Phytophthora blight has proven to be a potentially devastating disease in cucurbit crops and a difficult disease to control. Successful management necessitates an integrated program that focuses on cultural practices for managing soil moisture. Fungicides can be a valuable component of a Phytophthora blight management program. It is important to realize that none of the fungicides and experimental materials tested to date in university efficacy studies have worked sufficiently well that they could be relied on as the primary management practice for this disease. For additional information on Phytophthora blight, its management and photographs see:

http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbit_Phytoph2.htm

http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Phytophthora2001.htm

http://www.apsnet.org/online/feature/cucurbit/

Gavel 75DF (EPA Reg. No. 62719-441) was registered in New York State in September 2003 for use on cucurbits as well as tomatoes and potatoes. It is labeled on cucurbits for downy mildew, Alternaria leaf spot, and fruit and stem rot. The registrant, Dow AgroSciences, did not list a specific fruit and stem rot disease anticipating that this fungicide would be effective for several pathogens causing fruit and stem rot. However, NYS DEC requires the target disease be listed on fungicide labels for the product to be applied for that use in New York. Phytophthora capsici was the target pathogen in Gavel efficacy experiments that have been conducted for fruit and stem rot. Therefore a FIFRA 2(ee) request was made for Phytophthora fruit and stem rot (aka Phytophthora blight) caused by Phytophthora capsici. This request has been approved. Applicators need a copy of the FIFRA 2(ee) Recommendation in their possession when Gavel is used for Phytophthora blight. A copy (tif file) can be obtained on the web at

http://pmep.cce.cornell.edu/pims/current/

Click on 'Product/Label Name' under 'Search for Products by'. Enter 'Gavel'. Click on 'details' in the right column. Click on 'NYS Labels/Docs'. Click on '69042', the label ID for the 2ee.

Gavel contains mancozeb (66.7%) and zoxamide (8.3%), a new active ingredient that specifically targets Oomycete fungi, a group which includes pathogens causing downy mildew and late blight in addition to Phytophthora blight. Gavel can be used on cucumber, melon, summer squash, watermelon but not on pumpkin because mancozeb is one of the ingredients. Mancozeb is formulated as Dithane Rainshield. When Gavel is used, workers must be notified that the area has been treated with a pesticide that is a dermal sensitizer by warning them orally. In addition, the label provides directions for posting warning signs when this product is used on cucurbits and tomatoes. It is classified as a restricted use product. Restricted-entry interval (REI) is 48 hours. Preharvest interval is 5 days.

Phosphorus acid, formulated as Phostrol (EPA Reg. No. 55146-83), is another fungicide recently labeled for Phytophthora blight that has been registered in New York. It is labeled for use in all cucurbits. Aliette WDG (EPA Reg. No. 264-516), containing the active ingredient aluminum tris, is also labeled for Phytophthora blight in all cucurbits. Acrobat is federally registered but NOT yet registered for use in New York.

Start applications of Gavel or other fungicides labeled for Phytophthora blight before symptoms have been observed and when cucurbit plants are young (two-leaf stage suggested), repeat at 7- to 10-day intervals or when conditions are favorable for disease for a maximum of 8 applications at 1.5 - 2.0 lb/A.

Very few university fungicide efficacy experiments that included Gavel and/or Phostrol for Phytophthora blight in a cucurbit crop have been published in Fungicide and Nematicide Tests. Most experiments with these new fungicides have been on late blight in potato. Gavel plus Kocide 2000 applied three times controlled Phytophthora fruit rot in cucumber as well as Acrobat plus Kocide 2000 in two experiments conducted in MI in 2002 (61 and 67% control versus 50 and 70% control, respectively). However, neither Acrobat plus Kocide 2000 nor Gavel applied in alternation with Dithane controlled Phytophthora fruit rot in cucumber in an experiment conducted in WI in 2002. Phostrol applied 7 times was among the most effective treatments evaluated on pumpkin in an experiment conducted in 2003 in IN which included several experimental materials (33% of fruit were infected versus 74% in non-treated plots). Neither Phostrol, Acrobat plus the copper fungicide Champion, nor the other fungicide treatments evaluated on summer squash in NY in 2003 were effective when applied 6 times on a weekly schedule at least partly due to very favorable conditions for Phytophthora blight (2 inches of rain fell on 4 days over a 7 day period). This range in results documents the challenges of effectively managing Phytophthora blight. Additionally, conditions are often more stringent in research fields due to presence of non-treated plants for comparison and poor rotation to ensure the pathogen is present.

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