Green apple aphid
Excerpt from Publication 310, Integrated Pest Management
Table of Contents
The green apple aphid, Aphis pomi (DeGeer), is widely distributed in Canada and the United States and first appears in apple orchards in late May to early June. The insect sucks sap from leaves on water sprouts and succulent terminal growth. Green apple aphids are usually found close to major veins on the underside of the leaf. The green apple aphid also attacks pear, hawthorn, quince, crab apple and spiraea. This aphid is the most predominant one in Ontario apple orchards, but the abundance of natural predators often means chemical controls are not necessary.
Eggs are 1 mm long, shiny, black and oval shaped. Nymphs (Figure 4-13) are 2 mm in length, yellow-green to light green, oval shaped with black cornicles (tail pipes) and have five instars. Adults (Figure 4-14) are 2 mm in length, oval shaped and bright green with black cornicles and legs. Adults can have wings or be wingless. Immature green apple aphids have shorter antennae and less developed cornicles than immature rosy apple aphids, and are usually found in colonies on young terminals of apple trees.
Figure 4-13. Green apple aphid nymph
Figure 4-14. Green apple aphid adult
Green apple aphids overwinter as eggs on suckers at the base of buds on terminal shoots. Eggs hatch when buds burst and the first leaves are unfolding. Newly hatched nymphs are all females. Nymphs begin to feed immediately on developing leaves, and are initially present on terminal shoots, moving later to older cluster leaves. After feeding for about two weeks and molting several times, nymphs mature into wingless adults that reproduce without mating. These adults give birth to live young, with populations building rapidly. Each female can produce 50-100 live offspring. Young aphids develop in 7-10 days. Green apple aphid populations build slowly on apples in early spring (bloom, petal, fall), and more rapidly as average daily temperatures increase. Green apple aphids are most numerous during July and early August. Depending on weather conditions, one generation is completed in two to three weeks. There are many generations per year. Adult aphids in a colony (Figure 4-15) are generally wingless until crowded conditions induce the formation of winged individuals that disperse to new hosts.
Figure 4-15. Green apple aphid colony
Green apple aphids usually remain on apples throughout the summer. In late summer, males are produced as well as females. Females then mate with males and lay overwintering eggs. The greatest numbers of eggs are 15-20 cm from the tips of twigs. Eggs are seldom found on the large scaffold limbs or the trunks of apple trees.
The green apple aphid sucks sap from the leaf. Heavy infestations reduce vigour and growth of shoots - a concern in nurseries and young, non-bearing orchards. Feeding reduces bud size and internodes' length, and causes leaf curling. Aphid damage can stimulate lateral branch growth and affect tree shape. Leaf curling and weakened terminals are susceptible to winter injury. Honeydew produced by the aphids may drip onto fruit allowing sooty fungi to grow. The fungus blemishes fruit and lowers market value. In heavy infestations, green apple aphids feed on immature apples and cause russeting.
Begin monitoring at petal fall and continue until terminals harden off (late July or August). Check 100 terminals in a 4-6 ha block weekly throughout the summer (Figure 4-16). Pick 10 terminals per tree on 10 trees randomly, without visual bias towards infested terminals. The action threshold for green apple aphid is 400-600 aphids per terminal on 10% or more of terminals checked. Be sure to scout for presence of predators when assessing aphid populations in orchards. If more than 20% of the aphid colonies have natural enemies, delay or eliminate an insecticide application. Resample orchards with high numbers of natural enemies present within a week to see if predators are providing control.
Figure 4-16. Scouting green apple aphid
Aphid populations are affected by environmental conditions such as weather, plant health and natural enemies. If aphids do not have access to succulent new growth - and they feed on older leaves - the number of young produced drop by up to 50%. If temperatures are 30-32°C and greater, females do not reproduce well. Aphids die when temperatures remain high for several days, and heavy rains wash aphid populations off leaves. A cool, wet spring favours aphid development and is unfavourable for the aphid's natural enemies.
Green apple aphids are one of the few apple pests often managed by biological control. A number of beneficial insects are effective for biological control in apple orchards. The most commonly observed predator of green apple aphid is Aphidoletes spp. (Cecidomyiidae), an orange maggot midge. Other natural enemies (predators) of apple aphids include hover fly larvae (Syrphidae), lacewing larvae (Chrysoperlidae and Hemerobiidae), lady beetle larvae/adults (Coccinellidae), mullein bug (Miridae), minute pirate bug (Anthocoridae), earwigs and some parasitic wasps (Braconidae). The natural enemy complex can be disrupted by insecticides applied against other pests. When possible use products less likely to disrupt predator populations. See more information on beneficial insects.
Manage nitrogen levels in plants to prevent excessive, lush terminal growth and help reduce aphid populations. Avoid summer pruning until terminal buds have set to prevent re-growth of shoots that are very attractive to aphids. Hand suckering in early June removes unnecessary vegetative growth that attracts green apple aphid. Some research suggests Apogee - a plant hormone growth regulator minimizing terminal growth - creates a less optimum environment for some aphid species.
Insecticide treatments may be necessary in nurseries and young,
non-bearing blocks if populations of green apple aphid become high.
For more information:
Toll Free: 1-877-424-1300