Aphids Pests of Vegetables

August 2017
Cami Cannon & Bonnie Bunn, Vegetable IPM Associates • Marion Murray, Extension IPM Specialist • Diane Alston Extension Entomologist • Erin Petrizzo, Research/Extension Assistant

aphid live birth
Fig. 1. A green peach aphid giving birth to live young (vivipary).
aphids on tomatoFig. 2. A tomato infested with aphids. When aphids molt, white "skins" are left behind.
winged green peach aphidFig. 3. Winged form of an adult green peach aphid.
green peach aphid
Fig. 4. Green peach aphid (Myzus persicae)
potato aphid
Fig. 5. Potato aphid (Macrosiphum euphorbiae)
melon aphids
Fig. 6. Melon aphids (Aphis gossypii)
cabbage aphids
Fig. 7. Cabbage aphids (Brevicoryne brassicae)
aphid feeding injury
Fig. 9. Aphid infestations can cause leaves to curl (top lefT) and/or become yellow (top right). Aphids also feed on stems (boom left) and fruit (bottom right).
aphid feeding
Fig. 11. In non-persistent transmission, aphids need only very short feeding times (usually fom tissues near the surface of leaves) to obtain the virus on their mouthparts.
viruses caused by aphids
Fig. 12. Mosaic virus symptoms on a pumpkin leaf (left). Mosaic virus symptoms can also occur on fruits, such as squash (right).
lady beetles
Fig. 13. Lady beetle adults often lay eggs (left) near aphids so that larvae (right) will have food available when they hatch.
aphid predators
Fig. 14. Aphid predators include: damsel bug (top left), syrphid fly larva (top right), predatory midge (bottom left), and lacewing larva (bottom right).
parasitic wasp
Fig. 15. Parasitic wasps parasitize aphid bodies turning them dark in color (upper left); a wasp pupates within the aphid body, turning it into an enlarged mummy (upper right); and a new adult wasp emerges from the aphid leaving an exit hole in the hold aphid body (bottom).
sick aphid
Fig. 16. This color-aphid has been infected and killed by the entomopathogenic fungus Beauveria bassiana.

Quick Facts

  • Aphids are small, soft-bodied insects that suck sap from plant tissues.
  • Aphid feeding distorts and stunts plants, produces honeydew that supports sooty mold fungi, and can vector plant viruses.
  • During spring and summer, aphids can be abundant.
  • One of the most serious problems caused by aphids to vegetable crops is the spread of plant viruses.
  • Biological control from predators and parasitoids is a key contributor to suppressing aphid populations.
  • Insecticidal soap or horticultural oil sprays can reduce aphid populations and conserve natural enemies.

Aphids are a diverse family of insects with many species that inflict similar plant damage, and can be managed using similar tactics. This fact sheet will focus on four of the most common aphids that are pests of vegetable crops in Utah:
Green Peach Aphid (Myzus persicae)
Potato Aphid (Macrosiphum euphorbiae)
Melon Aphid (Aphis gossypii)
Cabbage Aphid (Brevicoryne brassicae)

Description

Aphids are small, soft-bodied, pear-shaped insects with two tailpipe-like appendages called “cornicles.” Cornicles are unique to aphids, and excrete defensive compounds (waxes and alarm pheromones).
Aphids vary in color, including within species, depending on maturity, food source, genetic lineage, and their environment. Juvenile aphids (nymphs) look like adults, except smaller in size (Fig. 1). As nymphs feed and grow they molt, casting off white skins (exoskeleton) that can be seen near the colony (Fig 2). Nymphs develop through about four molts before becoming adults.
Adult aphids can be winged or wingless (apterous). Winged forms generally have slimmer bodies and transparent wings. The winged form of the green peach aphid has dark spots on its green body (Fig. 3).

Green Peach Aphid

Description: Yellow to green in summer; vary from pale to dark-green, pink, or red in fall. Range in length from 0.06 to 0.09 in (1.5 to 2.3 mm).
Plant Hosts: Fall - Spring: peach, apricot, nectarine
Summer: vegetables - tomato, potato, pepper, eggplant, squash, pumpkin, cucumber, spinach, mustards, cabbage, broccoli, legumes, celery, okra, corn; other crops - tobacco, canola, sunflower, other flowers; and weeds - lambsquarters, common tumbleweed, nightshade, sowthistle, mustards, many others

Potato Aphid

Description: Pink or green; 0.07 to 0.16 in (1.8 to 4.1 mm) long.
Plant Hosts: Fall - Spring: wild and ornamental rose
Summer: vegetables & fruit - potato, tomato, eggplant, sunflower, pepper, pea, bean, apple, turnip, corn, sweet potato, asparagus; and weeds - ragweed, lambsquarters, jimsonweed, pigweed, shepherd’s purse, wild lettuce, clover

Melon Aphid

Description: Mottled light and dark green or almost black; however, yellow forms do occur. Average 0.06 in (1.5 mm) long.
Plant Hosts: Fall - Spring: catalpa, rose of Sharon
Summer: vegetables - cantaloupe, honeydew, casaba, Persian melon, watermelon, cucumber, squash, pepper, asparagus, eggplant, okra; other crops - cotton, citrus; and weeds - milkweed, jimsonweed, pigweed, plantain, field bindweed

Cabbage Aphid

Description: Gray to green with a grayish waxy covering and short cornicles. About 0.07 to 0.1 in (1.8 to 2.5 mm) long.
Plant Hosts: Fall – Spring: cole crop residue, weeds
Summer: vegetables - broccoli, cauliflower, cabbage, Brussels sprouts, kale, collards, kohlrabi, oilseed rape, Chinese broccoli, Chinese cabbage, radish, kale; and weeds - Indian mustard, white mustard, black mustard

Life Cycle

The life cycle of aphids can be complex, and differs among species. A generalized description is shown in Fig. 8.

Green peach, potato, and melon aphids require a woody host to complete their life cycle. They overwinter as eggs on woody hosts and hatch in spring, producing only females. These spring aphids feed on the succulent new growth, and when mature, give birth asexually (parthenogenesis) to live female offspring. As the weather warms (70-81°F is optimal), aphids can complete a generation in as little as 7-8 days. Females can produce up to 12 nymphs per day for 50-100 total offspring. After 2-6 generations on the woody hosts, the aphids form wings and migrate to vegetable crops and other hosts for the summer, where they complete many more generations. As temperatures cool in the fall, aphids again form winged offspring (male and female) and return to winter host plants, where sexual mating occurs and eggs are laid for overwintering.

Cabbage aphids do not require an alternation of host plants. In northern Utah, they overwinter as eggs on crop debris, and in southern Utah, they may overwinter as adults. In spring, eggs hatch to all females, and reproduction occurs as noted above on mustard family plants. Winged aphids form when colonies become too crowded, resulting in dispersal to other brassica hosts. Cool fall temperatures cause sexual mating and egg-laying for overwintering.

Aphid Life Cycle
Fig. 8. Generalized aphid life cycle in Utah. Many species of aphids live on a woody host from fall to spring, and migrate to vegetables or weeds for the growing season.

Injury

Aphids feed on buds, leaves, flowers, stems, and fruits with piercing-sucking mouthparts. Feeding causes plant structures to become stunted, yellowed, and distorted. Curled leaves create a micro-environment that protects aphids from predators, insecticides, and the environment (Fig. 9).

Aphid feeding results in an overall loss of plant vigor. Early in the season, young vegetable plants can suffer loss of productivity and reduced plant health. Cabbage aphids can cause significant economic losses due to contamination of produce. In broccoli, they feed within the flower stalks, and in Brussels sprouts, they feed within the developing heads.

Aphids excrete a sugary substance called honeydew which can cover plant surfaces and harm crop quality and marketability. Sooty mold fungi may grow on the honeydew, blocking sunlight and reducing plant vigor. Honeydew attracts ants, which can protect aphids by warding off predators to protect their honeydew food source.

Aphid-Vectored Plant Viruses

One of the most serious problems caused by aphids to vegetable crops is the spread of plant viruses. Viruses can dramatically reduce crop yield, and even kill plants. All four of the aphids discussed here can transmit viruses to vegetable crops. The green peach aphid is known to transmit more than 100 different viruses.

Winged aphids can spread viruses from infected to healthy plants. Even when aphid numbers are below detectable levels, there is still a risk of virus introduction from virus-infected aphids immigrating into a field. Utah’s most common aphid-vectored viruses are nonpersistent, meaning, they do not survive and replicate within the insect. After an aphid obtains virus particles on its mouthpart from an infected plant, it can transmit the virus to an uninfected plant only once. The feeding process must be repeated for further spread. (Fig. 11).

Vegetables Susceptible to Aphid-Transmitted Viruses
beans
beets
bok choy
broccoli
Brussels sprouts
cabbage
cauliflower
chard
cucumber
kohlrabi
lettuce
melon
pepper
potato
pumpkin
squash
tobacco
tomato

Common Aphid-Vectored Vegetable Viruses

There are numerous plant viruses, and plants can be infected with more than one type of virus. Viruses are typically named for the first host plant on which they were described; however, most viruses can infect more than one plant species. Some viruses also infect weeds.

Some virus symptoms mimic those of other problems; diagnostic tests are typically required to confirm a virus infection. The mosaic viruses, however, cause unique symptoms that can be visually identified. Although there are many types of mosaic viruses, most cause mottled shading of green and yellow or other colors, on leaves and fruit (Fig. 12).

Name Common Vegetable Hosts
(Detetected in Utah)
Common Vegetable Hosts
(Other Potential Hosts)
Symptoms
Alfalfa Mosaic Virus tomato, pepper, potato, pea, bean   Bright yellow blotches with some mottling, turning to a bronze discoloration on leaves; necrotic phloem tissues; necrotic rings and spots on fruit; sometimes solid brown necrosis on surface of fruit; plant death
Cucumber Mosaic Virus cucurbits tomato, pepper, bean, lettuce, spinach, carrot, celery, beet Symptoms vary with the host, mottling on leaves and fruit; sometimes severely stunted plants
Potato Virus Y potato tomato, pepper Symptoms will vary among potato cultivars, mild to severe mosaic or mottling on leaves; sometimes leaf drop; stunted plants; necrotic or dead rings on tuber skin
Watermelon Mosaic Virus cucurbits pea Strong mosaic on foliage; leaf distortion and deep leaf serration; malformed fruit with knobby bumps; host range is not limited to cucurbits and may overwinter in leguminous species such as clover

Management of Viruses

Plants cannot be cured of virus infections; thus, prevention and reduction of spread are the most effective management practices. While predators play an important role in reducing aphid populations, their action is too slow to prevent the transmission of most viruses.

  • Remove and destroy infected plants. Migrating aphids can spread non-persistent viruses rapidly, which makes controlling the spread of viruses with insecticides ineffective. A better management tactic is to eliminate plant sources of viruses, including weeds. Once vegetable harvest is complete, use effective field sanitation practices such as removal and disking under of crop debris.
  • Plant resistant cultivars. If virus infection has been a problem in the past, check to see if there are resistant cultivars available.
  • Plant early. Crops planted late in the season tend to be more susceptible to viral diseases because they are young during peak virus infection and spread periods. Planting early may decrease virus symptom intensity. If planting early isn’t an option, avoid planting next to crops that are also susceptible to the virus since these crops may be a virus source.
  • Use reflective mulches. The use of reflective or aluminum mulches early in the season has been found to repel migratory aphids from young plants; thus, reducing the spread of viruses.
  • Use vegetable or mineral oil sprays. Viral transmission may be reduced by coating foliage with vegetable or mineral oil (in crops not damaged by oil sprays). The oil coats the mouthparts (stylets) of feeding aphids and interferes with virus transmission. The use of oil sprays is most effective when disease and aphid populations are low, and temperatures are below 90°F.

Management of Aphids

Monitoring

  • Scout frequently. Since aphid colonies can quickly increase, it is important to scout plants at least twice weekly when plants are young and growing rapidly. Look on the underside of leaves where aphids congregate, and look for ant activity. Once aphid feeding causes leaf curling, it is more difficult to reduce aphid numbers. Most species of aphids cause the greatest damage when temperatures are warm, but not hot (65° to 80°F).
  • Use yellow sticky traps to monitor aphid populations. Yellow sticky cards will attract winged aphids. Online vendors of sticky cards include Great Lakes IPM, Grow Organic, Gempler’s, Trécé, and Alpha Scents.
  • Thoroughly scout fields and nearby crops and weeds. Aphid infestations typically begin as scattered colonies within a field. Therefore, it is important to monitor all sections of a field and nearby crops and weeds that may serve as aphid sources. Aphid “hot spots” can be managed by removing infested plants or treating the infested area with insecticides

Cultural and Mechanical Control

  • Use preventive measures. Before planting, remove weeds and volunteer crops that can serve as aphid hosts.
  • Encourage natural enemies. Plant strips of yarrow, alyssum, herbs and other plants with small, attractive flowers that provide nectar and pollen for beneficial insects.
  • Inspect transplants for aphids before planting; dispose of infested plants.
  • Manage nitrogen levels. High levels of nitrogen fertilizers tend to encourage aphid reproduction. Use several, staggered applications of lower concentrations of nitrogen rather than a single high dose. Also, use delayed-release formulations.
    Use row covers. Row covers put in place at planting through start of bloom can exclude melon aphids in cucurbit crops.
  • Use reflective mulches. Reflective silver or aluminum mulches can repel winged aphids.

Biological Control

Conservation and attraction of native natural enemies is one of the most effective means to prevent aphid outbreaks. In some situations, such as within greenhouse tunnels, purchasing and releasing biocontrol agents for aphid management can be of value. Some suppliers of beneficial organisms include Arbico Organics, Biocontrol Network, Do My Own Pest Control, and Rincon-Vitova Insectaries. Generalist predators not only control aphid populations, but also feed on other pests such as thrips, leafhoppers, and mites. Low levels of aphids in the environment are desirable in order to maintain healthy populations of beneficial insects. The most well-known aphid predators include lady beetles (Fig. 13), lacewings, and syrphid flies. Others include soldier beetle, minute pirate bug, damsel bug, and predatory midges (Fig. 14).
Aphids may also fall victim to insect fungal diseases under humid conditions leaving them off-color, bloated, or flattened (Fig. 16). Adequate populations of natural enemies can suppress aphid infestations without the need for insecticide treatment. There is typically a delay in the increase of natural enemies following a rise in aphid populations; however, provision of attractive flowers to provide nectar and pollen, and avoidance of toxic insecticides are the key factors in encouraging aphid biological control.

Chemical Control

General action thresholds to determine whether and when to treat for aphids in vegetable crops include:

  • When plants are young, aphid populations are increasing, and aphids occur on 50-60 % of the leaves.
  • When aphid populations remain at 8 to 10 or more per leaf for two or more consecutive weeks.

Cabbage aphid thresholds:

  • Cabbage, broccoli, and cauliflower: treat as soon as 1 to 2% of plants are infested with one or more aphids and after treating, continue checking fields and treat if populations reappear.
  • Brussels sprouts: treat when 15% of plants are infested (this is conservative). Brussels sprouts can tolerate 40% infested plants from transplanting up until 2 weeks before harvest.

Only use insecticide applications when needed. Rotate among different insecticide classes between applications as aphids are prone to developing resistance. This has already occurred with pyrethroids for populations of green peach aphid and melon aphid in agriculturallyintensive areas of the U.S. Select insecticides with the least harmful effects to beneficial insects, and high selectivity for the target pest.

Botanigard is a biological insecticide for commercial growers labeled for control of aphids. The active ingredient, Beauveria bassiana, is an entomopathogenic fungus that causes the white muscadine disease in aphids and other insects.

Insecticidal soap and horticultural oils (discussed below) are good options to treat aphids before populations increase to high levels. Thorough spray coverage is important for good aphid control. It can be difficult to reach aphids on the underside of leaves or in curled leaves. Ground sprays using hollow-cone nozzles or airassist sprayers will provide the best canopy penetration. Higher spray volumes are also helpful.

Organic: Organically approved insecticides include insecticidal soap and oils (petroleum, mineral, canola, clove, garlic, rosemary, and neem). Oil and soap sprays kill aphids on contact by physical means (suffocation and disruption of waxes in the exterior cuticle), so thorough coverage is essential for good efficacy. These products also kill beneficial insects in the same way, but there is no residual activity, so natural enemies that arrive post-spray are unharmed. Beneficial insects are most active during the day, so the best time to spray is early in the morning, late afternoon, or at or after dusk.
Caution: Do not use soap or oils on water-stressed plants or when temperatures will exceed 90°F within 4 hours of application. These materials may be phytotoxic to some plants, so always check the label. If unsure about phytotoxicity, test the spray on a few plants before treating an entire field.
Additional certified organic products include pyrethrins, and other botanical and microbial insecticides.

Conventional: Keep in mind that some conventional insecticides also kill beneficial insects that help keep aphids and other pests under control. If a conventional product is necessary, recommended active ingredients include acetamiprid, bifenthrin, cyfluthrin, imidacloprid, and malathion.
Caution: Some insecticides are labeled for use against aphids but should not be used on food crops. Always check product labels for registered uses.

Commercial growers may reference the Utah Vegetable Production & Pest Management website for spray options.

Examples of home use insecticides registered in Utah that are effective for aphid contorl on vegetables.
Active Ingredient  Brand Name MoA* Residual (days)
malathion Hi Yield, Spectracide Malathion, Ortho Malathion 1B 7
bifenthrin Fertilome Broad Spectrum Insecticide, Bonide Eight Insect Control, Ortho Bug-B-Gon Max Lawn and Garden Insect Killer 3 14
cyfluthrin BioAdvance Vegetable and Garden Insect Spray  3 14
deltamethrin Green Light Many Purpose Dust  3 14
esfenvalerate Monterey Bug Buster II 3 ---
gamma-cyhalothrin BioAdvance Complete Insect Dust, Lily Miller Multi-Purpose Insect Spray 3 14
pyrethrins Monterey Bug Buster-OOB 3 5
pyrethrins + canola oil Earth-tone Insect Control, Monterey Take Down Garden Spray 3/UN 5
pyrethrins + piperonyl butoxide Bonide Pyrethrin Garden Insect SprayB, Garden Tech Worry-Free Insecticide and MiticideB 3 3
pyrethrins + potassium salts of fatty acids (insecticidal soap) Safer Tomato & Vegetable Insect KillerO, Safer Yard & Garden Insect KillerO 3/UN 5
pyrethrins + sulfur Bonide Tomato and Vegetable 3 in 1, Natria Insect Disease & Mite ControlB, Ortho Insect Mite & Disease 3 in 1 3/UN 5
acetamiprid Ortho Flower Fruit & Vegetable 4A 14
capsaicin and related capsaicinoids Bonide Hot Pepper Wax Insect Repellent NC ---
oil: canola, neem, rosemary, clove, cottonseed Natria Multi-Insect ControlOB, Monterey All Natural 3 in 1 Garden Insect Spray physical 1
potassium salts of fatty acids (insecticidal soap) Natria Insecticidal Soap, Safer Insecticidal SoapOB physical 1

*Mode of Action (MoA) is a classification number based on guidelines from the Insecticide Resistance Action Committee. Rotate among insecticide classes to reduce the development of resistance.
O Organically certified insecticide products.
B Biological pesticide
NC Not Classified

References and Further Reading

Image Credits

2 J. Obermeyer, Purdue Extension Entomology
3 Scott Bauer, USDA Agricultural Research Service, Bugwood.org
4 David Cappaert, Michigan State University, Bugwood. org
5 Joseph Berger, Bugwood.org
6 Mississippi State University Archive, Mississippi State University, Bugwood.org
7 Alton N. Sparks, Jr., University of Georgia, Bugwood.org
14 Syrphid fly larva: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org; Predatory midge: Whitney Cranshaw, Colorado State University, Bugwood.org; Lacewing larva: Joseph Berger, Bugwood.org  

15 Parasitized aphids (left): Patrick Porter, Texas Cooperative Extension, Bugwood.org; Aphid mummies (right): Alton N. Sparks, Jr., University of Georgia, Bugwood.org; Emerged Wasp (bottom): Jack Kelly Clark, Communication Services and Information Technology
16 Whitney Cranshaw, Colorado State University, Bugwood.org

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