Nothing succeeds like excess. Such is the green peach aphid’s strategy. Able to infest hundreds of plant species, producing up to 80 offspring in a few weeks, and appearing well before its natural enemies, this pest is one of the first on the scene and quickly becomes problematic on garden plants. Green peach aphids are, not surprisingly, light green, though some may be pink or yellow. They have two distinct life cycles: a sexually reproductive life cycle that occurs on stone fruit trees (Prunus spp.) and another, clonal, life cycle in which females give live birth without mating. The clonal offspring are genetically and physically identical young that, in turn, give birth to more clones.
The sexual stage occurs in the fall, allowing the green peach aphid to overwinter as eggs. In protected environments and warmer climates, however, adults are active all year. This is particularly troubling in greenhouses, as they can appear seemingly out of nowhere. Outdoors, the eggs hatch around the same time that peach buds swell, often as early as February. The newly hatched females produce 30 to 80 clones until they become too crowded or their host declines. Then they start producing winged females, which disperse to hundreds of suitable host plants.
These winged aphids are truly nefarious. Moving from plant to plant, they leave a few clones at each stop. Given that clonal offspring are literally born pregnant, just one aphid is an infestation in the making. Furthermore, the winged adults transmit viruses as they move between hosts. Despite being very weak fliers, winged aphids can spread for miles when carried by the wind.
Though aphids have amazing reproductive and dispersive capabilities, they are only ephemeral pests in organic gardens with good floral diversity. Green peach aphids are like candy to their natural enemies. They readily fall prey to parasitic wasps, lady beetles, predatory maggots, and lacewing larvae. Infestations can usually be controlled simply by waiting for beneficial insects to arrive. Early in the season or under glass, they can be dislodged with a strong jet of water or sprayed with an OMRI-listed horticultural soap or oil.
Originally published in Organic Gardening Magazine, February/March 2014.
Illustration: Jack Unruh