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Aphid: Apple aphid, spirea aphid

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Aphis pomi, A. spiraecola

Overview

in the spring and early summer, both aphid species infest young trees, water sprouts, and vigorous terminals on apple, pear, and quince. Unlike rosy apple aphids, which spend part of their life cycle on plantain, both green apple aphid and spirea aphid remain on apple year-round.

Aphid nymphs and adults suck sap from apple leaves, favoring rapidly growing terminal and water sprout foliage. Leaf curling indicates aphid presence, but causes little or no damage. Aphids excrete large amounts of honeydew which may collect on fruit and foliage. Black sooty-mold fungus can develop on honeydew, discoloring fruit.

Biology

  • Apple aphid and spirea aphid overwinter as black, shiny eggs on the rough areas (leaf and pruning scars, terminals, and spurs) of the bark of the previous season's growth. Eggs hatch in spring and nymphs (all of which are females, called "stem mothers") mature while feeding on developing foliage.
  • Aphid adults are a uniform yellowish-green to green color with black cornicles at the end of the abdomen.
  • The "stem mothers" feed, mature, and produce another generation of live nymphs, all of which are females. This type of reproduction without mating is called parthenogenesis. Eventually, winged aphids ("alates") appear, and for the duration of the summer, the population consists of both winged and wingless parthenogenetic females that continue to produce live nymphs.
  • In late summer, the winged aphids disperse to different apple trees or other host plants and produce nymphs that develop into true sexual forms. After mating with males, females lay overwintering eggs that hatch the following spring. the cycle then repeats itself.
  • Apple aphids and spirea aphids are similar in appearance, but spirea aphids may remain active on apple trees later into the summer.
  • A different aphid, the apple grain aphid, can become very abundant on buds in early spring, but it causes no damage to apples and soon migrates to grain and grasses for the summer. Apple grain aphids are green with a dark stripe on its back.

Monitoring

  • Aphid monitoring should begin in June by checking at least 10 terminals and water sprouts per tree and 10 trees per block. Treatment threshold is 50% of vegetative terminals infested AND less than 20% of infested terminals with biocontrol agents present OR 10% of fruit with honeydew or aphids.

Management

  • Limit nitrogen fertilization to the level necessary for optimum tree growth.
  • Summer prune to remove water sprouts.
  • Two predators offer excellent potential for biological control and can often be found among aphid colonies. Syrphid fly larvae are small, legless, tan-green mottled maggots and Cecidomyiid fly larvae are small, orange maggots. Both are voracious feeders, capable of consuming dozens of aphids before completing development
  • If finding aphid populations above threshold, consider waiting one week and then check again for biocontrol agents. If treatment threshold is still exceeded, apply an insecticide.