What Is Being Done To Prevent Fungicide Resistance in Grapes
June 15, 2021 While the thought of powdery mildew continues to keep grape growers up at night, there are two related issues that cannot be ignored, according to Peter Bierma, President/CEO of Sym-Agro. The first is fungicide resistance, the second is maximum residue limits (MRLs).
Fewer new synthetic solutions are in the pipeline, Bierma says, leading to the overuse of similar Fungicide Resistance Action Committee (FRAC) groups. Further complicating the matter are MRL restrictions that vary from country to country, he adds.
“While biological fungicides are playing a role, most are predominantly preventive products but do provide the same level of reliable disease control and typically have shorter duration of control,” Bierma says. “We see the future more in symbiotic combination strategies, using some contact active materials with plant-resistance products that overlay to provide commercial disease control.”
Nutrien Ag Solutions is developing its fungicide rotation strategy to assure that the company targets the proper disease at the correct timing while making certain to rotate FRAC groups to avoid fungicide resistance, especially to powdery mildew.
“In our experience, resistance can occur due to many external factors,” Nutrien Ag Solutions Crop Consultant Henry Hinkle says. “However, the best method to avoid resistance is to rotate chemistries. Fortunately, new chemistries and fungicides are available that give growers more tools to manage disease while preventing resistance. Throughout the growing season, we’re working with growers to identify these challenges and build the appropriate plan to protect their crop investment and produce a high-quality crop.”
Alternating FRAC groups as well as rotating and tank-mixing contact with systemic fungicides are recommended practices for powdery mildew control, according to Svea Boettcher, Product Manager–Horticulture Fungicides and Biologicals, Bayer Crop Science.
“Even though most growers are experts when it comes to managing their crop, resistance management sometimes does not get the attention it deserves,” Boettcher says.
Best practices to alleviate that problem, Boettcher says, include early start of spraying programs; tighter spray intervals; disease/pest monitoring and quick reaction; product/mode of action rotation; cane and leaf pruning on premium grapes; inclusion of sulfur; and appropriate spray coverage by maintaining the appropriate speed during the application.
Early and frequent scouting is important and frequently overlooked for effective crop management, Hinkle adds.
“Some diseases, like powdery mildew, can be hard to detect early in the season, but frequent scouting combined with field history and local knowledge should be used to manage this and other pathogens,” he says. “Most fungicides are preventive rather than curative; therefore, diseases like powdery mildew are best managed proactively rather than reactively to contain the disease and stop it before it can spread.”
BEYOND POWDERY MILDEW
Alix Whitener, Technical Service Manager, FMC, says one research priority in the Pacific Northwest is to identify and manage the vectors responsible for red blotch disease. In addition, there is still much to learn about grapevine
trunk diseases.
“Some people might not even know there’s a disease complex starting to tank their yield or slowly eat away at new growth in their vineyard because the symptoms can be so subtle,” Whitener says. “Yet trunk diseases can cause a 20% yield loss in 10-year-old vineyards and 70% loss by year 15.”
Largely overlooked, according to Bierma, are all of the effective natural predators that can help with insect and mite management. For grapes, leaf hoppers and mites tend to be a problem when non-selective pesticides or even sulfur are used early in the season.
“Destroying the natural predators effectively takes away the safety net, leading to consistent mid- and late-season outbreaks,” Bierma says. “Protecting and fostering more beneficial predators can substantially manage or reduce pest outbreaks and reduce late-season rescue treatments.”
COMPANY NEWS
Bayer Crop Science: Luna fungicides provide control of powdery mildew and most other prevalent and challenging diseases. Serenade ASO, the company’s biological fungicide, which is also approved for organic use, has proven to be an effective component of disease control programs, the company says.
Certis Biologicals: LifeGard is the first in a new class of biological disease control solutions that switches on the plant’s built-in immune defenses by eliciting an induced resistance (IR) response to help fight against bacterial, viral, and fungal diseases. “Bio-based products offer similar disease spectrum to conventional chemistries with the added benefit of shorter re-entry intervals, i.e., typically four to 12 hours, and with many having a zero-day PHI (preharvest interval),” Mike Allan, Vice President-North America, says. “In addition, biologicals are residue exempt and are an ideal fit in an IPM program.”
FMC: Flutriafol products Rhyme fungicide and Topguard Fungicide Specialty Crop address powdery mildew and other diseases. The active ingredient is efficacious in drip and foliar applications, giving growers flexibility in their fungicide resistance management rotation in grape vines and trees, Whitener says. Rhyme has received a 2(ee) label in California for the management of the wood disease complex on grapes via drip irrigation. When applied via drip, flutriafol is taken up by the roots and moves upward through the plant’s xylem to protect the trunk, cordons, canes, leaves, and new growth.
Nutrien Ag Solutions: Use of the company’s Digital Hub continues to be an area of growth and opportunity, providing growers with a tool to manage their operations and plan their inputs.
“Over the past year, we’ve experienced more growers adopting the Digital Hub to manage their accounts, analyze data, and build their crop plans,” Hinkle says.
Sym-Agro: Unlike biological fungicides, ProBlad Verde is a biochemical with direct disease activity, is translaminar, and works in 10- to 14-day spray intervals. ProBlad Verde is MRL-exempt, which allows treated fruit to enter any global market. “We have two to three new grape materials in the pipeline, all meeting our low-dose, predator-safe, and OMRI-certified criteria,” Bierma adds.
UPL: PH-D Fungicide is a biological fungicide that performs like a conventional fungicide against grape diseases, such as Botrytis bunch rot, summer rot, and powdery mildew, Technical Service Manager Emily Smith says. It is the only FRAC 19 fungicide. Down the line, VACCIPLANT Plant Defense Stimulant will use active biological compounds to stimulate fruit crops’ natural defense mechanisms to boost disease resistance, plant health, and yields.
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