Integrated Management of Gummy Stem Blight of Watermelon by Green Manure and Melcast-scheduled Fungicides

Abstract

Watermelon gummy stem blight (GSB) management using a green manure cover crop, the weather-based disease forecasting program ‘Melcast,’ and bio- and reduced-risk fungicides was evaluated in Maryland. Soil incorporation of hairy vetch winter cover crop suppressed percent foliage affected by GSB in comparison to winter fallow in three of five trials conducted in 2004 and 2005. Programs of Reynoutria sachalinensis, Bacillus subtilis, or harpin protein applied in rotation with chlorothalonil provided control of GSB as effectively as did EBDC, boscalid, or cyprodinil plus fludioxonil. However, the bio-fungicide programs did not perform as well as chlorothalonil alternated with pyraclostrobin plus boscalid in 2005. Melcast-scheduled sprays of B. subtilis in rotation with chlorothalonil resulted in an average of 73% less synthetic fungicide applied to watermelon. However, GSB reduction in the B. subtilis program, although similar in 2005, was less that that obtained with chlorothalonil alone in 2004. These results suggest that the combined use of green manure with Melcast-scheduled fungicide applications could effectively manage GSB and reduce fungicide use. Biofungicides alternated with chlorothalonil also minimized use of synthetic fungicides and were effective under some conditions, but should be used with caution. Accepted for publication 22 September 2008. Published 20 November 2008.