A more serious threat to vineyards than the grape mealybug, the vine mealybug appears in much larger numbers, causes more problems and is more difficult to control. The best way to manage VMB is preventing it from becoming established, reports Roger Duncan, University of California Cooperative Extension farm advisor for Stanislaus County.
It produces more eggs more generations per year than the grape mealybug. Feeding activity by VMB can reduce vine vigor and lead to the collapse of clusters or whole spurs. In addition, the VMB excretes large amounts of a sticky substance, called honeydew. In fact, badly infested clusters can look like they are covered with melted sugar or candle wax.
The combination of feeding damage and honeydew production can lead to sooty mold and bunch rot. The VMB also has the potential to spread some viruses from vine to vine, Duncan notes.
“I encourage grape growers and PCA's to hang pheromone traps in local vineyards to detect if VMB is present, especially if you have planted a new vineyard or replanted vines within the past five years,” he says. “If VMB is verified, come after it with heavy guns and try to eradicate it before it becomes established.”
“The importance of early detection of VMB in your vineyard cannot be overemphasized. Growers should train their crews to identify the damage.”
The VMB is present year-round and can be found on all parts of the vine. During the winter, eggs, crawlers, nymphs and adults are under the bark, within developing buds, and on roots. However, most VMB are on the lower trunk near the soil line and on roots.
As temperatures warm in spring, VMB increase in numbers and become more visible. By late summer, VMB can be found on all portions of the plant, including canes, leaves and clusters.
In checking for VMB as with mealybugs, look for white, cotton-like insects. Egg sacks are under the bark or in grape clusters, only in larger numbers than grape mealybug. Also, check for active ants on the vines as they move mealybugs around and protect them from predators.
If you find any mealybugs, Duncan suggests using a lens to help identify the VMB. Unlike grape, obscure and long-tailed mealybugs VMB have no “tails.”
Ants can move mealybugs short distances and wind can blow infested leaves into adjacent vineyards. But, the VMB can’t fly. Any long distance movement requires the activities of man or birds.
“VMB can hitch a ride on vineyard equipment, mechanical harvesters, people, clothing, picking buckets — just about anything that comes into contact with infested plant parts,” Duncan says. “VMB can also be brought in on infested nursery stock or cuttings. In fact, we suspect this was the primary way VMB was spread through the state.”
He recommends inspecting any equipment coming from other vineyards closely, especially if they have been used in infested counties. Also, clean your own equipment before transporting it to other locations.
If you suspect you have VMB in your vineyard, take a sample to your county Extension office or your county Ag Commissioner’s office or send it to a CDFA lab.