II. Hosts: GPA has a diverse host range of over 875 species of plants, including all stone fruits and many ornamental shrubs and vegetables.
III. Description: Typical of other aphids, this species is pear-shaped, with long antennae and a pair of cornicles ("tailpipes") extending from the posterior end of the body. Wingless adults (photo above) and nymphs are yellowish-green with three darker green lines on the top of the abdomen. Winged adults also have a yellowish-green abdomen, but the head and thorax (area where wings attach) is dark. Adults are about 1/10 inch (2 mm) in length. Eggs are oblong and shiny black.
IV. Biology: This aphid has a complex life cycle with numerous forms. It overwinters in the mid-Atlantic region primarily as wingless females in protected places on the tree and ground. In the northern areas of this region the winter may also be passed as eggs beneath the buds of stone fruit trees. Aphid feeding on flower parts or on the underside of leaves is usually first observed during the late bloom to petal fall stage. Two to three generations of wingless female aphids are produced in which adults give birth to living young without mating. Populations usually peak shortly after shuck-fall and tend to be most abundant during cool, wet springs and on trees with excessive vigor. Beginning at shuck-fall, and continuing for 4 to 6 weeks, aphids leave the trees as winged females are produced which migrate to numerous vegetables and ornamental plants. In the fall winged migrants are produced on summer hosts; these migrants return to stone fruits. A generation of wingless females is produced which fall to the ground with leaf drop and overwinter. In northern areas, sexual forms (males and females) are produced which mate and lay overwintering eggs on the tree.
V. Injury: Aphids feed primarily on the underside of leaves which causes them to curl (Plate 115), become distorted and yellow, and drop prematurely from the tree. Feeding may also occur on flowers (Plate 116) and fruit (photo below) resulting in distortion and drop. When abundant, aphid feeding results in excretion of large amounts of honeydew which supports the growth of a black sooty fungus that causes spotting of leaves and fruit. This aphid may also serve as a vector of virus diseases to stone fruits. Green peach aphid is one of several aphids that can transmit plum pox virus. This is a major disease of peaches and nectarines which was confirmed in Pennsylvania in October 1999. This is the only record in North America.
VI. Monitoring: To detect GPA presence focus inspection primarily on the underside of leaves from petal fall until about one month after shuck-fall. Flower parts and developing fruit should also be inspected, but aphids are likely to be more abundant on leaves. Throughout most of the mid-Atlantic region, aphids are likely to be detected first on a root sucker or on a small cluster of leaves attached to the trunk or scaffold limb in the lower center of trees. Since effective management requires early detection, frequent monitoring around petal fall is important.
Treatment is recommended on bearing peach trees
there are more than two colonies per tree by petal fall to shuck-split,
or more than five colonies per tree by mid to late May. Because of the
greater potential for fruit damage on nectarine, no more than one
per tree should be tolerated at any time on bearing trees of this fruit.