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Pea Aphids



North Central IPM Center

Pea Aphids

Hemiptera: Aphididae
Pulse Crops: Pea, lentil

Description

One of the most common insect pests found in pulse crops is the pea aphid. They are small, about 1/8+ inch long and pale to dark green with reddish eyes.

Life cycle

Pea aphids have multiple generations per year and overwinter as eggs in alfalfa, clover or vetch. In the spring, nymphs hatch from eggs and appear similar to the wingless adult but smaller. Nymphs molt four times and mature into adults in 10 to 14 days. Pea aphids can reproduce rapidly when temperatures are around 65F and relative humidity near 80 percent. Infestations can originate from local alfalfa fields or can migrate in from the southern states.

Damage

Aphids suck the sap from plants and may vector viral diseases. Populations of only ten aphids per plant can cause economic damage, especially if plants are heat stressed. Pulse crops are especially susceptible in the flowering and early pod stage can result in lower yields due to less seed formation and smaller seed size. Protein content and other quality issues do not appear to be affected by aphid feeding. Aphid populations are usually kept low by heavy rains or by beneficial insects (parasitoid wasps) and predators, such as lady bird beetle and lacewings. Early seeding also can reduce damage caused by pea aphids.

Pest Management

Scouting for aphids in pulse crops is conducted using either a sweep net or examining the number of aphids per plant tip when 50 to 75 percent of the crop is flowering. Take 180 degree sweeps using a 15-inch sweep net or check at least five 8-inch plant tips from four different locations in the field. Population estimates should be calculated by averaging counts taken from four separate areas of the field. Insecticides should be considered when the following action thresholds are reached:

Economic Thresholds

Economic thresholds may vary depending on the value of the crops and cost of control, as well as variation in potential seed weight caused by variation in precipitation and heat stress.

Peas

The economic threshold in peas at $5.71 per bushel and average control cost of $6.73-$9.25/acre is 2 to 3 aphids per 8-inch plant tips, or 9 to 12 aphids per sweep (or 90 to 120 aphids per 10 sweeps), at flowering. If the economic threshold is exceeded, a single application of insecticide when 50% of plants have produced some young pods will protect the crop against yield loss and be cost-effective. Cultivars of peas may also vary in their tolerance to feeding by pea aphids, thus economic injury levels may differ between cultivars. The economic thresholds presented above were developed using "Century" field peas.
The following table relates yield loss in peas for average aphid counts from 1 to 8 aphids per 8-inch pea stem tip when about 25% of the crop has begun to flower.

Research in Manitoba has shown that insecticides applied when pods first form protects pea yield better than earlier or later applications. Control at the early pod stage provides protection through the pod formation and elongation stages, which are very sensitive to aphid damage.

 
   
   
         
    Pea aphids adult & nymphs Pea aphids nymph - closeup
   

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