Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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Spring 2011
GRAPEGROWING
TABLE I: Males trapped by County and by Flight* (2010)
Traps catches from CDFA Statewide trapping program of European grapevine moth, 2010.
*By flight is estimated because traps were serviced at minimum of 14 day intervals.
Studies of plants in riparian areas have thus far not identified any riparian host of EGVM in Napa County.
Another host of consequence in the Mediterranean region is Daphne gnidium. This host has not been found in North America. Host studies will continue in Napa County in the coming years. In the meantime, management programs will focus on vineyards. Olive flowers may be treated when first generation larvae are developing.
Pheromone-baited traps are an effective monitoring tool in vineyards without mating disruption. There are two types of lure available: 1) a rubber septum impregnated with the pheromone, and 2) a square patch containing a membrane with the pheromone.
Traps baited with rubber septa lures caught significantly more moths for three weeks in the spring when temperatures were at the lowest of the season. Membrane lures caught on average 20% more in the warmer months. Lures should be replaced according to label instructions.
Pheromone-baited delta traps should be placed in a vineyard as bud break approaches and monitored on a weekly basis until harvest. Males do not fly great distances. At least one trap should be deployed for every 10 acres, or one trap per block in parcels smaller than 10 acres. Traps should be oriented such that the base of the trap sits at the top of the grape canopy; traps should be moved up the trellis as the canopy grows.
Mating disruption can be a very effective management tool. Mating disruption technology deploys a synthetic version of the female sex pheromone. It is an organically-acceptable pest management method.
The dispenser registered for use is a twin tube hung in the vineyard (200 per acre). The plumes of synthetic pheromone that are slowly released by the dispensers make it difficult for males to locate females for mating. Delays in mating affect fecundity; ageing females produce fewer eggs.
Unlike insecticides, which kill the same proportion of a population regardless of population size, mating disruption becomes more effective as insect populations get smaller. It can therefore be a very effective
tool for growers managing dwindling insect populations. It can be especially useful during the third generation, since the material does not need to make contact with a life stage to be effective. Mating disruption dispensers should be deployed at or just after bud break.
Insecticides can be used to manage populations during the first and second generations. Available insecticides are active against eggs and larvae (ovicide/larvicide), or strictly against larvae (larvicide). Organic growers have the option of using Bacillus thuringiensis (various products) or spinosad (Entrust®).
It is critical to rotate between different modes of action to avoid or delay development of resistance to these insecticides. Many of the insecticides are reported to be minimally toxic to beneficial insects, although unwarranted applications should be avoided whenever possible.
Conventional growers may apply first generation treatments (1) at or shortly after peak flight; or (2) at egg hatch. Insecticides applied at peak flight should have an ovicide/larvicide activity. Insecticides applied at egg hatch may have ovicide/larvicide or strictly larvicide activity.
If the conventional insecticide is applied at egg hatch and the product residual is sufficient, then only one application should be necessary during the first generation. Organic growers should begin applying insecticides at egg hatch. Depending on the product residual and the length of the flight, two to four applications may be needed for the first generation.
It is important to monitor the flower cluster after an application, especially if a short residue insecticide was applied. Search for webbed nests containing flower parts with abscised flower caps. Tease apart the nests and look for the worm, bites on individual flowers, webbing, and/or excrement.
Conventional growers treating the second generation may make one application of an ovicide/larvicide or a larvicide. Optimal timing for an ovicide/ larvicide application is three to five days after the first moth of the second generation is detected. Optimal timing for a larvicide application is egg hatch (roughly 10 to 14 days after the first moth is detected).
Pheromone dispenser registered for use in mating disruption program.
Organic growers will also begin applications at egg hatch, and may require two applications to cover the length of the generation. Larvae of the third generation are difficult to treat with insecticides because of their habit of burrowing into berries immediately upon emergence from the egg.
Summary
Napa County management programs for EGVM were very successful in 2010. There were no reported crop losses to EGVM feeding damage. Available management tools were very effective, specific, and minimally toxic to non-target arthropods.
Growers took initiative and responsibility to educate themselves and their employees on the biology of the pest, and made appropriately-timed applications of insecticides and mating disruption. Organic growers were able to maintain their certification while also controlling pest populations. Quarantine restrictions were respected and compliance was high.
Future research efforts will focus on validation of predictive models for California, and continued monitoring of potential hosts in riparian and landscape vegetation.
Alternatives to pheromone attractants to monitor vineyards under mating disruption will be explored. Different formulations and timing of organic insecticides to improve efficacy will be investigated. Finally, the fate of larvae during the winemaking process will be evaluated.