Plum and prune-Grape mealybug

Pseudococcus maritimus

Pest description and crop damage The newly-hatched nymphs (or crawlers) are purplish and covered with a powdery wax coating. As the nymphs get older, the coating gets thicker, a fringe of wax filaments develops and the nymphs become more sedentary. The adult female is wingless and looks similar to a nymph. The adult female can be up to 3/16 inch long and has a well-developed ring of waxy filaments around the sides of her body. Mealybug damage results from the honeydew this insect excretes. Honeydew is cast off in small droplets, rains down through the canopy and collects on plant surfaces beneath which can promote the growth of sooty mold.

Biology and life history Grape mealybug overwinters 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 at the base of buds. As buds open, crawlers go directly to new shoots and leaves. Once settled, the crawlers start feeding and become progressively harder to kill as they develop the wax coating. First generation nymphs mature during late June and July in the Pacific Northwest. For each generation, winged adult males emerge first. Later, wingless female mealybugs emerge and release a pheromone to attract males. Then the 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.

Management-biological control

Few reports are available on the effectiveness of natural enemies in keeping mealybug populations at levels below economic damage in the PNW. Parasitic wasps, predatory bugs, predatory beetles, lacewings, and spiders can take a considerable toll of mealybugs when few broad-spectrum chemicals are used. A lady beetle, known as the "mealybug destroyer" (Cryptolaemus montrouzieri), is considered an effective predator of mealybugs worldwide. It is available from some commercial insectaries.

Management-chemical control: HOME USE

  • acetamiprid-Toxic to bees.
  • azadirachtin (neem oil)-Plum only. 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

Prebloom spray

  • diazinon (Diazinon 50W) at 1 lb/100 gal water (4 lb/A). REI 4 days. Do not exceed one in-season application per growing season.

Spring and summer spray

  • acetamiprid (Assail 30SG) at 8 oz/A. REI 12 hr. PHI 7 days.
  • imidacloprid (Prey 1.6F, Nuprid 1.6F) at 4 to 8 fl oz/A. REI 12 hr. PHI 7 days. Warning: Toxic to bees. Do not use until pollination is complete and bees have left the orchard.
  • spirotetramat (Movento, Ultor)-Product formulations vary, check label for rates. REI 24 hr. PHI 7 days.