Green Peach Aphid

Green peach aphid is among the most common aphid species found on sugarbeet. The aphid may be present at any time throughout the year but is most common in the Imperial Valley from December through April. Generally its color is pale green, although at times individuals may be present that are pinkish. During cool weather, individuals are usually more deeply pigmented and may be confused with the potato aphid (see section on Other Aphids), but the two can be distinguished on close examination. The frontal tubercles at the base of the antennae in the green peach aphid are very prominent and convergent. The potato aphid is much larger than the green peach aphid with longer legs, antennae, and cornicles. While they do have prominent frontal tubercles, they are divergent, not convergent as in the green peach aphid. Winged forms of the green peach aphid have a distinct dark patch on the top of the abdomen; wingless forms lack this dark patch.

Injury caused by the green peach aphid is mainly through its ability to transmit a number of destructive beet viruses. It is the principal vector of Beet yellows virus, Beet western yellows virus, and Beet mosaic virus. It does not transmit Curly top virus, Lettuce chlorosis virus, or Rhizomania (Beet necrotic yellow vein virus).

Green peach aphid can also damage the plant by sucking plant sap. When damaging levels occur, large numbers of aphids can be found on the underside of leaves. Extensive feeding causes plants to turn yellow and the leaves to curl downward and inward from the edges. Aphid damage is most prominent on newer, younger leaves in the center of the plant.

The principal way of reducing virus transmission by the green peach aphid is adherence to the beet-free restrictions and planting dates established by grower and processor agreement. These planting date restrictions are established to avoid planting during major aphid flights and to prevent the virus source (i.e., infected sugarbeet plants), from bridging the time between old and new plantings. Planting date restrictions and beet-free periods vary considerably from location to location; contact your farm advisor, processor, or the California Beet Growers Association for the latest restrictions in your area. Strict adherence to these restrictions is absolutely necessary in order to reduce the amount of virus.

A second, and equally important factor in reducing virus spread, is good field sanitation. Infected keeper beets that produce new vegetative growth after harvest act as sources of virus inoculum for new plantings. Following harvest, thoroughly disc fields and chop remaining beets into small pieces. Watch fields closely and redisc if new growth appears. Take special care where keeper beets resprout in other crops, such as cereals or alfalfa. In such cases, herbicides may be required to control the new growth in order to reduce virus inoculum. These measures help control the incidence and spread of viruses transmitted by green peach aphid but do little in controlling the aphid itself.

Green peach aphid is attacked by a number of common predators and parasites and is susceptible to the fungus disease that commonly attacks aphids. Aphid sampling should always include an evaluation of the presence and activity of natural enemies.

Treatment of aphids to prevent or reduce the incidence of beet viruses is of little value and is not recommended. Treatment thresholds for green peach aphid, as a pest in its own right, are not well established. Heavy populations can do extensive damage, particularly on seedlings or young plants. Consider treating plants less than 12 weeks of age if aphids are present in numbers sufficient to cause stunting. Older plants can tolerate considerably more aphids and if heavy infestation occurs 3 to 4 weeks before harvest, harvest the field instead of spraying.