Potato Aphid

The potato aphid has both a pink and a green color biotype. This aphid is much bigger than the green peach aphid with a more elongate body shape and is generally found on the terminals of tomato plants later in the season than green peach aphids. It is also considered to be more damaging.

High potato aphid populations can distort leaves and stems, stunt plants, and cause necrotic spots on leaves. These aphids also secrete a large amount of honeydew that promotes development of sooty mold on foliage and fruit. Plants are particularly susceptible to yield losses from high infestations during the period from 6 to 8 weeks before harvest. Yield losses from equally high aphid populations decline substantially as harvest approaches, unless aphid densities are reducing leaf area enough to permit sunburn.

Monitor potato aphids from 6 to 8 weeks before harvest as well as the level of parasitism and the activity level of predators. Treatments may be necessary if natural enemy activity is low and populations are increasing.

Naturally occurring parasites and predators of the potato aphid are common and can provide control. Monitor the proportion of aphid mummies relative to unparasitized aphids and the numbers of predators such as lady beetles, lacewing larvae, and syrphid larvae. If the proportion of mummies is increasing or predators appear to be gaining control and aphid populations are not yet damaging, avoid sprays that will disrupt these natural enemies.

There is considerable difference in tomato variety susceptibility to potato aphid feeding. Varieties containing the Mi gene, which confers resistance to nematodes, have been reported to be more tolerant of potato aphid infestations. However, this resistance no longer appears to be as effective as it once was, particularly against the pink form of the potato aphid.

The use of tolerant varieties, biological control, and sprays of herbal oils, pyrethrin, or insecticidal soap are acceptable for use on an organically certified crop. Repeated applications may be necessary for control.

1. Monitor potato aphids from bloom to early fruit set by picking the leaf below the highest open flower on 30 plants selected at random throughout the field.
2. Record on a monitoring form (PDF) the presence or absence of potato aphids on each leaf, while noting natural enemies.
3. Treat if 50 to 60% or more of the leaves are infested.
4. During late fruit set, combine monitoring for potato aphid with monitoring for tomato fruitworm:
   1. Pick the leaf below the highest open flower on 30 randomly selected plants from throughout the field.
   2. Record observations on a monitoring form (PDF).
   3. Consider a pesticide application. If 50% of these leaves are infested during the period 6 to 8 weeks before harvest, the resulting loss is about 1 ton per acre, and a pesticide application should be made.

Good spray coverage is important in controlling high populations. Ground sprays using hollow-cone nozzles or air-assist sprayers will provide the best canopy penetration. Higher spray volumes are also helpful.

• Photos of natural enemies of aphids
• Potato aphid monitoring form (PDF)
• Potato aphid and fruitworm monitoring form (PDF)