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Registration of Procure in NY Provides Growers with Valuable Tool to Manage Cucurbit Powdery Mildew

June 2006

Margaret Tuttle McGrath

Department of Plant Pathology, Cornell University

Long Island Horticultural Research and Extension Center

3059 Sound Avenue, Riverhead, NY 11901; mtm3@cornell.edu

For current managment recommendations see Powdery Mildew Management Guidelines for 2010

See also:

Guidelines  for  Managing  Cucurbit  Powdery Mildew  in  2006

Section 18 specific exemption approved for Quintec to manage cucurbit powdery mildew in NY in 2006

Protectant fungicides for managing powdery mildew in cucurbits: how do they stack up?

Guidelines for managing cucurbit powdery mildew with fungicides in 2005

Occurrence of strobilurin resistance and impact on managing powdery mildew of cucurbits

For current managment recommendations see Powdery Mildew Management Guidelines for 2010

Registration of Procure in NY Provides Growers with Valuable Tool to Manage Cucurbit Powdery Mildew: June 2006

Procure is a valuable addition to the fungicide arsenal for combating powdery mildew in cucurbit crops because it is a DMI fungicide that can be applied at a high dose. It was registered in NY for this use in early 2006. DMI (demethylation inhibiting) fungicides (FRAC Group 3) are highly effective and they are mobile in leaves which enables them to suppress powdery mildew on the lower surface of leaves, where this disease develops best, resulting in excellent control.  DMIs have continued to be important for managing powdery mildew although resistance has developed in the pathogen.  This is because resistance to DMIs is quantitative and the current level of resistance in the pathogen is not sufficient to allow it to tolerate high DMI dose.  Thus Procure is highly effective despite resistance.  With quantitative resistance, pathogen strains exhibit a range in fungicide sensitivity depending on the number of genetic changes they possess that affect the fungicide’s ability to function. The first DMI registered for cucurbit powdery mildew, Bayleton, became completely ineffective due to resistance about 15 years ago.  Nova, the second DMI registered for this use, has continued to provide excellent control when applied at high label rates in fungicide efficacy experiments, but poor control has been reported with low label rates. DMIs are expected to continue to be important for managing cucurbit powdery mildew if resistance is managed.

Procure is labeled for use at up to twice the dose of Nova, the only other DMI registered for cucurbit powdery mildew.  Procure 50WS at the highest label rate of 8 oz/A provides 4 oz/A of its active ingredient (triflumizole), whereas Nova 40W at 5 oz/A provides 2 oz/A of its active ingredient (myclobutanil).  Although Procure was not more effective than Nova where compared recently in university fungicide efficacy experiments, including Cornell, and the highest label rate of Procure is not needed to effectively suppress powdery mildew, high rates are generally recommended for managing quantitative resistance.  High rates will control any pathogen strains present that are able to tolerate low doses.  When these moderately resistant strains are able to survive there is potential for development of strains with higher levels of resistance.  It is not possible to predict the genetic potential of the cucurbit powdery mildew fungus to continue developing DMI resistance, therefore high rates are needed.  Hopefully this pathogen is not capable of developing a sufficiently high level of DMI resistance that it will eventually be able to tolerate full label rates of Nova or Procure resulting in control failure as occurred with Bayleton.  It is important to realize that resistance needs to be managed before fungicide efficacy is affected, thus the recommendation to use high rates now.  Since managing further development of DMI resistance in the cucurbit powdery mildew pathogen is critical for successful disease control, Procure applied at a high label rate (6-8 oz/A) is thought to be a better choice than Nova at its highest label rate of 5 oz/A.  Cost is similar: about $17.63-$23.50/A for Procure versus about $21.53/A for Nova.  When compared in 2005 at Cornell in Riverhead, excellent control of powdery mildew was obtained on the lower leaf surface with both DMIs: 93% with Procure at 6 oz/A and 82% with Nova at 5 oz/A (these numbers are not statistically different).  To determine their efficacy in this experiment these products were applied alone on a 7-day interval, a use pattern that should never be used in a commercial field.

Note that the new 480SC formulation of Procure will soon replace the original 50WS formulation.  It is labeled for use at 4-8 fl oz/A, the same rate of active ingredient as the 50WS, with a season maximum of 40 fl oz/A.

In addition to applying Procure at a high label rate, other resistance management strategies need to be implemented for optimum resistance management and to ensure effective control of powdery mildew.  These strategies include selecting varieties with genetic resistance, applying Procure tank-mixed with a protectant (contact) fungicide, and applying Procure alternately with other mobile fungicides in different fungicide classes (FRAC groups).  Procure should not be alternated with Nova.  There are two other mobile fungicides to use in alternation with Procure in NY: Quintec and Pristine.  These also are at-risk for resistance development and thus are also recommended used in alternation.  Quintec (FRAC Group 13) was granted an emergency exemption (Section 18) by EPA to NYS DEC again for 2006 for powdery mildew in non-edible peel cucurbits.  Users must have a copy of this label when they use this product.  Quintec labels can be obtained from local distributors and the extension office as well as at http://pmep.cce.cornell.edu/regulation/sec18/2006/index.html.  Pristine (Group 7 and 11) is recommended over other Group 11 (QoI, aka strobilurin) fungicides (e.g. Amistar, Flint, Cabrio) because this is the only product in this fungicide group that has an additional active ingredient in another chemical class, boscalid (Group 7).  Cucurbit powdery mildew is the only vegetable disease that Procure and Quintec are labeled for.  Pristine is labeled for other diseases in cucurbits as well as other crops, but it was not as effective for powdery mildew.  Alternating among these 3 mobile fungicides, with each tank-mixed with a protectant, is expected to provide effective control of powdery mildew plus provide some control of some additional diseases.

Please Note: The specific directions on fungicide labels must be adhered to -- they supersede these recommendations, if there is a conflict.  Any reference to commercial products, trade or brand names is for information only; no endorsement is intended.

For current managment recommendations see Powdery Mildew Management Guidelines for 2010