Issue link: https://read.dmtmag.com/i/275392
www.goodfruit.com GOOD FRUIT GROWER MARCH 15, 2014 37 part to the region's cold winters and dry summers. Before redleaf virus appeared, Walsh did not recommend spraying grapes if leaf- hopper populations were 18 or fewer per leaf. But the new virus could change the strategy from one of control to eradication. Monitoring for leafhoppers will be more important in the future, he said. Leafhoppers have a simple life cycle. Eggs are deposited on leaves. Adults and nymphs feed on leaves by puncturing leaf cells and sucking up the contents. Feed- ing results in a stippling of the leaves and can reduce photosynthesis. "Adults form clouds in the vineyard," said Walsh. "In Washington, they're really more of a worker nuisance." Anagrus wasps (Anagrus epos) are effi - cient parasitoids of leafhoppers. In some Washington vineyards, the wasps have done a good job of reducing leafhopper num- bers, he reported. Parasitized eggs can be identifi ed by their reddish color. Walsh's previous research showed that looking at leaves with the naked eye is not very effective way to determine population levels. A hand lens is required. Walsh hopes that future research at WSU will allow scientists to use DNA bar coding of leafhoppers, making identifi cation of nymphs quick and reliable. When leafhoppers are in the nymph stage, it's diffi cult to tell the species apart. Using DNA tests could also show which of the two species is prevalent in a vineyard. "We'll need this type of information if we determine that one species is better than the other in vectoring the disease," he said. "It may be that we only need to be concerned about one of the two species. If we could take samples of leafhopper and run them through PCR (polymerase chain reaction) testing, we would know what species we have and how prevalent it is in the fi eld. That will help us better control the disease." Walsh noted that leafhoppers are rel- atively easy to control and are often "col- lateral kill" when growers are controlling grape mealybug in vineyards to prevent the spread of grapevine leafroll disease. Several insecticides are registered for broadcast or chemigation application (see "Leafhopper insecticides for Washington grapes). Walsh said Movento is a new, systemic foliar insecticide that moves up and down the plant. "But it needs to be absorbed by the leaf and metabolized by the plant before becoming toxic to the insect," he stressed. "Grape growers using regulated defi cit irrigation should make sure they use it early in the season before grapevine leaves become old, tough, and hardened." Pyrethroids, a class of insecticides found in many insecticide mixes, should be avoided because they disrupt natu- ral enemies. "My profound hope is that growers avoid pyrethroids because they kill all benefi cials and oftentimes cause bigger problems with other pests, like mites, later in the season," he said. When using chemigation products, growers must also consider soil mois- ture and irrigation schedules, Walsh added. • Consider for your next planting: • BRUCE PONDER • SUSAN WILKINSON • ADAM WEIL • DAVE WEIL 503-538-2131 • FAX: 503-538-7616 info@treeconnect.com www.treeconnect.com BENEFITS: • Disease tolerant • Cold hardy • Adapts well to all cherry-growing districts • Forms flower buds and comes into bearing quicker than Mazzard with a better distribution of flower buds Roots available for SPRING DELIVERY Call Tree Connection: 800-421-4001 Dwarfing Cherry Rootstock Krymsk ® 5 Krymsk ® 6 [cv. VSL-2, USPP 15,723] [cv. LC-52, USPP 16,114] "Krymsk ® 5 and Krymsk ® 6 cherry rootstocks have proven to be the best rootstock for our orchards. They are yield efficient, grow and adapt well, and are cold hardy." —John Morton The Dalles, Oregon Western grape leafhopper. The top image is the adult. The image below is a nymph. PHOTO BY LORRAINE SEYMOUR, WSU PHOTO BY KIRK OLSEN, WSU LEAFHOPPER INSECTICIDES for Washington grapes Broadcast sprays: Lipid biosynthesis inhibitor • Movento (spirotetramat)—spray early in the season when leaf tissues are soft Neonicotinyls • Assail (acetamiprid) • Venom (dinotefuran) • Actara (thiamethoxam) • Clutch (clothianidin) • Provado (imidacloprid) Insect growth regulator • Applaud (buprofezin)—target early nymphs Pyrethroids—disruptive to natural enemies, avoid if possible • Capture (bifenthrin) • Danitol (fenpropathrin) • Baythroid (cyfl uthrin) • Mustang (cypermethrin) Chemigation products—water solubility impacts performance • Venom (dinotefuran)—very water soluble • Platnium (thiamethoxam)— intermediate solubility • Admire (imidacloprid)—not very water soluble