Previously, grape mealybug (Pseudococcus maritimus) was not considered to be a major pest of grapes grown in B.C. Numbers were generally quite low due to the activity of parasitoids and predators, and direct feeding damage is of little concern. Individual bunches of table grapes touching infested vines would occasionally become infested, resulting in fruit coated with sticky honeydew that reduced their marketability.
The recent recognition that mealybug and soft scale are responsible for the sometimes rapid spread of grapevine leafroll-associated viruses has raised their status to that of major pests. Recent research on grapevine virus vectors indicates that grape mealybug is uncommon north of Oliver.
Largely due to changes in insecticide use, damaging populations of mealybug have become more common in recent years. Whenever possible, apply chemicals against major pests (leafhoppers, cutworm) of grapes only when required and only to portions of the vineyard where control is warranted, using pesticides that are least damaging to predators and parasitoids.
The grape mealybug has a flattened, oval pink body covered in a mealy white wax coating. It is somewhat segmented in appearance, but the divisions between head, thorax and abdomen are not distinct.
The mature wingless females are about 5 mm long. They have long, waxy filaments along the edge of the body that become progressively shorter toward the head. The smaller, winged males have antennae that are half as long as their body and a pair of long, white anal filaments.
Large numbers of eggs (50-800) are laid in cottony masses. Yellow to brown crawlers that emerge from the oval, orange eggs are not covered in wax. All stages are mobile, though the crawlers are the most mobile stage.
Females move in late fall to old wood and lay overwintering eggs in cottony egg masses under loose bark. Crawlers, some of which might have hatched in fall and remained dormant throughout the winter, move to new shoots in spring.
Grape mealybugs mature around mid-summer and produce a second generation that matures in late autumn. They can occur on all aerial parts of the vines but are more common in summer on leaves and new growth, usually hidden within the canopy.
Direct damage is similar to that for soft scale. Plant sap is removed during feeding, and large amounts of honeydew foul the fruit and promote the growth of sooty mould fungus.
Mealybugs can infest table grape bunches during the development of the second brood in summer, reducing their marketability.
Relevant to the spread of leafroll viruses, the small crawler stage is mobile and active, and they can be carried on the wind. Mealybugs can also be transported during mechanical harvesting or field operations and on workers or plant material.
To detect when crawlers are active, remove the loose bark in an area near the infestation and encircle the vine with clear tape applied sticky side out, or use double sided adhesive. Replace the tape every three or four days and check for the yellowish-brown crawlers. Separating mealybug crawlers from soft scale crawlers is difficult and requires a good dissecting microscope.
Inspect vines for the cottony egg masses; leaves coated with shiny, sticky honeydew; and the presence of attendant ants travelling up and down the vine trunks.
The need to inspect vineyards for mealybugs can be based partly on past infestations and prior use of broad-spectrum insecticides. Grape mealybug prefer vigorous vines with thick canopies.
Parasitism of grape mealybug has not been studied in any detail in B.C. However, a parasitic wasp formerly introduced into Canada from California for mealybug biological control was recently reared from grape mealybugs in the Okanagan.
Based on the literature, more species of mealybug parasitoids are undoubtedly active in B.C. Research in California has shown that at least six species of small parasitic wasps attack mealybug, with late summer and fall rates of parasitism often exceeding 90%.
Silver flies were also recently reared from grape mealybug egg masses in the Okanagan where it was observed the larvae consumed a large portion of the eggs.
Other natural enemies of grape mealybug are predaceous midge larvae that feed on eggs and several species of lady beetles and other generalist predators that prey on nymphs and adults. Mealybug are susceptible to several diseases, including Entomopthora fungus.
Mealybugs prefer vigorous vines. Ensure adequate nutrition and moisture to produce an optimum crop but avoid excessive vigor.
Research in California has shown that fruit on cane-pruned varieties is less likely to suffer damage compared with spur-pruned vines. Clusters on cane-pruned vines hang farther away from the mealybug overwintering sites on old wood. Earlier varieties are not exposed to honeydew to the same extent as later varieties.
Heavy infestations of mealybugs and other honeydew-producing pests of grape are usually tended by ants that feed on the sugary excretion and protect the mealybugs from predation. Control of ants can often contribute to a significant decline in mealybug numbers.
For small backyard plantings with an isolated infestation, painting a sticky material around vine trunks and posts and ensuring that ants cannot gain access to the mealybugs often eliminates the problem.
Trials in California have also shown that sprays directed against the Argentine ant (Iridomyrmex humilis) controlled damaging populations of the obscure mealybug (Pseudococcus affinis). Insecticides are not currently registered for the control of ants in B.C. vineyards. For more information about pesticides, see the Pesticides page.
