Preparing for Watermelon Diseases and Melcast Fungicide Scheduling for Watermelon

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu; Mason Newark, University of Maryland; mnewark@umd.edu

Gummy stem blight (caused by Didymella bryoniae) is the most important foliar disease of watermelon in Maryland and Delaware. The disease affects leaves, stems and vines of watermelon (Fig. 1). Anthracnose (Fig. 2), which is caused by Colletotrichum orbiculare, also occurs yearly. In MD and DE, yield losses due to gummy stem blight and anthracnose of 20 to 100% would occur in the absence of effective fungicidal control.

Melcast is a weather-based spray advisory program for watermelon developed at Purdue University. Melcast was originally validated with Quadris (before widespread resistance occurred), and with chlorothalonil. We are currently validating Melcast again with Folicur and Inspire Super (Table 1). In 2012 downy mildew occurred in our region earlyand may have contributed to less than optimal performance of Melcast. We are testing these materials and schedules again in 2013.

To use Melcast on your farm, please call Karen Adams at (302) 856-7303 and give us your name and Fax number or e-mail address. More details about how the program works are available at our Disease Forecasting Web page, which is at a new location this year:
http://extension.umd.edu/mdvegetables/vegetable-plant-diseases

Figure 1. Gummy stem blight on the petioles (A) and leaves (B) of watermelon.

Figure 2. Anthracnose lesions on cucurbits are angular in appearance. Tiny black spots can be seen through a hand lens in the tan centers of lesions.