Control of gummy stem blight of watermelon with plant defense activators combined with fungicides

Donald L. Hopkins


Gummy stem blight, caused by Didymella bryoniae (Auersw.) Rehm, is the most destructive foliar disease of watermelon in the southeastern United States. During warm, rainy weather, gummy stem blight is difficult to control with fungicides. The plant defense activator, acibenzolar-S-methyl (ABM), controls disease by activating the plant's own disease resistance system. In this study, the potential role of ABM in the control of gummy stem blight of watermelon was investigated. ABM applied to watermelon seedlings reduced the development of primary crown lesions of gummy stem blight in the early season. These crown lesions serve as the source of inoculum during rainy weather that is favorable for plant defoliation by gummy stem blight. Season-long control of the disease was best when ABM applications were begun in the transplant house and continued throughout the season along with conventional fungicides. ABM alone did not provide adequate control of gummy stem blight. ABM in combination with fungicides, such as mancozeb, chlorothalonil, and the strobilurins, can be an important component in a disease management program for gummy stem blight of watermelon.


citrullus lanatus; didymella bryoniae; acibenzolar-s-methyl; strobilurins

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283