Ministry of Agriculture
Grape Insect and Mite Pests
Grape Mealybug
(Pseudococcus maritimus (Ehrhorn))
- Identification
- Life Cycle and Damage
- Monitoring and Spray Thresholds
- Biological Control
- Cultural Control
- Chemical Control
Prepared by D. Thomas Lowery, Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland.
Mealybug were seldom a concern on grapes prior to the widespread use of synthetic insecticides. Individual bunches of table grapes that touched infested vines would occasionally become infested. Largely due to the detrimental effects of broad-spectrum insecticides on beneficial insects, damaging populations of mealybug have become more common in recent years. As for many other secondary pests, the most important management strategy is to apply chemicals against major pests (leafhoppers, cutworm) only when required and only to portions of the vineyard where control is warranted. Whenever possible, select pesticides that are least damaging to predators and parasites.
Identification
The grape mealybug (Homoptera: Pseudococcidae) 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. Mature wingless females are about 5 mm long. They have long waxy filaments along the edge of the body that are longest at the rear and become progressively shorter toward the front end. Large numbers of eggs are laid in cottony masses. The smaller, winged males have a pair of long, white anal filaments. Yellow to brown crawlers that emerge from the oval, orange eggs are not covered in wax. All stages are mobile.
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| Grapes infested with grape mealybug. Photo courtesy H. Buchler |
Grape mealybug |
Life Cycle and Damage
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 2nd generation that matures in late autumn. They can occur on all plant parts but are more common in summer on leaves and new growth, usually hidden within the canopy.
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 mold fungus. Most fruit damage occurs during the development of the second brood in late summer. Mealybugs can infest grape bunches and are known to transmit certain strains of leafroll virus.
Monitoring and Spray Thresholds
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. A good magnifying glass or dissecting microscope is useful for this purpose. Unlike scale insects, grape mealybug prefer vigorous vines with thick canopies. The need to inspect vineyards for mealybugs can be based partly on past infestations, vigorous growth, and prior use of broad-spectrum insecticides.
Biological Control
Parasitism of grape mealybug has not been studied in British Columbia. Research in California has shown that at least six species of parasitic wasps attack grape mealybug - late summer and fall rates of parasitism often exceed 90%. Predaceous midge larvae attack mealybug egg masses. Lacewings, several species of lady beetles, and many other generalist predators feed on adults. Mealybug and other homopteran insects (scale, whitefly, aphids, etc.) are susceptible to several diseases, including Entomopthora fungus.
Cultural Control
Mealybugs prefer vigorous vines. Ensure adequate nutrition and moisture to produce an optimum crop, but avoid excessive vigour. 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 often escape damage as they 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.
Chemical Control
Malathion, Diazinon and Safer’s Insecticidal Soap can be applied against the crawler stage, while Movento™ (spirotetramat) is active against all stages due to its good systemic activity. Consult the fact sheet, Pest Control Products Recommended for Use on Grapes in British Columbia.
September 2010
