Cucurbit downy mildew (CDM) symptoms were identified and the CDM pathogen was isolated from cucumber plants in Cheshire County (southwestern NH) this afternoon, Friday July 7, 2023. There are few other reports in the region (https://cdm.ipmpipe.org/), and the forecasts you may be used to seeing have been suspended due to lack of funding.
With recent rainy weather and rain events spread throughout the forecast, there is likely a high risk for CDM pathogen spread throughout southern and central NH - and perhaps beyond. If infection results, expect symptoms to start to appear in 5 days.
Only cucumber and cantaloupe crops are at risk now. 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. Since we know that CDM is in the area, it may be worth switching 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 and who hasn’t sprayed within 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).
Monitor your crops, and keep an eye out for symptoms of CDM. Excellent photos of 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 to unh.pdl@unh.edu, or submit samples to the UNH Plant Diagnostic lab for confirmation.
The Extension Fruit & Vegetable team.
