Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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MARCH/APRIL 2010
GRAPEGROWING
If webbing is found, it is important to verify it was caused by a larva and that hatched eggs are also present.
Cool spring temperatures will postpone mating and egg laying. At this time it is not known what effect low temperatures will have on early development of the first generation. Once a degree day model is validated for L. botrana in California, the focus of monitoring guidelines for the first generation may be shifted from egg hatch to egg laying.
In Europe, feeding damage to flower clusters is considered low and researchers in Germany have shown that yield is not reduced. As a result, control measures are not directed toward first generation larvae in Europe. Currently in Chile, the first generation is targeted for control measures which are timed according to the presence of eggs.
Because other lepidopteran pests in California cause webbing in grape flower clusters, California growers will have to verify that larvae found in clusters are L. botrana. To do so, the larvae must be associated with hatched eggs and adult male trap catches.
In California in 2010, an insecticide application directed to the first generation larvae may be advised if eradication efforts are required. Timing is critical for success; growers and PCAs will have to monitor flower clusters for egg hatch. If larvae are observed and verified to be L. botrana, an insecticide can be added to a powdery mildew fungicide application.
Second generation — One week after trapping the first males of both the second and third flights, begin to monitor 100 grape clusters. The berries may be about pea-size when second generation eggs are monitored. Observe a cluster in direct sunlight and look for eggs laid singly on the surfaces of berries. Freshly laid eggs will reflect direct light and appear very shiny and white.
As with the first generation, note the timing of egg development and hatch. An insecticide application with a long residual should be directed to small larvae; thus subsequent larvae are controlled as they emerge from eggs or shortly thereafter.
Third generation — The clusters will be past veraison when eggs are monitoried; eggs will be easier to locate on dark fruit. Note the timing of egg development; as in earlier generations, a treatment must be applied when larvae emerge from eggs.
Sometime in the fall, larvae leave grape clusters and pupate under bark on cordons or the trunk. If the vineyardwas not monitored with traps during the growing season and an infestation is now suspected, examine any grape clusters remaining in a hand-harvested block. Look for the damage caused by third generation larvae (webbing and frass), and larvae inside damaged berries.
A suspect vineyard may also be scouted for pupae in the fall. This is the only avenue available to growers and PCAs for a vineyard that was mechanically harvested.
Management
Insecticides — Male moth flight, egg laying, and egg hatchmust bemonitored in order to correctly time the application of insecticide. Once the larvae begin to web flower parts or feed inside berries, chemical control is less effective. Even though the first generation larvae damage is not of economic importance, if eradication efforts are required or populations are very high, controlling the first generation helps lower population levels in the second generation.
Many insecticides effective against European grapevine moth and other lepidopteran pests have recently been developed. Different classes of insecticides have different modes of action. If more than one insecticide application is needed for the control of L. botrana rotating chemicals with different modes of action may help prevent the development of resistance. The Insecticide Resistance Action Committee (IRAC) assigns a group number to each mode of action. The group number appears on insecticide labels.
The bacterium Bacillus thuringiensis (Bt) produces proteins that are toxic to very specific species of insects. These proteins, once ingested by the insect, act as a stomach poison. The Bt toxin is available in
several commercial products that are specific to Lepidoptera (moths and butterflies).
Given that a larva must ingest the insecticide for it to be effective, it is best to apply when warm sunny days are forecast, especially in spring, because the larvae will tend to be active and feed at warmer temperatures. Two applications of a Bt product are recommended per generation, because egg laying thus larval emergence occur over several weeks. In addition, Bt has a short residual.
Insect growth regulators are effective against many species of lepidopteran insects. These products have lower toxicity to beneficial insects, mites, and pollinators. This class of insecticide prevents the insect from molting into its next growth stage; thus mortality may take several days. If the insect growth regulator affects both the egg and the larvae, application should begin at the start of egg laying rather than at the initiation of egg hatch.
Spinosad products must be ingested by the insect; therefore it has little effect on sucking insects and nontarget predatory insects. It may be toxic to beneficial parasitic wasps if they feed on contaminated honeydew and to honeybees if they come into contact with the spray. There are several commercial spinosad products, both synthetic and organic formulations.
The spinetoram group of pest control chemicals is derived from spinosad that has been chemically modified, resulting in improved insecticidal activity and longer residual activity. However, the longer residual activity may also result in greater toxicity to parasitic wasps.
Other insecticide groups include rynaxypyr, neonicotinoids, pyrethroids, carbamates, and organophosphates. Although each group has a different mode of action, all of these insecticides block the insects’ nerve synapses or the conduction of nerve impulses, ultimately causing muscle paralysis.
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