Peas (Pisum sativum) are hardy, cool-season annuals that grow in most climates. Depending on the cultivar you select, peas can be grown as sweet peas, snap peas, snow peas or garden peas. A healthy pea harvest depends on effectively controlling a common pest -- the pea aphid.
Pea aphids (Acyrthosiphon pisum, Macrosiphum spp.) are tiny, soft-bodied insects with light to dark green bodies. These pests thrive in dry, cool weather and populations can increase rapidly because the females give birth to live young without mating. Each female can produce up to 100 nymphs during her lifetime. Adults survive winters in mild climates by hiding in plant debris, but only unhatched eggs can survive cold-climate winters. Pea aphids typically gather in large groups on the undersides of leaves.
Like other aphids, pea aphids feed by piercing plant tissue and sucking out the juices. Feeding injuries show up as wilted or yellowed leaves and stunted plant growth. These aphids might also carry the pea enation mosaic virus, which causes mottled, curled and misshapen leaves.
Large numbers of aphids also produce an abundance of honeydew, a sweet, sticky substance that promotes the growth of sooty mold fungi. Although the sooty mold fungi themselves don't harm pea plants, the fungal colonies can grow so thick the plant can't photosynthesize. This can result in stunted growth, premature leaf drop and death of the plant. Rinse the sooty mold off your plants with water from a garden hose and prevent future fungal growth by controlling the pea aphids.
Start treating your pea plants with non-chemical control methods as soon as you spot any signs of aphids. Avoiding chemical treatments helps encourage populations of the pea aphids' natural enemies, including ladybugs, parasitic wasps, damsel bugs and lacewings.
Control small populations by spraying your plants with a strong blast of water from the garden hose. Clemson Cooperative Extension suggests using an aluminum foil mulch around plants to help repel the pests. Placing yellow containers full of water near peas might also attract and trap the pea aphids before they can harm your plants. Rake up all fallen plant material after harvest to prevent aphids from overwintering in your garden.
Use pesticides only when weather conditions don't support the presence of ladybugs and other natural predators, advises University of Illinois Extension. Insecticidal soap sprays can effectively treat large pea aphid populations.
Following the instructions and safety precautions on the product's label, mix 5 to 8 tablespoons of insecticidal soap into 1 gallon of water. Put it in a sprayer and spray the plants to cover the tops and undersides of the leaves. Insecticidal soap works only on contact. Spray the pea plants during the evening or early in the morning when honeybees and other beneficial insects are less likely to be present. Repeat applications every four to seven days until the pea aphids are gone.