Dr. Walter Bentley, integrated pest management entomologist at the Kearney Agricultural Research and Extension Center, and Dr. Henry Wu, technical sales support representative for Chemtura AgroSolutions, share their pre-harvest tips for raisin and wine grape growers.
“Pre-harvest preparations—especially pest management—are important for a high-quality product and can also help set the stage for a successful season the following year,” says Wu.
Pre-Harvest Pest Management
“Late-season vineyard management looks slightly different depending on the type of grape you’re dealing with,” says Bentley. “But from a pest control perspective, growers need to watch for mealybugs and mites.”
In both wine and raisin grapes, mealybugs are becoming more and more of a problem to the point that they have replaced grape and variegated leafhoppers as major pests, observes Bentley.
Harvest is often the first time grape growers realize they have mealybugs. “Check clusters for infestation and for mealybugs moving into the bark of the vines,” says Bentley. “If vine mealybugs are the culprit, consider using a contact insecticide in those areas after harvest.” Post-harvest insecticide treatment for grape mealybug is not effective because they are in the overwintering egg stage beneath the bark, he adds.
In those vineyards where either mealybug species is found, Bentley recommends marking the infested vines with flagging tape. The following spring, control should be focused especially on the marked areas if not the whole vineyard.
“Marking vines is a good way to recognize the movement of a pest that moves slowly,” says Bentley. “Mealybugs don’t fly, so they have to be brought into the vineyard by animals or people. This results in spotty infestations. If you can initiate control on those spot infestations before they spread, you can go a long way toward eliminating the pest in your vineyard along with the grape leafroll virus transmitted by the mealybugs.”
In raisin grape vineyards, growers need to carefully monitor mite populations. Raisin grape vines are especially vulnerable to mites at this time because their water supply will be cut off to allow for harvest and crop drying. Lack of water stresses the vines, so growers need to clean up any mite problems before harvest begins.
“Growers should consider using a miticide with fast knockdown and acceptable re-entry and pre-harvest intervals,” says Wu. “A product like Acramite® 50WS can be very helpful in these situations by combining powerful knockdown of key mite species with a pre-harvest interval of 14 days and re-entry interval of only 12 hours.”
Short re-entry intervals allow growers to manage late-season pests without delaying other important pre-harvest activities, such as weed control or terracing.
Raisin growers using terrace drying versus on-vine drying should prepare terraces a few days before harvest. The University of California recommends ensuring soil is dry and free of clods, cleaning up weeds with cultivation and herbicides, and aiming for an 8 to 17 percent slope.
“In wine grape vineyards, growers should irrigate once or twice before harvest to prevent excessive defoliation so grapes can reach desired Brix, pH, total acidity, sugar/acid ratio, and tannin levels,” Wu says. “Then allow considerable dry down at harvest.”