New grape fungicides for 2011
Four new materials are registered for use this year.
New products included in the powdery mildew toolbox for grapes include Adament (tebuconazole + trifloxystrobin), Inspire Super (difenoconazole + cyprodinil), Unicorn (tebuconazole + sulfur), and Vivando (metrafenone). Adament and Inspire Super, along with the existing products Flint (trifloxystrobin) and Pristine (pyraclostrobin + boscalid), provide the added benefit of also controlling Botrytis bunch rot, when applied at proper rates. Bunch rot was a problem in many eastern Washington vineyards last year. The full component of powdery mildew compounds is presented in the accompanying grape fungicide table.
The table includes fungicide class information, and Fungicide Resistance Action Committee group number, or code, a number representing the mode of action of the fungicide. This information is helpful when designing a fungicide program that conforms to FRAC resistance management guidelines. It is important to remember that if a pathogen population develops resistance to fungicides within a FRAC group, it is likely to be resistant to all members of that group. Resistance is more likely to develop if the pathogen is frequently treated with one or multiple fungicides within a given FRAC group.
Included in the table are members of the fungicide classes (or FRAC groups) known as benzophenones (metrafenone, Group U8), DMI (demethylation inhibitors, Group 3), QoI (quinone outside inhibitors; previously called strobilurins, Group 11), quinolines (quinoxyfen, Group 13), sulfur (Group M2), various “biological” fungicides (Group 44), petroleum-derived spray oils, and potassium bicarbonate. Petroleum spray oils and potassium bicarbonate are listed as “Not Classified” (NC) by FRAC. Several products are formulations or “premixes” of two different fungicide classes and modes of action or FRAC groups. Consult product labels for appropriate rates and spray intervals. The resistance risk is product-dependent. All of the aforementioned “new” products have performed well in efficacy trials at Washington State University's Irrigated Agriculture Research and Extension Center at Prosser.
New premix fungicides
The availability of “premix” or combination fungicide formulations is a relatively recent trend in agriculture. The grape toolbox contains several of these product types: Adament (tebuconazole + trifloxystrobin), Inspire Super (difenoconazole + cyprodinil), Pristine (pyraclostrobin + boscalid), and Unicorn (tebuconazole + sulfur). Both active ingredients in these compounds—with the exception of Inspire Super—have activity against powdery mildew (only the tebuconazole component of Inspire Super is active against the disease). When both modes of action have activity against the target organism, some level of resistance management is built into the products, provided that they are used rationally. The use of “premix” types of products can provide better disease control, provide disease control security if there is field resistance to one of the two active ingredients, and help prevent resistance if there is not.
A recent survey revealed that QoI (Group 11) or QoI-containing fungicide products (Abound, Flint, Pristine, and Sovran) were the industry’s first line of defense against powdery mildew. The resistance risk of these Group 11 fungicides (formerly known as strobilurins) is high, while the risk of other important classes (DMI, quinolones, and benzophenones) is considered medium. The resistance risk of contact fungicides sulfur, narrow-range petroleum oil, and potassium bicarbonate is low.
We have no evidence of fungicide-resistant mildew populations in eastern Washington, but this could change rapidly, given the nature of powdery mildew and the resistance history in grapes of Group 11 and Group 3 fungicides. Therefore, it is imperative that resistance management guidelines be followed beginning with the introduction of the group.
Resistant management guidelines
General resistance management guidelines include the incorporation of cultural practices that lower disease pressure. Cultural practices such as vigor management, shoot removal and positioning, and leaf removal help lower disease pressure and improve spray penetration. The incorporation of these practices serves to lower selection pressure on pathogen populations. Always use fungicides in a protective, rather than reactive, manner: It is far easier to prevent powdery mildew than to cure it.
Additional guidelines include:
- Limit the number of applications of individual modes of action per season, and limit sequential applications.
- Avoid tank-mixing or alternating fungicides with the same FRAC number in a spray program.
- Don’t apply medium-risk compounds such as DMI (Group 3) and quinoline compounds (Group 13) more than three times per season and no more than twice in sequence.
- Alternate high-risk QoI (FRAC Group 11) fungicides or premixed formulations containing them (Adament, Flint, Sovran, Pristine, and Abound) one-to-one with other modes of action or groups. It is preferable to make only one application of any resistance-prone compound, and then switch to a fungicide from a different class or FRAC group, but the cost of this approach can be expensive in eastern Washington.
- Never exceed more than two QoI applications in sequence. If two sequential applications of a QoI fungicide are made, this “block” should be alternated with at least two applications of one or more fungicides of a different mode of action or FRAC group. When QoI compounds are used as a solo product (Abound, Flint, and Sovran), the number of applications should be no greater than a third of the total number of fungicide applications per season.
- In programs utilizing tank mixes or premixes of a Group 11 fungicide with a fungicide of another group (e.g., Adament or Pristine), the number of Group 11 fungicide (QoI)-containing applications should be no more than half of the total number of fungicide applications per season. It also helps to tank-mix fungicides from different groups that are both effective against powdery mildew. Sulfur is a relatively inexpensive and effective companion product for mixing with medium- or high-risk compounds. Try to include it in every spray tank aimed at powdery mildew, if permitted according to usage instructions on product labels.
Always follow label instructions pertaining to application rates and intervals, and always use a properly calibrated sprayer and sufficient spray volume to provide good coverage.
Critical spray period
The most critical period for powdery mildew control is from immediate prebloom to three weeks postbloom. Our most effective compounds should be utilized during this period. Bloom is also a critical period for the establishment of Botrytis bunch rot in the vineyard. As noted above, several of our highly effective powdery mildew fungicides/fungicide premixes (Adament, Flint, Inspire Super, and Pristine) provide activity against both powdery mildew and bunch rot. These compounds are logical for deployment during bloom, but remember to keep applications of QoI (Group 11) compounds or mixtures containing them to a minimum.
View the Grape fungicides available in 2011 for Washington grape growers to see the full list of registered powdery mildew fungicides available.