Anthracnose and Gummy Stem Blight Are Reduced on Watermelon Grown on a No-Till Hairy Vetch Cover Crop.

Multiple applications of fungicides are used to manage anthracnose caused by Colletotrichum orbiculare and gummy stem blight caused by Didymella bryoniae, the two most common and destructive diseases on watermelon (Citrullus lanatus) in the mid-Atlantic region of the United States. To develop a sustainable, nonchemical management option, a split-plot experiment was conducted over 3 years to evaluate the effects of a no-till hairy vetch (Vicia villosa) cover crop on disease severity, plant growth, and fruit yield compared with two conventional bedding systems and fungicide application. The main plots were bedding strategies consisting of bare ground, polyethylene covering, or a hairy vetch cover crop that was planted in the fall, killed the following spring, and left on the soil surface as an organic mulch. The subplots were a nonfungicide control or a weekly application of a standard fungicide program. Hairy vetch mulch provided greater than a 65% reduction in the area under the disease progress curves of anthracnose and gummy stem blight and greater than an 88% decrease in diseased fruit compared with bare ground or polyethylene mulch. The reductions were comparable with those achieved by fungicide applications. Watermelon vine lengths in plots with hairy vetch were similar to or greater than those in plots with polyethylene or bare ground that were treated with fungicides. Marketable fruit in plots with hairy vetch was higher compared with bare ground in 2 of 3 years and was similar to that in plots treated with fungicides in all 3 years. Addition of fungicide application to hairy vetch treatment further reduced anthracnose in 1 year and gummy stem blight in 2 years but did not significantly increase fruit yield in all 3 years. This is the first demonstration that a no-till hairy vetch production system can reduce anthracnose and gummy stem blight on watermelon and that the production system has the potential to mitigate damage caused by these diseases.