White mold, also known as sclerotinia stem rot, has spread in recent years, partly due to cultural practices that accelerate soybean canopy development and increase yield potential. The disease develops in humid conditions beneath the soybean canopy in seasons with wet weather conditions and moderate temperatures during flowering.
Application of Cobra® herbicide has been shown to reduce white mold incidence and increase yield of susceptible soybean varieties in some studies (Oplinger et al., 1999). However, yield results have been highly variable overall (Nelson et al., 2002). In fact, studies have shown yield losses in the absence of the disease, and researchers have therefore advised caution when considering use of this product for white mold control (Dann et al., 1999).
Cobra Effects on Soybeans - Cobra is a herbicide for postemergence weed control in soybeans. Herbicides with PPO-inhibiting sites of action such as Cobra usually cause moderate levels of leaf necrosis. The reduction in leaf area from this necrosis reduces or "opens" the soybean canopy and may be a contributing factor in white mold suppression with Cobra. On the other hand, yield losses may result in the absence of the disease.
White Mold Management - Few chemical solutions have been available for white mold management, which may lead some growers to consider application of Cobra to their soybeans for this purpose. However, the downside risk may be significant. For this reason, Pioneer researchers conducted extensive studies to clarify the possible yield effects due to Cobra application in seasons when white mold is not an issue for growers and in the absence of weed pressure.
¹by Don Kyle, Pioneer Research Scientist, Princeton, Ill. The author gratefully acknowledges Landon Ries, Pioneer Research Scientist, for statistical support; and Eric Egan, Pioneer Research Associate, for assistance in conducting this study.
Soybean variety responses to herbicides are variable and subject to many different environmental stresses, including temperature, moisture and other factors. Individual results may vary.
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