Green Peach Aphid

The green peach aphid is rather slender in form, light green or yellowish in color. Winged adults of the green peach aphid are pale or bright green and black, with a large dusky blotch on the dorsum of the abdomen. The immature forms are yellow, pinkish, or pale green. The mature wingless forms are pale or bright green and have no waxy covering. The tubercles at the base of the antennae grow towards each other. Populations tend to start on lower leaves and move up the plant. The green peach aphid occurs throughout California and has a wide host range.

In desert areas, Watermelon mosaic virus, Zucchini yellow mosaic, and Papaya ringspot virus are transmitted chiefly by the green peach aphid. This aphid moves into melon fields in large numbers from surrounding vegetation, carrying viruses as it moves and feeds from one plant to another. In the San Joaquin Valley, cucumber mosaic, zucchini mosaic, and watermelon mosaic are often the most important viruses transmitted by this aphid.

Silver reflective mulches have successfully been used to repel aphids from plants, thus reducing or delaying virus transmission. In some areas of the state, row covers have also been successfully used. Biological control can have a significant impact on aphid population, so be sure to evaluate predator and parasite populations when making treatment decisions.

Naturally occurring populations of the convergent lady beetle, Hippodamia convergens, may provide effective control in early spring. Releases of this beetle are not effective, however, because it generally does not remain in the field following release. Other general predators, such as lacewing and syrphid larvae, and parasitic wasps, including Aphidius, Diaeretiella, and Aphelinus species, also attack aphids. Biological control is not effective in reducing virus transmission by this aphid.

• In desert production areas, exclude aphids by applying row covers at planting and removing them at first bloom or earlier. Do not apply row covers in the San Joaquin Valley.
  • Plastic row cover. Do not remove the entire cover at one time because the drastic reduction in humidity will shock plants and can lead to collapse. Instead, vent the covers and remove them piecemeal. If the air temperature under the row cover reaches 104°F remove them. Also remove the row cover before plants grow high enough to touch hot plastic.
  • Spun-bonded row cover. Covers made of spun-bonded materials do not need venting because hot air is able to escape.
• Apply silver reflective plastic mulches at planting to repel aphids from plants, thereby reducing or delaying virus infection. Reflective mulches help plants get off to a healthy start, and are effective until expanding foliage covers the reflective surface. Remove mulches in the desert areas when summer temperatures are excessive for optimal growth of plants. However, in the Central Valley and cooler areas, mulches have not caused plant damage in the summer; in fact, they improve soil moisture and nutrient retention, which may further aid plant productivity.
• Control weeds along ditch banks, roads, in farmyards, and other noncultivated areas that contribute directly to the aphid problem.
• Planting a habitat for beneficial insects, such as sweet alyssum, around the field may be helpful.
• Delay planting until warm temperatures (80° to 85°F) occur and the spring flight of aphids is over.
• Do not overfertilize with nitrogen.
• Fields infested with green peach aphid should be disced or plowed under as soon as harvest is complete.

Biological and cultural controls and applications of insecticidal soaps and certain narrow range oils are acceptable to use in an organically certified crop.

Before planting seed or transplants, set out yellow sticky cards at field edges to monitor the movement of aphids and whiteflies into the crop. Start checking traps after transplanting or when seedlings emerge. When aphids are observed on traps, begin monitoring crop foliage.

The decision to apply insecticides for aphids is based mainly on visual counts; measurable thresholds have not been researched. It is important to treat early to ensure that the aphids do not build up to high levels. Early treatment does not prevent virus introduction; insecticides, however, may help reduce spread of the virus if aphid colonies are present. Be aware, however, that parasites and predators, if present, may prevent an infestation from becoming established throughout a field, thus eliminating the need for insecticides.