Controlling aphids in your garden

Aphids are small, soft-bodied insects that suck sap from plant tissues and act as vectors for viruses that can infect the plant. Aphids feed on buds, leaves, flowers, stems and fruits with their piercing, sucking mouth parts. The leaves become stunted, yellow, and distorted. The curled leaves protect the aphids from predator insects. Overall plant vigor and productivity is reduced, causing economic losses for the producer.

There are several species of aphids that can damage vegetable plants in Idaho. The Green Peach Aphid (Myzus persicae), the Potato Aphid (Acrosiphum euphorbiae), the Melon Aphid (Aphis gossypii) and the Cabbage Aphid (Brevicoryne brassicae).

Green Peach Aphids (Myzus persicae), Potato Aphids (Acrosiphum euphorbiae), Melon Aphids (Aphis gossypii)

Green peach aphids are yellow to green in color during the summer. During the fall they vary from pale to dark-green, pink, or red. They vary in size from 0.06 to 0.09 inches in length. During the fall, they prepare for winter and infect woody plants like peach, apricot and nectarine trees.

During the summer they infect tomatoes, potatoes, peppers, eggplant, squash, pumpkin, cucumber, spinach, mustards, cabbage, broccoli, legumes, celery, okra and corn. They also can infect ornamental plants and weed species. Because they need a woody plant to complete their life cycle, in potato seed management areas like northern Fremont County, growing peach, apricot and nectarine trees is not allowed.

Potato aphids are pink or green. They vary in size from 0.07 to 0.16 inches long. They overwinter on wild and ornamental roses. Summer vegetables infected include potatoes, tomatoes, eggplant, sunflower, pepper, pea, bean, apple, turnip, corn, sweet potato and asparagus. They also infect several weed species.

Melon aphids are mottled light and dark green or almost black; however, yellow forms do occur. They average 0.06 inches long. They overwinter on catalpa and rose of Sharon. Vegetables infected include cantaloupe, honeydew, cucumber, squash, pepper, asparagus, eggplant, and okra. They also infect several weed species.

These three groups of aphids do best in temperatures of 70-81°F and can complete a generation in as little as 7 to 8 days. Females can produce up to 12 nymphs per day for a total of 50 to 100 offspring. After two to six generations on the woody hosts, the aphids form wings and migrate to vegetable crops and other host for the summer, where they complete many more generations. When the temperature starts to fall, they return to the woody plants where they lay eggs that will overwinter.

Cabbage Aphid (Brevicoryne brassicae)

Cabbage aphids are gray to green with a grayish waxy covering and short cornicles. They vary from 0.07 to 0.1 inch long. In the fall and spring, they infect cole crop residue and weeds. During the summer they infect broccoli, cauliflower, cabbage, Brussel sprouts, kale, collards, kohlrabi, oilseed rape, Chinese broccoli, Chinese cabbage, radish, and kale. They also infect several weed species.

Cabbage aphids do not need multiple host plants. They can overwinter in leaf litter. When a colony becomes too crowded, adults form wings and disperse to other plants. Cooling temperatures encourage sexual reproduction and egg-laying for overwintering.

Viruses

The most impactful damage from aphids is done through the transmission of viruses. Susceptible vegetables include beans, beets, Bok choy, broccoli, Brussels sprouts, cabbage, cauliflower, chard, cucumber, kohlrabi, lettuce, melon, pepper, potato, pumpkin, squash and tomato.

Common viruses spread through aphids include Alfalfa Mosaic Virus, Cucumber Mosaic Virus, Potato Virus Y and Watermelon Mosaic Virus. Plants cannot be cured of virus infections, so prevention is essential. Some things you can do are to remove and destroy infected plants, plant resistant cultivars, plant early, use reflective mulches, and use vegetable or mineral oil sprays.

Management of Aphids

Monitoring is important to prevent large infestations. The more quickly you can identify the problem, the more effective you can be in reducing the damage. Use yellow sticky traps to monitor aphid populations.

Use preventative measures like removing any weeds or volunteer crops that can serve as aphid hosts. Encourage natural enemies, there is a variety of predatory insects that feed on aphids. Encouraging insects like the Syrphid fly, green lacewings, and ladybugs can naturally reduce aphid populations.

Staggering nitrogen applications throughout the growing season will help as high levels of nitrogen fertilizers encourage aphid reproduction.

Reflective mulch like reflective aluminum can repel winged aphids.

If you have aphids on your plants using a strong spray of water will wash them off the plants. This is preferred over using chemicals, as the chemicals may affect the desirable predatory insects that feed on the aphids.

Chemical control should be used when aphids occur on more than 50% of the leaves or when there are 8 to 10 or more per leave for two or more consecutive weeks. Several options for chemical control are available to non-licensed pesticide applicators.

For more information on available chemicals visit this site. Always read and follow the label directions.