Bean & Southern Pea Insect Pests

Revised by Joey Williamson, HGIC Horticulture Extension Agent 02/14. Originally prepared by Randall P. Griffin, Extension Entomologist (Emeritus), Clemson University. Revised by Joey Williamson, HGIC Horticulture Extension Agent. (New 02/99, Rev. 08/09. Images added 05/09.)

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Major Seedling Feeders

Aphids: Aphids (Aphis species and Macrosiphum euphorbiae) are soft-bodied “plant lice,” about 1/16 to 1/8 inch in length and are usually green although some species are yellow, pink, brown or black. They are most prevalent during cool, dry weather on small plants. Heavy populations of aphids can stunt plants by withdrawing large volumes of plant juices and delaying maturity.

Severe cowpea aphid (Aphis craccivora) infestation.
Severe cowpea aphid (Aphis craccivora) infestation.
Clemson University - USDA Cooperative Extension Slide Series, www.insectimages.org

Treatments for aphid control should begin at any time colonies are found. In the home garden, spray foliage with soapy water, then rinse with clear water or use insecticidal soaps. Planting in aluminum foil that has been laid on the planting bed and filling yellow pans with water to trap the aphids are also effective control measures. Once the weather warms up, natural enemies usually control aphids.

Thrips: Thrips (Frankliniella species) are small, slender, agile insects, rarely as long as 1/8 inch. They are commonly found in flowers of peas and beans but will also feed on leaves. Their presence in flowers at early bloom may result in poor fruit set due to pollination interference by thrips feeding.

Western flower thrips (Frankliniella occidentalis) damage to bean leaf.
Western flower thrips (Frankliniella occidentalis) damage to bean leaf.
Whitney Cranshaw, Colorado State University, www.insectimages.org

Western flower thrips adult (Frankliniella occidentalis).
Western flower thrips adult (Frankliniella occidentalis).
Frank Peairs, Colorado State University, www.insectimages.org

Field observations indicate that three thrips per flower may interfere with pollination and cause defectively shaped pods. After pods are 1 to 2 inches long, damage is primarily cosmetic since small blisters are generally the only results of their feeding.

In the home garden, planting in aluminum foil that has been laid on the bed tends to repel thrips. Insecticidal soaps may give adequate control.

Lesser Cornstalk Borer: The lesser cornstalk borer (Elasmopalpus lignosellus) is the larval (immature) stage of a small (½ inch long) brownish-yellow moth. Moths leave field corn when it begins to dry and enter late-planted fields of peas and beans. The moths lay eggs around the base of emerging plants. These eggs quickly hatch into larvae, which are small, slender caterpillars with green, blue or brown bands around each body segment. The larvae bore into the stalks of young plants near the soil line and tunnel up and down the stalks. A silken tube is usually attached to the entrance hole where the larvae bore into the stem and the larva may sometimes be found in this tube. Plants damaged by lessers become stunted, wither and later die. Late plantings (those made after July 1) on sandy soil during hot, dry conditions often result in 30 to 50 percent stand loss.

Lesser corn stalk borer larvae (Elasmopalpus lignosellus) and damage to stem.
Lesser corn stalk borer larvae (Elasmopalpus lignosellus) and damage to stem.
Riley, University of Georgia, www.insectimages.org

Major Foliage/Stem Feeders

Several kinds of beetles and caterpillars may be found feeding on the foliage of peas and beans. The combined feeding of all or heavy populations of one species may require insecticide treatments. Peas and beans are fast-growing plants with heavy canopy due to an overabundance of leaves. Research has shown that 30 percent leaf loss prior to bloom stage will not result in reduced yield or quality. In addition, these plants can tolerate up to 15 percent leaf loss during bloom and pod-fill stages without significant drops in yield or quality.

The following pests are considered major foliage feeders and their combined feeding may require treatments to prevent yield and quality loss.

Mexican Bean Beetle: The Mexican bean beetle (Epilachna varivestis) is ¼ to ⅓ inch long, very convex and yellow to coppery-brown in color. Each wing cover has eight small, black spots that form three rows across the body. Some of the beetles appear at emergence of earliest plantings whereas others may wait until nearly two months later to leave their overwintering quarters.

Eggs, larvae and adult Mexican bean beetles (Epilachna varivestis).
Eggs, larvae and adult Mexican bean beetles (Epilachna varivestis).
Clemson University - USDA Cooperative Extension Slide Series, www.insectimages.org

After feeding on beans a week or two, the adult female deposits yellow eggs in groups of 20 to 50 on the undersides of leaves. The eggs hatch in one to two weeks, depending on temperature, and the larvae (immature forms) feed for two to four weeks. Both larvae and adults feed on the undersides of leaves, leaving the upper surface more or less intact. The larvae consume regular areas of leaf tissue leaving veins between the chewed areas, which give the leaf a skeletonized, lacy appearance. When abundant, larvae and adults will also feed on stems and pods. When full-grown, larvae are 1/3 inch long, yellow and armed with black-tipped spines. Larvae change to pupae (nonfeeding stage where the larvae change to adults) on plants — usually on the undersides of undamaged leaves. The pupal stage is cemented to leaves and emerges as an adult in about 10 days. From egg to adult requires about one month and there are usually three generations per year. During some years there may be a partial fourth generation.

Since most damage occurs during July and August, quick-maturing varieties of green beans planted very early or during late summer may escape damage. The snap bean varieties: ‘Wade’ and ‘Black Valentine’ are resistant or tolerant to Mexican bean beetles. In the home garden, handpick and destroy beetles and egg masses. Destroy crop refuse after harvest by working it into the soil or adding it to a compost pile.

Bean Leaf Beetle: The bean leaf beetle (Cerotoma trifurcata) is rarely a serious problem on beans or peas grown in South Carolina. The adults are about 1/5 to ¼ inch long. They vary considerably in color and markings, but are typically red to yellow, with three or four black spots in a row along the inner edge of each wing cover. Damage caused by bean leaf beetles is twofold: (1) girdling of stems near the soil line and (2) large irregular holes chewed in leaves. Damage to beans and peas early in the season may result in stand reduction.

Bean leaf beetle (Cerotoma trifurcata).
Bean leaf beetle (Cerotoma trifurcata).
Natasha Wright, Florida Department of Agriculture and Consumer Services, www.insectimages.org

Spider Mites: Two-spotted spider mites (Tetranychus urticae) are minute, eight-legged animals that are more closely related to spiders than to insects. Adults and immature stages appear as tiny specks on the undersides of leaves where they pierce the leaf surface and suck sap. Lightly infested leaves develop tiny whitish speckled spots, while heavily infested leaves turn pale yellow or bronze-colored and dry up. The undersurfaces of leaves usually are covered with silken webs over which the mites crawl. Spider mites develop rapidly during hot, dry weather and one generation can be completed in as few as eight days.

Insecticidal soaps generally offer adequate control when applied before the numbers are too high. Mites can be removed with a strong spray of water. Natural enemies such as lady bugs are important natural controls.

Stippling of bean leaves caused by two spotted spider mite (Tetranychus urticae).
Stippling of bean leaves caused by two spotted spider mite (Tetranychus urticae).
Whitney Cranshaw, Colorado State University, www.insectimages.org

Lima Bean Vine Borer: The lima bean vine borer (Monoptilota pergratialis) is an occasional pest of the large-stemmed bean varieties. The mature larva (caterpillar) is 7/8 inch long, bluish-green with a tint of pink on its back and has a yellowish-brown plate behind its dark head capsule. It burrows into stems, typically just above or below nodes (that part of the stem from which a leaf grows), and hollows out cavities. Infested stems form galls (a tumor-like swelling) which eventually turn brown and develop a woody texture. Infested plants are weakened and have lower yields.

Lima bean vine borer larva (Monoptilota pergratialis) and damage.
Lima bean vine borer larva (Monoptilota pergratialis) and damage.
Clemson University - USDA Cooperative Extension Slide Series, www.insectimages.org

Cabbage Looper: The cabbage looper (Trichoplusia ni) is another defoliator of peas and to a lesser extent beans. This larva (caterpillar) is green with a thin white line along each side of the body and two others near the middle of the back. Damage caused by loopers is ragged foliage. They rarely reach treatment status on peas and beans in the absence of other foliage feeders. Heaviest populations usually occur on late-planted crops.

Cabbage looper larva (Trichoplusia ni).
Cabbage looper larva (Trichoplusia ni).
Clemson University - USDA Cooperative Extension Slide Series, www.insectimages.org

Major Pod Feeders

Cowpea Curculio: The cowpea curculio (Chalcodermus aeneus) is the most destructive insect pest of southern peas grown in South Carolina. Cowpea curculios are rarely a problem on snap beans. Small, brown, wart-like or blister-like spots are found on pods damaged by curculios. These are caused when the adult punctures the pod to feed or lay eggs. Damaged peas have small, dark, indented spots and often contain grubs.

The cowpea curculio overwinters (survives the winter) as an adult in crop refuse or grass in the field or on the border of the field. Tufts of broom sedge, particularly at edges of woods, are favorite hiding places for overwintering adults. The adult is an oval, hump-backed, bronze-tinged, black “snout” beetle that has small dents on the wing covers and on the upper side of the body. It is about ¼ inch long. Adults begin to leave their winter quarters in March or early April. This emergence continues until June or July or about the time that the first peas are available for egg laying. These overwintering adults are long-lived and may survive through August.

Cowpea curculio adult (Chalcodermus aeneus).
Cowpea curculio adult (Chalcodermus aeneus).
Clemson University - USDA Cooperative Extension Slide Series, www.insectimages.org

Eggs are laid as soon as peas are formed in the pods. The weevil (also called the “snout” beetle) punctures the pod and chews a small hole in the surface of the pea. In this hole is laid a single egg. A legless, pale yellow, brown-headed grub hatches from this egg.

The grub feeds on one or more peas before it reaches its full size of slightly more than ¼ inch long. It then chews an exit hole through the pod and drops to the ground. It enters the soil to a depth of about 1 inch and transforms into a pupa (a nonfeeding stage where the larva changes into an adult).

Approximately seven or eight days elapse from the time that the eggs are laid until the grubs emerge from the pod. The larvae pupate (transform to pupae) about six days after they leave the pod. About 21 to 50 days are required to complete the life cycle. There are two generations each year. Because eggs are laid over an extended period of time, generations overlap and all stages can be present on southern peas at the same time.

Late southern peas isolated from early peas are usually not as severely damaged as early peas. Wild host plants produce pods that attract many curculios, and these can be a source of infestation.

The only feasible approach to the control of curculios is a preventive spray program. The current spray schedule recommended begins with a spray at first bloom and repeat treatments made on a five- to seven- day schedule.

Corn Earworm: The corn earworm (Helicoverpa zea) is primarily a problem on late-planted peas and beans, but early plantings may also be attacked. These worms vary greatly in color from a light green or pink to brown or nearly black and are lighter on the underparts. They are marked with alternating light and dark stripes running lengthwise on the body. The head is yellow and unspotted, and the legs are dark or nearly black. The corn earworm chews holes in both foliage and pods but prefers the latter. Levels requiring insecticide treatment are 5 percent damaged pods or one larva per 3 feet of row.

Corn earworm larva (Helicoverpa zea) on soybean.
Corn earworm larva (Helicoverpa zea) on soybean.
Clemson University - USDA Cooperative Extension Slide Series, www.insectimages.org

Tarnished Plant Bug: The tarnished plant bug (Lygus lineolaris) is a pest of snap and lima beans but rarely reaches pest status on southern peas. The bean growth period during which plant bugs are most important is full-bloom. The bugs withdraw plant sap and inject toxic saliva into the plant. The toxins may halt development of blooms and young pods and cause dark spots to develop on older pods that are attacked.

The adult bugs are about ¼ inch long by less than half as broad, flattened and oval in outline. They are a general brown color mottled with small, irregular patches of white, yellow, reddish-brown or black. Nymphs (immature forms) are similar in shape to adults with four black spots on the back. By late summer, adults and nymphs are numerous but because of their color and shy hiding habits, are not much noticed. Late-planted beans are highly susceptible to attack and should be checked closely during the bloom stage. Treatments for bugs should be made when there is an average of one bug per 6 feet of row.

Tarnished plant bug (Lygus lineolaris).
Tarnished plant bug (Lygus lineolaris).
Scott Bauer, USDA Agricultural Research Service, www.insectimages.org

Stink Bugs: The southern green stink bug (Nezara viridula) is a serious pest of lima beans and snap beans during late summer and fall. These bugs are shield-shaped, bright green, bad-smelling, flattened and about 5/8 inch long. The young (nymphs) are similar in shape and have black markings. Stink bugs damage beans in both the nymph and adult stages by sucking juices and injecting toxins. Although they may feed on leaves, pods are preferred. External signs of stink bug feeding on pods of snap bean show up as clear or water-soaked areas. On lima beans, the external damage on pods is not as clear. Inside the pod, developing beans become brown after bugs inject toxins and introduce yeast infections.

Southern green stink bug adult (Nezara viridula).
Southern green stink bug adult (Nezara viridula).
Merle Shepard, Gerald R.Carner, and P.A.C Ooi, Insects and their Natural Enemies Associated with Vegetables and Soybean in Southeast Asia, www.insectimages.org

On snap beans, insecticide treatment is necessary during bloom stage when there is an average of one bug per 10 feet of row. Lima beans are more sensitive to damage, and insecticide treatment is needed in the bloom stage when there is an average of one bug per 15 feet of row.

Control of Bean & Southern Pea Insects

Consult the discussion under each pest listed on this fact sheet for the “economic threshold” or the level of pest populations or plant injury necessary to warrant control measures.

The first choices for control of insect pests on vegetables always should be the lesser toxic pesticides. These will be less harmful to beneficial insects and have a much shorter pre-harvest interval or waiting period between spraying the crop and harvesting the vegetables. More than one application of an insecticide is typically required to control a pest. Always follow all label directions and observe waiting periods until harvest (pre-harvest interval).


Table 1. Natural, Less Toxic Pesticides and Contact Pesticides to Control Bean Pests.
PestsNatural, Less Toxic PesticidesContact Pesticides
Aphids Insecticidal soap
Neem oil extract
Pyrethrin
Bifenthrin
Malathion
Cyhalothrin
Bean Leaf Beetle Pyrethrin
Neem oil extract
Insecticidal soap
Carbaryl
Bifenthrin
Cyhalothrin
Thrips Insecticidal soap
Spinosad
Bifenthrin
Cyhalothrin
Corn Earworm
Bean Looper
Bacillus thuringiensis (B.t.)
Pyrethrin
Neem oil extract
Spinosad
Carbaryl
Bifenthrin
Cyhalothrin
Cowpea Curculio Pyrethrin
Neem oil extract
Bifenthrin
Cyhalothrin
Lesser Cornstalk Borer Bifenthrin
Cyhalothrin
Lima Bean Borer Carbaryl
Bifenthrin
Mexican Bean Beetle Pyrethrin
Neem oil extract
Carbaryl
Bifenthrin
Cyhalothrin
Malathion
Spider Mites Insecticidal soap Malathion
Bifenthrin
Stinkbug
Tarnished Plant Bug
Bifenthrin
Cyhalothrin
Malathion
Japanese Beetles Pyrethrin
Neem oil extract
Carbaryl
Bifenthrin
Cyhalothrin
Cucumber Beetle Pyrethrin
Neem oil extract
Soil drench w/ parasitic nematodes to control larvae
Carbaryl
Bifenthrin
Cyhalothrin
Grasshopper Bifenthrin
Cyhalothrin
Malathion
Lygus Bugs Bifenthrin
Cyhalothrin
Malathion
Whiteflies Insecticidal soap Bifenthrin
Cyhalothrin
Cutworms Protective collars
Molasses & grain bait w/ B.t.
Carbaryl
Bifenthrin
Cyhalothrin

Table 2. Insecticides for Bean & Southern Pea Pest Control.
Pesticide Active IngredientPre-Harvest Intervals (Days)Examples of Brand Names & Products
Natural, Less Toxic Insecticides
RTS = Ready to Spray (hose-end applicator)
RTU = Ready to Use (pre-mixed spray bottle)
PHI = Pre-harvest interval or number of days to wait after spraying before harvest.
Bacillus thuringiensis (B.t.) 0 American Brand Thuricide Concentrate
Bonide Thuricide B.t. Concentrate
Green Light B.t. Worm Killer Concentrate
Hi-Yield Thuricide Concentrate
Monterey B.t. Concentrate
Safer Caterpillar Killer with B.t. Concentrate
Southern Ag Thuricide Spray Concentrate
Tiger Brand Worm Killer Concentrate
Insecticidal Soap 0 Bonide Insecticidal Soap Multi-Purpose Insect Control Concentrate; & RTU
Espoma Earth-tone Insecticidal Soap Concentrate; & RTU
Natural Guard Insecticidal Soap Concentrate; & RTU
Safer Brand Insect Killing Soap Concentrate; & RTU
Schultz Garden Safe Insecticidal Soap Insect Killer Concentrate; & RTU
Neem Oil Extract 0 Bonide Neem Oil Fungicide, Miticide & Insecticide Concentrate; & RTU
Concern Garden Defense Multi-Purpose Spray Concentrate
Ferti-lome Rose, Flower & Vegetable Spray Concentrate
Garden Safe Fungicide 3 Concentrate; & RTU
Green Light Neem Concentrate
Monterey 70% Neem Oil Fungicide, Insecticide & Miticide Conc.; & RTS
Southern Ag Triple Action Neem Oil Concentrate
Safer BioNeem Insecticide & Repellent Concentrate
Pyrethrin 0 Bonide Garden Insect Spray Concentrate
Lilly Miller Worry Free Concentrate Insecticide & Miticide
Spectracide Garden Insect Killer Concentrate (with Pipernyl Butoxide)
Southern Ag Natural Pyrethrin Concentrate
Spinosad 3
(28 days for dried beans & dried peas)
Bonide Captain Jack’s Dead Bug Brew Concentrate; & RTS; & RTU
Bonide Colorado Potato Beetle Beater Concentrate
Ferti-lome Borer, Bagworm & Leafminer Spray Concentrate
Green Light Lawn & Garden Spray Spinosad Concentrate; & RTS
Monterey Garden Insect Spray Concentrate
Natural Guard Spinosad Landscape & Garden Insecticide RTS
Southern Ag Conserve Naturalyte Insect Control Concentrate
Contact Insecticides
Bifenthrin 3 Ferti-lome Broad Spectrum Insecticide Concentrate
Carbaryl 3 Bayer Advanced Complete Insect Killer for Gardens RTU
Garden Tech Sevin Concentrate; & RTS; & RTU
Cyhalothrin (lambda) 7 Spectracide Triazicide Insect Killer for Lawns & Landscapes Conc.; & RTS
Malathion 1 Bonide Malathion Concentrate
Gordon’s Malathion 50% Spray Concentrate
Hi-Yield 55% Malathion Insect Spray Concentrate
Martin’s Malathion 57% Concentrate
Ortho Max Malathion Insect Spray Concentrate
Spectracide Malathion 50% Insect Spray Concentrate
Southern Ag Malathion 50% EC

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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.