Rosy Apple Aphid in Apple Orchards

Last year we saw very high numbers of Rosy apple aphids in some Ontario orchards early in the season. Rosy apple aphid is a European species of aphid that was first introduced into the US in 1870, and it has since populated most fruit growing regions in the US and Canada. Rosy apple aphid is the most destructive aphid species affecting apples. It is often one of the first aphids to appear in orchards in the spring time.

RAA overwinters in the egg stage in crevices in the bark of larger branches. The eggs hatch and nymphs begin to feed on expanding fruit buds and leaves. Similar to other aphids, RAA nymphs are small soft-bodied insects with piercing and sucking mouthparts and have two distinct cornicles (or tailpipes) projecting from the back of their abdomen. The nymphs are yellow or pink when first hatched, and eventually turn purple in colour. These aphids remain on apples during May, and in smaller numbers in June and July. They feed and reproduce on plantain until fall, when the females move back into orchards to lay their eggs.

RAA nymphs and adults have toxins in their saliva which causes the leaves to curl and turn red in colour. Leaf feeding around fruit can cause stunting and malformation of developing fruit, and prevent fruit abscission at harvest. Rosy apple aphid is rarely found attacking the young and rapidly growing shoots. It restricts itself to the foliage, the flower stalks and the young fruits.

RAA should be monitored from tight cluster through late June by sampling five clusters from 20 trees. A cluster is considered infested if more than 20 aphids are present. Chemical control is only recommended if more than 10% of the fruit clusters are infested.

Researchers in Pennsylvania have established a relationship between the density of the RAA and fruit damage. The number of infested fruit spurs per tree in a 3-minute search at the early pink to pink stage of apple development is directly related to the number of damaged apples per tree at harvest. This relationship assumes that the aphids attack the blossom clusters at random and the aphid-infested cluster yields one injured apple. From this relationship, researchers have proposed that if the grower finds an average of one infested cluster per tree at the pink stage then a chemical treatment is needed. Aphids have many natural enemies including hover fly larvae, lacewing larvae, lady beetle larvae/adults, mullein bug, minute pirate bug, earwigs and some parasitic wasps. The natural enemy complex can be disrupted by insecticides applied against other pests. When possible use softer pesticides which are less likely to disrupt predator populations.