Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2001
Publication Date: N/A
Interpretive Summary: Sclerotinia stem rot (SSR) of soybean is a major disease in the north central region of the United States with severe outbreaks in 1992, 1994 and 1996. Soybean flower petals are the primary site from which infection spreads to leaves, petioles and internodes. Adjacent plants can be infected through contact with diseased plant tissue. From 1995 to 2000, a multi-state effort collaborated to establish a series of laboratory, greenhouse and field experiments to study the effectiveness of fungicides for managing SSR infection and to evaluate application techniques in the field. In laboratory and greenhouse experiments, SSR infection was inhibited at different levels depending on the fungicide and the rate of application. Vinclozolin provided the most consistent protection. Benomyl and thiophanate methyl also prevented development of SSR system on leaf tissue on greenhouse grown seedlings. Ohio field tests showed that application technique could affect the amount of infection resulting from SSR. The air-assist treatment produced good protection as well as higher yields. These studies have shown that management plans for control of SSR would benefit from a strategy that could be implemented on an as needed basis during the growing season. Fungicides would offer this flexibility and would augment preventive measures put in place at planting. Application techniques, such as air-assisted delivery, should be selection based by growers on the ability to provide good canopy penetration and deposition on flower petals.
Technical Abstract: Sclerotinia stem rot (SSR) of soybean is a major disease in the north central region of the United States. One approach to inhibit growth of SSR on soybean is with the use of fungicides. Vinclozolin was the most effective of four fungicides in inhibiting S. sclerotiorum mycelial growth at 1.0 ug a.i./ml of PDA based on measurements of fungal radial growth on potato dextrose agar. Benomyl, thiophanate methyl and vinclozolin applied to greenhouse-grown seedlings prevented S. sclerotiorum from expressing symptoms or signs on leaf tissue. Of 13 different environments in Illinois, Ohio and Wisconsin from 1995 through 2000, six had no SSR pressure, three environments had low to moderate SSR pressure and four environments had high SSR pressure. When there was high disease pressure, no consistent control of SSR was observed with benomyl or thiophanate methyl using different application systems. However, under low SSR pressure, spray systems that were able to penetrate the canopy, reduced the incidence of SSR by 50%. Conventional fungicide applications made with flat fan and high- pressure, hollow cone nozzles and an air-assist sprayer, significantly reduced developed SSR incidence. Only the Ohio air-assist treatment resulted in significantly higher yields. These results have shown that fungicides can effectively inhibit SSR development, assuming sufficient spray coverage, particularly deeper in the canopy, can be achieved.