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New fungicides fight mildew: new products designed to combat powdery and downy mildew undergo multiple trials.

Disease management in vineyards, especially in the humid and often wet climates found in the East, requires that grapegrowers integrate both chemical and non-chemical approaches. This article, part two of two for Wine East, reviews some of the new fungicides now available to help growers control both powdery and downy mildew.

Among new fungicide products recently registered for use on grapes in the United States are three difenoconazole products. Difenoconazole (DFZ) is an important "new" (to the United States) sterol inhibitor/DMI fungicide packaged under three different trade names, depending on the "partner" fungicide with which it is mixed. These various DFZ-containing products have different attributes depending on the mixing partner employed--and in some cases significantly different per-acre costs. It also is important to pay attention to the amount of active ingredient of the different components in each one.

During the six trials where we've looked at it (two each during the past three seasons), DFZ has provided excellent to outstanding powdery mildew control, far superior to that provided by our traditional DMI materials (Rally/Nova, Vintage/Rubigan, Elite/tebuconazole generics). As many growers are aware, performance of the standard DMI products has been "slipping" in a number of locations during recent years, and during a 2010 Chardonnay trial that we ran, a seasonal program applying Rally at its maximum label rate of 5 ounces/acre provided zero control of the disease on clusters, and they were completely destroyed. In stark contrast, two different DFZ products (Revus Top, Inspire Super) provided almost complete control.

What was the reason? Lab studies proved what we first suspected: The dose of myclobutanil, the active ingredient in Rally required to provide a given level of control of the powdery mildew fungus, is many times greater than the dose of DFZ necessary to give the same control, yet their commercial products deliver comparable amounts of each in the field. No wonder the DFZ products work better.

DFZ also has given excellent control of black rot in trials conducted in other states. Labels claim control of a couple of additional minor/sporadic diseases including anthracnose, but I have no experience or knowledge related to these claims.

Three new fungicides

Revus Top: A mixture of DFZ and the new downy mildew-specific fungicide mandipropamid (the latter is sold alone as Revus), Revus Top is labeled at just one rate, 7 fluid ounces/acre. For the following discussion, it will be considered to provide the "full" rate of DFZ. In several of our trials, Revus Top (or the appropriate components used at the same rate) has given excellent control of both downy and powdery mildews under very high pressure. It also is very reasonably priced. This should be an attractive product for many growers, but it cannot be used on Concords and is risky for a few other natives and hybrids (see below).

Inspire Super: A combination of DFZ and cyprodinil (the active ingredient in the standard Botrytis fungicide, Vangard), Inspire Super is labeled at a use rate of 16 to 20 fluid ounces/acre. At the top 20-fluid ounce rate, it provides the same dose of DFZ as the labeled rate of Revus Top and the same dose of cyprodinil as 7 ounces of Vangard (the label rate for Vangard is 10 ounces/acre, or 5 to 10 ounces if mixed with another Botrytis fungicide; DFZ has no meaningful activity against Botrytis at the Inspire Super use rates).

Quadris Top: A combination of DFZ and azoxystrobin, the active ingredient in Abound, Quadris Top is labeled at a use rate of 10 to 14 fluid ounces/acre. At the top 14 fluid-ounce rate, it provides the same dose of DFZ as the labeled rate of Revus Top and the same dose of azoxystrobin as 11 fluid ounces/acre of Abound (the labeled use rate for Abound is 11 to 15.4 fluid ounces/acre).

Growers should be aware of resistance management considerations when using any of these products; e.g., remember that applying Inspire Super is the same thing as applying Vangard with respect to resistance management issues for the AP fungicides (Vangard, Scala), and that applying Quadris Top is the same thing as applying Abound with respect to strobie issues. And, of course, do not apply any combination of these or other DMI (Group 3)-containing fungicides more than three times per year,

As noted previously, DFZ can cause injury to Concords and a handful of other native cultivars and hybrids. The whole story is not yet clear, but field observations made by Cornell Cooperative Extension, Syngenta personnel and various consultants and nurserymen during the 2010 season identified the following varieties as having incurred some injury in the Finger Lakes and Lake Erie regions of New York: Brianna, Canadice, Concord, Concord Seedless, Frontenac (minor), Glenora, Noiret (minor), Skujinsh 675 [interspecific hybrid containing V. vinifera, V. amurensis, V. labrusca, and V. riparia], St. Croix (minor) and Thomcord (Thompson seedless x Concord ).

The following varietals showed no injury: all V. vinifera cultivars observed, Aurora, Backus, Baco Noir, Catawba, Cayuga White, Chambourcin, Chancellor, Chelois, Colobel, Corot Noir, deChaunac, Delaware, Diamond, Elvira, Foch, Fredonia, Interlaken, Leon Mil-lot, Niagara, Rougeon, Seyval Blanc, Steuben, Traminette, Vidal Blanc and Vignoles.

It also is worth noting that, in both follow-up experiments and anecdotal observations, injury was much more severe when the product was applied with a standard rate of a nonionic surfactant (NIS) than it was if no surfactant was used, and it was more severe yet when applied with the recommended rate of a surfactant that combined an NIS with an organosilicate material. These varying levels of injury correspond to the relative degree of promoted fungicide absorption that you would expect with these surfactants.

Another brand new product that received its first EPA registration in December is called Vivando. It is a powdery mildew-specific fungicide that has shown outstanding activity in our trials, giving 100% control last year on Chardonnay clusters subjected to extreme pressure (no sprays whatsoever before bloom, untreated and ineffectively treated vines throughout the plot, 14-day intervals).

CAUTION: Do not try this at home--if you try to burn out a material you'll probably succeed! However, these results do illustrate the strength of the product. Vivando represents a new class of chemistry, so there are no cross-resistance issues and it should be a useful addition to rotational programs. This could well become one of our "big guns," especially if it is priced competitively.

Downy mildew-specific fungicides

Downy mildew is Public Enemy No. 1 for several million acres of European vineyards, and growers in Europe may spray a dozen or more times per year to control it. Hence, it's a very attractive target for fungicide development, and many of the resulting products make it across the Atlantic Ocean to us. In addition to Revus/Revus Top, a few fungicides that have hit here recently include the following:

Forum (dimethomorph; Group 40 for resistance management purposes)--Same material as Acrobat, registered for many years on vegetable crops. Not much U.S. experience with it used as a solo product on grapes. It will be combined with a new active ingredient to form the new product, Zampro, whose registration is currently pending. Downy mildew activity only.

Presidio (fluopicolide, Group 43)--Unrelated to any other grape product on the market, it has had EPA registration for a couple of years but was just registered in New York. Presidio has locally systemic properties, hence some post-infection activity, although this is not well characterized. In our trials, it has consistently provided excellent control. Downy mildew activity only.

Ranman (cyazofamid, Group 21)--Also unrelated to any other grape product. Primarily a protectant fungicide, it has provided good to very good control in our trials when used alone, very good to excellent when tank-mixed with a phosphorous acid product to add post-infection activity. Downy mildew only.

Reason (fenamidone, Group 11)--Different from but same biochemical mode of action as the strobies, hence it is classified with them as a Group 11 material for resistance management purposes (i.e., you can't rotate among the same group, resistance to one is resistance to all). However, it also is different from existing strobie products in that it has a much narrower spectrum of activity (i.e., downy mildew only). Reason provided complete control of downy mildew in the one trial that we've run so far.


* This article, part two of two for Wine East, reviews some of the new fungicides now available to help growers.

* Performance of DMI products has been "slipping," but DFZ products provided almost complete powdery mildew control in trials.

* Several new European products for downy mildew are discussed.

Wayne F. Wilcox is a professor in the Department of Plant Pathology and Plant-Microbe Biology at Cornell University's New York State Agricultural Experiment Station at Geneva, N. Y. Craig N. Austin is a graduate student in the same department. Reach them through
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Title Annotation:WineEast
Comment:New fungicides fight mildew: new products designed to combat powdery and downy mildew undergo multiple trials.(WineEast)
Author:Wilcox, Wayne F.; Austin, Craig N.
Publication:Wines & Vines
Date:Apr 1, 2011
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