This morning one of our staff members found cucurbit downy mildew (CDM) on cucurbits in Hillsborough County.
With recent rainy weather and rain events spread throughout the forecast, there is likely a high risk for CDM pathogen spreading to other parts of southern and central NH, and perhaps beyond. If infection occurs, expect symptoms to start to appear in 5 days.
CDM can infect over 60 different hosts, including cucurbits such as cucumber, cantaloupe, watermelon, squash, and pumpkin. Producers of these crops should have protectant fungicides for CDM prior to any future storms. These are listed in the New England Vegetable Management Guide - go to the crops tab and select the appropriate cucurbit crop(s). Chlorothalonil or copper products (organic options) are protectant fungicides that most growers probably already have on-hand. Once CDM occurs in your area it will be important to switch from protectant fungicides to fungicides with specific activity against CDM. These are also listed in the New England Vegetable Management Guide.
Any conventional grower who was not able to get a protectant spray down prior to last night’s rain, who has not sprayed within the past week and is feeling concerned because they did receive rain – Meg McGrath from Cornell suggests applying a locally systemic fungicide such as Curzate (cymoxanil) as soon as possible.
Excellent photos of CDM symptoms, and more information about this disease, can be found here: https://www.vegetables.cornell.edu/pest-management/disease-factsheets/downy-mildew-of-cucurbits/. If you suspect you have CDM infections, please take photos and send them to your local extension specialist, or UNH Plant Diagnostic Lab e-mail: unh.pdl@unh.edu, or submit samples to the UNH Plant Diagnostic lab for confirmation using this form. https://scholars.unh.edu/cgi/viewcontent.cgi?article=2506&context=exten…
