Pest description and crop damage The nymphs (or crawlers) are purplish and covered with a powdery wax coating. As they get older, the coating gets thicker, and a fringe of wax filaments develops. The adult female is wingless and looks similar to a nymph. It can be up to 0.1875 (3/16) inch long. It has a well-developed ring of waxy filaments around the sides of its body. Mealybugs cause damage by secreting honeydew. Honeydew is cast off in small drops and falls down through the canopy. When it lands on fruit it causes a coarse, black russet, which is similar to pear psylla russeting. However, mealybug russeting is scattered over the fruit surface, while honeydew from psylla is in patches or streaks.
Biology and life history Grape mealybug overwinter as crawlers in egg sacs beneath bark scales and in cracks. Crawlers start emerging from egg sacs at the beginning of bud swell and begin feeding on the base of buds. When buds open, the crawlers go directly to new shoots and leaves. Once settled, the crawlers start feeding and become progressively harder to kill. First generation nymphs mature during late June and July in the Pacific Northwest. Adult males appear first, mate with last instar nymphs or adult females and die. Receptive females release a pheromone to attract males. Mated females migrate to sheltered areas, lay eggs and die in the egg sac. A partial second generation matures in late August and September. Nymphs of this generation sometimes settle in or around the fruit calyx.
Little research has been done to date on the effectiveness of natural enemies in keeping mealybug populations at levels below economic damage. Parasitic wasps, predatory bugs, predatory beetles, lacewings, and spiders can take a considerable toll on mealybugs. A lady beetle, the "mealybug destroyer" (Cryptolaemus montrouzieri), is considered an effective predator of mealybugs worldwide. It is available from some insectaries.
Management-chemical control: HOME USE
Stages 5-6: Pink spray, spring and summer
- azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
- pyrethrins-Highly toxic to bees. Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
Stages 5-6: Pink spray
- buprofezin (Centaur WDG) at 34.5 oz/A as a ground application using a minimum of 20 gal water per acre. Do not make more than one application per growing season. REI 12 hr. [Group 16]
- diazinon (Diazinon 50W) 2 to 4 lb/A in up to 100 gal water per application. Dormant or delayed dormant use of diazinon is limited to one application per season. REI 4 days. [Group 1B]
Spring and summer
- acetamiprid (Assail 70WP) at 1.7 to 3.4 oz/A in up to 100 gal water per application. Do not make more than four applications per year or exceed 13.5 oz/A per growing season. REI 12 hr. PHI 7 days.[Group 4A]
- buprofezin (Centaur WDG) at 34.5 oz/A as a ground application using a minimum of 20 gal water per acre. Do not make more than one application per growing season. REI 12 hr. PHI 14 days. [Group 16]
- Chromobacterium subtsugae (Grandevo) at 2 to 3 lb/A. Under heavy pest populations, apply a knockdown insecticide prior to or in a tank mix, use the higher label rates, shorten the spray interval, and/or increase the spray volume to improve coverage. REI 4 hr. PHI 0 day. OMRI-listed for organic use.
- diazinon (Diazinon 50W) at 4 lb/A in up to 100 gal water per application. Do not apply more than one in-season application per season. REI 4 days. PHI 21 days. [Group 1B]