Please be aware that Cucurbit Downy Mildew (CDM) has been identified in the Mid- Hudson Valley, specifically Dutchess County. This is a fast moving and very destructive disease as windblown spores from this infection site are a primary source of infection for other cucurbit plantings in the area. Spores are easily dispersed long distances.
All cucurbit types may be affected, with cucumbers being the most sensitive followed by melons. According to the CDM forecasting program, southern NY was included in the areas with a “high risk” of spore deposition and infection back on July 7th , 11th and 13th, so with the weather conditions we’ve had symptom development is pretty much on target (7-10 days). CDM Forecasting model can be accessed at: http://cdm.ipmpipe.org/ .
If you are in the Hudson Valley or another high risk area, now is the time to apply mobile (systemic, translaminar) fungicides with an active ingredient that specifically targets DM. For conventional growers I have seen where a tank mix of Curzate plus Ranman or Zampro plus a protectant like chlorothalonil (Bravo, Initiate etc.) has done a very good job. Curzate provides some kickback or burnout activity but does not have much residual which is why it needs to be tank mixed with a second mobile fungicide or another application needs to be made 3-4 days later. Mobile fungicides are needed to control the disease from developing on the UNDERSIDE of the leaf. Fungicides should be re-applied according to disease severity and label instructions (keep pre harvest intervals in mind, maximum use rates and please rotate chemical classes using the FRAC codes found on all the labels. More information including risks forecasts and fungicide recommendations can also be found in the CCE ENYCHP Weekly Vegetable Updates
According to Cornell Pathologists Margaret McGrath, one of the better organic products evaluated is Timorex Gold (Tea Tree oil) and is labeled in NYS (click the name to see a copy of the label). See label for the rates and note that there is a 48-hour re-entry interval and do not apply within 48 hours of harvesting. Do not spray during the warm hours of the day and in hot seasons with temperatures above 95ºF (35ºC) and Do not apply this product through any type of irrigation system. Alternate with copper every 5-7 days.
If you suspect CDM please contact your local CCE ENYCHP educator for confirmation and help in establishing a treatment plan.
More information can be found on Cornell Pathologists Margaret McGrath’s bulletin on “Effectively Managing Cucurbit Downy Mildew in NY in 2017″ for details. http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Cucurbit%20Downy%20Mildew%20MGT-NY-2017-McGrath.pdf
Growers looking for information on OMRI/ organic approved products for downy mildew please see: “Biopesticides for Managing Cucurbit Crop Diseases Organically” also complied by Margaret McGrath.
Also see, “Efficacy of Organic Fungicides for Vegetable Diseases.” Found at: