Watermelon seedlings grown as transplants are susceptible to gummy stem blight, caused by
the fungus Didymella bryoniae, during greenhouse production. Cucurbits used as rootstocks to
graft watermelon—bottle gourd (Lagenaria) and hybrid squash (Cucurbita)—also are
susceptible. Gummy stem blight can be particularly serious on grafted watermelon seedlings.
After grafting, plants must be misted or held at high relative humidity for one week while the
vascular bundles of rootstocks and scions connect. These long, continuous periods of leaf
wetness are favorable for severe disease outbreaks. The objective of this project was to test
fungicides that control gummy stem blight in the field for efficacy on grafted watermelon
seedlings in the greenhouse.
