Aphids, also known as plant lice are soft-bodied, sucking insects. They feed on plant sap and excrete a sugary honeydew that attracts ants and creates the conditions for sooty mold, a type of fungus (saprophytic) that feeds on decaying organic matter.
There are several aphid species, all belonging to the insect family Aphididae, that are capable of attacking any type of vegetation. Aphids that pose the most serious problem to Wisconsin vegetable production include the green peach, melon, and potato aphids.
All aphids are soft-bodied and pear-shaped with a pair of cornicles, or little horns, projecting from the rear end of their abdomens. Adult aphids may or may not be winged. Some of the more common species are listed below.
Table 1. Common Wisconsin aphid species
|Common name||Scientific name||Description||Host plants|
|Asparagus aphid||Brachycorynella asparagi||Small, bluish-gray in color, powdery||Asparagus|
|Bean aphid||Aphis fabae||Dark green to sooty black||Artichoke, asparagus, bean, carrot, corn, lettuce, parsnip, rhubarb, spinach, squash|
|Cabbage aphid||Brevicoryne brassicae||Gray-green with a powdery, waxy covering||Broccoli, Brussels sprouts, cabbage, collards, kale, kohlrabi, and radish|
|Corn leaf aphid||Rhopalosiphum maidis||Bluish-green||Corn|
|Green peach aphid||Myzus persicae||Yellowish-green with 3 dark lines on their backs||Beet, celery, cole crops, cucurbits, lettuce, pepper, potato, spinach, tomato|
|Melon aphid||Aphis gossypii||Pale yellow to brown or nearly black with black cornicles||Asparagus, bean, beet, celery, cucurbits, okra, spinach|
|Pea aphid||Acyrthosiphon pisum||Pale green with black legs||Peas|
|Potato aphid||Macrosiphum euphorbiae||Pink to green in color, relatively large||Potato, tomato, eggplant, sunflower, peppers, peas, beans, apple, turnip, corn, sweet potato, asparagus, clover, roses|
Symptoms and effects
Reduced plant vigor, stunting and deformed plant parts are common symptoms of aphid infestations. In some cases, it’s the production of honeydew or presence of sooty mold that alerts the gardener to an aphid outbreak. Most importantly, aphids are excellent transmitters of several viral diseases, such as the mosaic viruses, that cause leaves to shrivel and that infect a wide range of hosts. In some cases, it’s the appearance of virus symptoms that indicate aphid activity.
It is difficult to generalize the life cycle of all aphids because of the diversity of their life habits, which can range from single to multiple hosts. One of the unique characteristics of aphids that sets them apart from all other insects is their ability to bear live young. Aphids overwinter as eggs on a perennial host. In spring, the eggs hatch and the aphids migrate onto their summer host when it becomes available. The female aphids can then reproduce without mating and will hold the eggs in their bodies to give birth to live young. By eliminating mating and egg laying, aphids have successfully shortened their life cycle and thereby increased their reproductive capability. Throughout the summer, wingless females predominate. However, winged forms may arise when populations become too large for the available food source. In late summer, in response to the shortened daylight hours, wingless females and males are produced for the purpose of mating and laying fertilized eggs that will survive adverse winter conditions.
Look for “hot spots” of aphid activity scattered throughout the field. Because of the spotty nature of infestations, look for aphids on a number of plants in several areas. Examine the terminals of 15 consecutive plants or sample units and rate the plants as infested or uninfested. Given the huge reproductive potential of aphids, an infestation level of 5%-10% indicates a potentially damaging infestation. Repeat checks at weekly intervals to determine the need to treat.
Predators such as lady-bird beetle adults and larvae, green lacewing larvae, syrphid fly larvae and several parasitic wasps all help reduce aphid numbers. Heavy rains help dislodge aphids from the plant and, during periods of high humidity, fungal diseases may greatly reduce populations. The remarkable reproductive capacity of the aphid normally overcomes the effects of natural controls in spring when cool temperatures hinder the development of natural enemies. These natural controls most often catch up in the warmer weather of summer and fall.
Treat crops with an insecticide when threshold levels have been reached. One of the problems associated with the control of green peach and melon aphids results from their resistance to several insecticides. In particular, aphids have shown resistance to organophosphate insecticides.
Refer to the UW-Extension publication Commercial Vegetable Production in Wisconsin (A3422) for a list of registered insecticides and management recommendations.
Asparagus aphid (Brachycorynella asparagi)
Appearance:Small, bluish-gray in color, powdery, with small cornicles
Host plant: Asparagus
Description: The asparagus aphid is a recent import from Europe that causes a brooming distorted growth of the ferns of asparagus. It is bluish gray in color, and the cornicles aren’t readily apparent. Normally only isolated plants are affected and can be spot treated.
Bean aphid (Aphis fabae)
Appearance: Dark green to sooty black
Host plants: Artichoke, asparagus, bean carrot, corn, lettuce, parsnip, rhubarb, spinach, squash
Cabbage aphid (Brevicoryne brassicae)
Appearance: Gray-green with a powdery, waxy covering
Host plants: Broccoli, Brusssels sprouts, cabbage, collards, kale, kohlrabi, radish
Overwinters as eggs on host plants
Corn leaf aphid (Rhopalosiphum maidis)
Appearance: Bluish green
Host plant: Corn
No winter host. Migrates from the south annually
Green peach aphid (Myzus persicae)
Appearance: Yellowish-green with 3 dark lines on their backs
Host plants: Beet, celery, cole crops, cucurbits, lettuce, pepper, potato, spinach, tomato
Winter hosts: Cherry and peach
Description: The green peach aphid is the most destructive and insecticide-resistant aphid in Wisconsin. Many crops are attacked including greenhouse transplants of pepper, tomato, and cabbage, along with beet, carrot, broccoli, Brussels sprouts, lettuce, eggplant, and potato. Green peach aphids are 1/8 inch long, yellowish green, peach, or dirty red in color, and can be found on the undersides of leaves. This aphid is a very efficient vector of many virus diseases. Scouting is usually done by examining the undersides of leaves and looking for aphid activity.
In potatoes, remove 25 leaves per sample from the lower half of 25 different plants, with at least 10 sample sites per field. Treat if more than 10 aphids are found per 100 leaves in seed fields or more than 30 per 100 leaves in table stock or processing potatoes.
Melon aphid (Aphis gossypii)
Appearance: Pale yellow to brown or nearly black with black cornicles
Host plants: Asparagus, bean, beet, celery, cucurbits, okra, spinach
Winter hosts: Many
Description: Melon aphid is a small dark aphid that can be found building up on the undersides of leaves of cucumber, squash, pumpkin, and melon. They can produce up to 10 generations per year and cause infested plants to yellow and wilt. Low numbers are most often controlled by natural enemies.
Pea aphid (Acyrthosiphon pisum)
Appearance: Pale green with black legs
Host plant: Peas
Winter host: Alfalfa
Potato aphid (Macrosiphum euphoribae)
Appearance: Relatively large, pink to green in color, with long slender cornicles
Host plants: Potato, tomato, eggplant, sunflower, peppers, peas, beans, apple, turnip, corn, sweet potato, asparagus, clover, roses
Overwinter as eggs on perennial host plants
Description: Potato aphids are larger than green peach aphids and come in both red and green. They attack eggplant, tomato, and potato and are most often found on young, actively growing tissue. To sample for potato aphids, remove leaves from the terminal parts of 35 plants and count the number of aphids. Repeat in at least 10 locations per field. When aphid counts exceed 20 per 100 in seed potato and 50 per 100 leaves in table or processing potatoes, control measures are suggested.
UW-Extension fact sheets
- Commercial Vegetable Production in Wisconsin (A3422)
- Biological Control of Insects and Mites (A3842)
- Biological Control of Greenhouse Pests (NCR58)
- Managing Insects in the Home Vegetable Garden (A2088)
- Aphids – Wikipedia