Cucurbit Downy Mildew Now Present in the Region

Jake Jones, Extension Agriculture Agent, Kent County;

Downy mildew was found on processing cucumber in Hurlock, Maryland on Monday, July 6, 2020 and Milford, Delaware on Tuesday, July 7, 2020. Widespread rain throughout the region on Friday, July 10, 2020 will accelerate the oncoming epidemic by providing near optimal conditions for infection, cool temperatures and prolonged periods of leaf wetness. All cucumbers are now at risk in the region and should receive preventative fungicides sprays with downy mildew specific fungicides. Research from UD and UMD has shown the importance of fungicide timing, with significantly less downy mildew severity in earlier applied treatments on both resistant and susceptible cucumber varieties. Effective fungicides are listed in the Mid-Atlantic Commercial Vegetable Production Recommendations: cooperative-extension/sustainable-production/commercial-crops/vegetable-crops/midatlantic-vegetable-recommendations/. Fungicide bioassays from UMD have shown Orondis, Zing!, Bravo, Ranman, and Omega to be some of the most efficacious fungicides tested on cucumber seedlings (2016-2019). Fungicide rotation, tank-mixing with a protectant fungicide, and the use of resistant varieties can help maintain the efficacy of fungicides and reduce cucurbit downy mildew severity.

Currently, downy mildew has only been found in cucumber and the strain that infects other cucurbit vegetables has not been observed in our region but can be expected later in the summer.