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Section 18 Specific Exemption Approved for Quintec to Manage Cucurbit Powdery Mildew in NY in 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

Registration of Procure in NY provides growers with valuable tool to manage cucurbit powdery mildew

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

Section 18 Specific Exemption Approved for Quintec to Manage Cucurbit Powdery Mildew in NY in 2006

Quintec 2.08SC (EPA Reg. No. 62719-GTL) can be used in NY for cucurbit powdery mildew following granting of a specific exemption by EPA to NYS DEC.  This use was requested because powdery mildew cannot be controlled effectively on the lower surface of leaves with currently registered fungicides due to resistance to QoI and DMI fungicides and usage constraints on the label and in the FRAC resistance management guidelines.  This exemption includes all counties in New York State. Quinoxyfen, the active ingredient in Quintec, has a new mode of action not in any registered fungicides.  It is in FRAC Group 13.  Cross resistance has not been detected with other fungicides.  Although it is not systemic, it moves into leaf surfaces and redistributes, and it has a vapor phase.  Excellent control achieved on the underside of leaves is thought to be due to redistribution via its vapor phase.  Quintec is currently registered by EPA on grapes, hops and cherry.  It is marketed by Dow AgroSciences LLC.

Quinone outside inhibitor (QoI) fungicides, a.k.a. strobilurin fungicides (FRAC Group 11) are no longer adequately effective because of resistance. The qualitative nature of this resistance (meaning pathogen isolates are either sensitive or highly resistant) and general cross resistance among QoIs means obtaining control with this group of fungicides where resistance occurs will be difficult.  Poor control was evident in commercial pumpkin fields monitored on Long Island in 2003.

Resistance to demethylation inhibitor (DMI) fungicides (FRAC Group 3) is also widespread.  This type of resistance is quantitative, meaning isolates of the pathogen exhibit a range in sensitivity to a DMI depending on the number of gene changes.  Pathogen isolates also exhibit varying response to different DMIs depending on their activity. In the USA, resistance to DMIs in the cucurbit powdery mildew pathogen is at the point that Bayleton is no longer effective while Nova is still effective at high rates despite reduced sensitivity. Nova applied at lowest label rate has been associated with poor control.  There continues to be concern that using Nova or Procure, another DMI, unwisely (not in alternation with other mobile fungicides in a good resistance management program) will eventually select for pathogen strains with greater resistance to this group of fungicides such that these are no longer effective.  Including Quintec in fungicide programs will facilitate effectively controlling powdery mildew and managing resistance to DMI fungicides. 

Quintec can be applied a maximum of 3 times at 4 fl. oz./A with a minimum of 10 days between applications as a foliar spray to melons, winter squash, gourds, and pumpkin (non-edible peel cucurbits) from July 1 through September 30. Consecutive applications are not permitted to minimize selection pressure for resistance.  Maximum allowed per acre is 12 fluid ounces.  Pre-harvest interval is 3 days.  To minimize risk to non-target organisms, label restrictions require applications be made between one-half hour after dawn and one-half hour before dusk, only when there is a wind away from fish-bearing waters, and where there is a well-maintained vegetative buffer between treatment area and fish-bearing waters. 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.

Quintec has provided excellent control of powdery mildew on lower surfaces of leaves as well as on upper leaf surfaces. In 2 recent fungicide evaluations conducted at Cornell in Riverhead, best control on the lower leaf surface was obtained with Quintec: 86% in 2003 and 98% in 2004.  Quintec was applied alone on a 7-day interval to determine its efficacy in these experiments, a use pattern that should never be used in a commercial field.  Similar level of control was achieved in 2004 using an alternation program with Procure plus the protectant sulfur applied each weekly.  The fungicide programs tested in 2003 were less effective than Quintec alone because they included a QoI fungicide rather than Quintec.

A recommended fungicide program (7 to 10 day interval) for 2006 consists of Quintec plus a protectant fungicide (sulfur, chlorothalonil, copper, etc.) applied in a 3-way alternation with other mobile fungicides, a DMI fungicide (Procure or Nova at high label rate) and Pristine (FRAC Group 7 and 11), plus a protectant fungicide with each. Pristine contains another new fungicide, boscalid, as well as a QoI fungicide. The first application should be made either preventively or shortly after detecting powdery mildew at the action threshold of at least 1 of 50 old leaves with symptoms.  Quintec, like the DMIs, has a narrow spectrum of activity.  Therefore it is critical to monitor crops for diseases other than powdery mildew.

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