Green Peach and Potato Aphids

The potato aphid and the green peach aphid are commonly found on many crops including spinach; of the two, green peach aphid is more important. Green peach aphids are dark green to yellow and have no waxy covering. The tubercles (base of the antennae) are slanted toward each other. Populations start on the lower leaves, move up the plant, and are spread over the plant.

Potato aphids have both pink and green forms. This aphid is much bigger than the green peach aphid, and the adult has much longer cornicles (projections at the posterior end of the abdomen) and cauda (posterior tip of the abdomen). Potato aphid colonies are composed of adults with offspring closely clustered around them, usually on the youngest leaves. The potato aphid may occur alone, or in colonies with green peach aphid.

High numbers of aphids can stunt seedlings and will contaminate product bound for market. Green peach aphids vector several viruses that may affect spinach.

Important aphid predators include the convergent lady beetle, Coccinella lady beetles, syrphid flies and lacewings. Epidemics of a disease caused by the fungus Entomophthora aphidis may also kill portions of the green peach aphid population under some conditions. Parasites, including Lysiphlebus testaceipes, Aphidius matricariae, and Aphelinus semiflavus, attack these pests. However, natural enemies rarely provide adequate control of high field populations of the aphid in spring or fall crops.

Some row covers (plastic tunnels or Remay-type enclosures) have reduced aphid populations to below economic levels, but the costs are substantial and the economic viability for large- or even small-scale plantings has not been established. Controlling dust is important to facilitate parasite and predator activity. Aphids tend to be especially high in plants that receive an excess of nitrogen fertilizer.

Biological control and sprays of insecticidal soaps are acceptable for use on organically grown produce.

Check all areas of the field twice a week, but especially the edges, which are usually the first area to become infested. Because infestations are clumped, be sure to sample several plants in many areas of the field.

If high populations develop on seedlings, treat as soon as plants appear stressed. If a significant percentage of plants are infested just before harvest, treat to keep aphids from becoming a contamination problem. Continue monitoring to see whether another treatment is needed. Some populations of green peach aphid may be resistant to certain insecticides in your area; check with your farm advisor for more information.