Rosy Apple Aphid
Excerpt from Publication 310, Integrated Pest Management
Table of Contents
The rosy apple aphid, Dysaphis plantaginea (Passerini), is found in most apple-growing regions of North America and is a pest on all apple cultivars. Apple is the preferred host for rosy apple aphid but they also feed on pear and hawthorn. Cortland, Idared and Golden Delicious are most susceptible to injury. This aphid feeds mainly on apple foliage - notably fruiting spurs - causing leaf chlorosis and curling. Their feeding indirectly stunts and deforms fruits in the cluster, making rosy apple aphid the most economically significant aphid species that feeds on apples in Ontario.
Overwintering eggs on bark and twig surfaces are 0.4 mm in length and oval shaped. When first laid, eggs are bright yellow, gradually change to greenish-yellow and eventually black. The nymph passes through five instars, increasing in size from 0.4-2.0 mm. Young nymphs are pale yellow or pink, and become rosy brown or purple as they grow and feed. Nymphs have long cornicles at the base of the abdomen and long antennae extending almost half the length of the body (Figure 4-17). Adults are winged or wingless and 3 mm in length. In early spring, rosy apple aphids move to developing fruit clusters and become reproductive adults during bloom, taking two to three weeks to mature. Hatched nymphs are wingless females called stem mothers when they mature. Adults are a dark purple-pink and found in colonies on extension and terminal growth.
Females deposit eggs on bark - especially at the base of the buds - in the fall. Eggs begin to hatch as tree buds open in the spring and continue hatching over a two-week period. Nymphs feed on the outside of leaf and fruit buds until leaves
Mature females produce live young shortly after or during bloom. The second generation matures and produces live young two to three weeks after petal fall. Populations are usually greatest in the inner and upper parts of the canopy. The second generation requires 4-40 days to reach maturity and produce young. Unmated females produce live young (parthogenesis) and only females are produced during the summer. Most second generation rosy apple aphids are wingless females. Each female produces 120-185 offspring. There are generally three generations of rosy apple aphid produced on apple, with the second generation occurring two to three weeks after petal fall and the third generation appearing by mid to late June. By early to mid July, most aphids have developed wings and dispersed to summer hosts such as narrow-leaf and broadleaf plaintain or dock. In some seasons, wingless females of the third generation produce a fourth generation on apple. Some areas have recently experienced damaging populations of rosy apple aphid in orchards in mid to late summer. It is not known whether this change in behaviour is due to change in habitat, or lack of need for an alternative host.
Several more generations develop on summer hosts until fall, when winged females return to apple trees and produce live female young. These females develop on apple, mate with males, and deposit eggs that overwinter the following spring.
Young aphids hatch in spring, damaging the outside of fruit and leaf buds by sucking sap from tissues. During feeding, aphids inject a toxin that deforms leaves (Figure 4-18) and fruit (Figure 4-19). Aphid feeding tightly curls and puckers leaves, hiding the aphid colony. Rosy apple aphids produce honeydew that drips onto leaves and fruit. Sooty fungus colonizes the honeydew, and fruit discolours them. Often ant feeding on honeydew is associated with aphid colonies. The most serious rosy apple aphid damage occurs when saliva translocates from the leaves to fruit, causing apples to remain small, deformed (pigmy fruit) and unmarketable. Toxic saliva reduces growth of roots and other woody tissue - and research shows this has an important impact on young trees as they develop a mature bearing structure. Toxins in aphid saliva serve as a "stop drop," preventing the fruit's abscission (natural separation from the tree) at normal harvest. Rosy apple aphid is rarely found attacking young and rapidly growing shoots, restricting itself to foliage, flower stalks and young fruits.
Check for rosy apple aphids every week, beginning at tight cluster and continue until late June. Cortland, Ida Red and Golden Delicious are all susceptible cultivars to monitor for rosy apple aphid. For every 10-15 ha, examine 5 clusters from each of 20 trees for dwarf and semi dwarf plantings. For larger trees, examine 10 fruit clusters from each of 10 trees. A cluster is considered infested if more than 20 aphids are present. Check the interior portion of the tree - where rosy apple aphids usually appear first.
Chemical control is recommended if more than 5% of fruit clusters are infested and few predators are identified. Monitor for aphid predators around rosy apple aphid colonies. Predators may make chemical control unnecessary.
Researchers in Pennsylvania established a relationship between the density of rosy apple aphid and fruit damage. The number of infested fruit spurs per tree in a three minute search at the early pink to pink stage of apple development directly relates to the number of damaged apples per tree at harvest. This relationship assumes aphids attack blossom clusters at random and each aphid-infested cluster yields one injured apple. From this relationship, researchers propose that if a grower finds an average of one infested cluster per tree at the pink stage, chemical treatment is needed.
Aphids have many natural enemies including 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). Pictures and descriptions of these predators and parasites are found in the beneficial insects. The natural enemy complex can be disrupted by insecticides applied against other pests. When possible, use pesticides less likely to disrupt predator populations.
Unpruned trees provide favorable conditions for aphids and greatly limit effectiveness of control. A cool, wet spring also favours aphid development by providing conditions unfavorable for aphid parasites and predators. Aphids are killed by extreme temperatures (low temperature or sudden changes during the winter or hatching period), moisture (cold rains at or just before hatching time can kill young aphids), and predaceous insects and birds. If chemical control is justified, apply insecticide in high volumes of water for good coverage. If possible, spray only susceptible cultivars where the threshold has been reached. Detect rosy apple aphid infestations early, before mid June. Avoid late season applications when chemical has little chance of contacting aphid colonies once leaves are curled. Systemic pesticides are required to control rosy apple aphid once leaf curling has occurred.
Dormant oil sprays to control European fruit scale or San Jose scale can suppress rosy apple aphid by killing overwintering eggs.
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