This management practice is not recommended as it is unlikely to control sclerotinia stem rot in fields rapeseed or improve yield.