Sclerotinia

Sclerotinia appears as a white fungus on carrots.

Scientists at the University of Wisconsin have obtained data on the interaction of Sclerotinia and various cultural practices. Following is a summary of background information and data they collected in recent years from several studies.

Soybean varieties differ in reaction to Sclerotinia stem rot. Cultivars range from moderately resistant to very susceptible within maturity groups 0 through IV. We were not sure if differences in cultivar reactions were due to plant architecture, relative maturity, or lodging characteristics. For example, early maturity cultivars were speculated to escape infection because of their usual short stature and early flowering. Late maturity cultivars were believed to be more diseased because of lush vegetative growth and later flowering. Wisconsin evaluated soybean cultivars for reaction to Sclerotinia stem rot in 1992. Cultivar performance in the presence of Sclerotinia stem rot is influenced by inoculum density, cultural practices, and climate. In most cases, yield was inversely related to the percent incidence of Sclerotinia stem rot, but there were exceptions. Specific cultivars may express a high incidence of Sclerotinia stem rot, but produced an above average yield. Cultivars differ in the ability of infected plants to set seed. Two cultivars with similar yield potential and disease incidence can differ in yield. There is evidence that some cultivars may compensate for diseased plants better than others.

Row Versus Drilled Soybeans

The crop canopy can greatly affect environmental conditions needed for infection and for subsequent disease development. Thus, cultural practices that modify the canopy environment have a potential impact on the incidence and severity of Sclerotinia stem rot. A major change in soybean production in the Upper Midwest in recent years has been a reduction of row widths from 30 inches (row) to 7-10 inches (drilled). Yields are often 20% greater for drilled soybeans than for 30-inch row widths. Wisconsin studies conducted in the mid 1980s showed the incidence of Sclerotinia stem rot to be greater in narrow row than wide row systems. Research over the past two years suggests that Sclerotinia stem rot is not always greater in drill soybean, especially in high disease potential environments (Table 1). Although yield is reduced by high incidence of disease in drilled systems, yield is still greater than in wide row systems. Drill planting systems should not be abandoned because of high Sclerotinia stem rot. Drill systems offer the highest yield potential regardless of disease incidence; and Sclerotinia stem rot may not develop every year.

Summary

Many agronomic practices can be modified to reduce the risk of yield loss due to Sclerotinia stem rot. Production practices designed for high yield potential should not be abandoned because of Sclerotinia stem rot. For example, early planting dates, drill plant systems, high plant populations, and high soil fertility increase yield potentials, but also promote the development of Sclerotinia stem rot. However, the soybean can compensate for lost plants, even at later stages of development, by producing more pods or larger seeds. Soybean cultivar selection is the foundation of a management system to control Sclerotinia stem rot. The development of resistant cultivars is currently a critical need.

Since there is no cure the carrots should be burned and the media should be disinfected.