Beneficial Bugs for Winegrape Growers
Using and encouraging beneficial insects and mites to control vineyard pests
At the recent Organic Grapegrowing Conference sponsored by the Napa Valley Grapegrowers, two experts talked about introducing these beneficial inspects and planting crops to encourage them. Kim Gallagher-Horton of Biobest Sustainable Crop Management raises beneficial insects (six legs) and predatory mites (arachnids with eight legs) for pest control.
She recommends the “Natural Enemies Handbook” from the University of California, Davis, as a guide to these beneficial creatures, but highlighted a few that kill major vine pests such as spider mites, mealybugs and leafhoppers.
Gallagher-Horton said that predatory mites are some of the most effective predators to release in vineyards for spider mite control. The Western predatory mite, Galendromus occidentalis is native to western North America and found in deciduous orchards and vineyards. The Cali predatory mite Neoseiulus californicus is found throughout California and other locations.
The Cali mite is sensitive to temperatures above 105°F, while the Western version is good to 120°.
Commonly used pesticides kill most of these predatory mites, but the Sterling insectary strain of these predatory mites has been bred to be resistant to many pesticides
G. occidentalis is most effective against web-spinning mites in trees including the Pacific, two-spotted Willamette spider mites and can be an effective predator of European red and citrus red spider mites.
N. californicus is effective against the web-spinning mites and persea mites in vineyards and greenhouses. These predators do not feed on foliage or become pests. If spider mites are not available, they will starve or migrate.
G. occidentalis and N. californicus are produced commercially by growing them on bean plants. When a cut bean plant is placed into the crotch of a vine canopy, the predators will walk off the wilting foliage into the tree or onto the vine. Once they find spider mites, they settle down and reproduce. They can move from vine to vine by walking and by wind currents. These predators can also be purchased in bottles. The bottle is filled with a carrier media (corn grit) and can be sprinkled on to the vines.
When 5% to 15% of sampled leaves are infected with spider mites, it is time to release predatory mites. A release rate of between 2,000 to 5,000 predatory mites per acre is usually enough to initially inoculate a vineyard. Careful follow up sampling can determine if another release is necessary.
Three criteria must be addressed when releasing predatory mites. Release them early in the season to take advantage of their ability to increase rapidly. They must be released when some spider mites are present so that they do not starve and leave your vines. Though less an issue for organic growers, some chemicals can affect the predatory mites. Spider mites often migrate into crops during late March to May.
Heaviest applications are needed around dusty roads and in weak blocks.
Another predator of spider mites is the six-spotted thrip. “It loves spider mites,” said Gallagher-Horton. “Put it in places with high infestation.”
Dealing with mealybugs
Both grape and vine mealybugs are major pests. “You want to eradicate them,” Gallagher-Horton stated. They’re also hard to kill with chemicals because they have waxy coatings that resist absorption.
Two predators kill mealybugs. The aptly named mealybug destroyer beetle (Cryptolaemus montrouzieri) is a cousin of the ladybug, which is also really a beetle.
The destroyer beetle lays its eggs in wooly mealybug masses. The adults and larvae of the mealybug destroyers feed on all stages of the mealybugs. If no mealybugs are around, Cryptolaemus feeds on aphids and scale. The recommended release rate is 500 per acre or one adult per square foot. The beetle is most active in sunlight and when the mealybug population is high. It’s important to control ants when using predators, however, as they will attack predators. Ant bait stations are recommended.
Gallagher-Horton warns that it can take many weeks to control the mealybug population.
Another predator on mealybugs is the anagyrus or vine mealybug parasitoid wasp (Anagyrus pseudococci.) It stings the mealybug and lays an egg in it. This stops the mealybug from feeding, and the wasp larva will consume the mealybug and emerge as an adult.
A recommended release rate is 500 female wasps per acre per month from April until August. They’re effective from the second instar through adult mealybugs. These predators can be used with the mealybug destroyer.
Gallagher-Horton noted that there are no specific predators available for leafhoppers. Among the general predators are green lacewings (Chrysopidea.) Their larvae are vicious carnivores, she noted. But the adults love flowers with pollen.
She also said that the minute pirate bug (Orius) eats anything. Biobest supplies these beneficial and predatory insects and mites.
The right plants will also attract and sustain beneficial creatures. Ann Baker specializes in designing landscapes that do just that.
She recommends planting a diverse ecosystem to reduce the pest concentrations that would exist in a vineyard monoculture. This includes developing plant communities for different areas, soils and light gradients as well as increasing diversity through mutualism and plant synergies.
Baker urged linking habitat areas so they aren’t isolated. She suggests adding insectary plantings in vine rows, avenues, riparian and other natural areas, field edges, utility areas, swales and ditches, road edges, power lines and reservoir banks, ideally at 50-meter intervals.
And also inc rease habitat for diverse bird species; some birds like bluebirds and swallows, are voracious feeders on insects, while raptors consume rodents and other mammalian pests.
She recommends planting local seed mixes, and also culinary herbs, buckwheat, native strawberry and yerba buena. Poppies, sunflowers and umbel family plants (parsley, carrots, Queen Anne’s lace), coyote bush, ceanothus, willow and native oaks are also especially recommended.