By Dr. Henry Wu, Technical Sales Support Representative, Chemtura AgroSolutions
Your focus may be on this year’s harvest, but it’s also essential to keep an eye on the future. Good pest management strategies enable you to do both, since they help ensure a high-quality crop while protecting vines and next year’s production all at the same time.
Growers, particularly those with raisin grapes, still need to be on the lookout for several species of spider mites, including: the Willamette mite: Eotetranychus willamette, the Pacific mite: Tetranychus pacificus, and the Two-spotted mite: Tetranychus urticae.
Raisin grape vines are particularly vulnerable to mites pre-harvest because water supplies will be cut off to allow for harvest and crop drying. This stresses the vines and gives mites an edge. Growers need to be sure to effectively deal with any mite problems before harvest begins to protect vines and next season’s production.
Growers should consider using a miticide with fast knockdown and acceptable re-entry and pre-harvest intervals. A product like Acramite® 50WS can be very helpful in these situations by combining powerful knockdown of key mite species with a preharvest 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 preharvest 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 percent 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. Then allow considerable dry down at harvest.
Don’t forget about mealybugs
Mites aren’t the only pre-harvest pest concern.
Now is also the time to monitor vines for mealybugs, which have become more of a problem in wine and raisin grapes in recent years — even more so than grape and variegated leafhoppers.
Harvest is when many grape growers discover mealybug infestations. Be sure to check clusters for them and determine if they have moved into the bark of the vines. Because several different species may infest grapevines, it is important to know which species of mealybug is present because management programs for the various mealybugs differ.
According to experts at the University of California, damage by the vine mealybug is similar to that of other grape-infesting mealybugs in that it produces honeydew that drops onto the bunches and other vine parts and serves as a substrate for black sooty mold. If ants are not present, a vine with a large population of this pest can have so much honeydew that it resembles candle wax.
Also, the mealybug itself will be found infesting bunches, making them unfit for consumption. Like the grape, obscure, and longtailed mealybugs, vine mealybugs can transmit grape viruses.
Follow recommended treatment programs for mealybug infestations. Also, mark affected vines with flagging tape so that you know where to target additional pest management strategies in the spring.
For more information about Acramite 50WS or other pest management solutions, visit Chemtura AgroSolutions.