Pests

Below is an overview of many of the common arthropod pests encountered by Wisconsin vegetable producers and home gardeners. This page is currently under construction as we add more content to the individual pest profiles.

Jump to: BugsBeetlesLepsFliesThripsMitesAlphabetical list


Insects » Hemiptera (True bugs) »
Aphids
Aphids (Superfamily Aphidoidea), 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. Common species include asparagus, bean, cabbage, corn leaf, green peach, melon, pea, and potato aphids. More information…
Aster leafhopper
The aster leafhopper (Macrosteles quadrilineatus) is an olive, wedge-shaped insect that is 1/6 inch long and has six black spots on the vertex of the head. This leafhopper also migrates from southern states and carries the pathogen that causes carrot (aster) yellows disease. Aster yellows can be a serious problem on carrot, lettuce, celery, onion, and potato. For most crops, it is important to control the disease before symptoms show in the field. For susceptible crops such as lettuce and celery, one or two insecticide applications per week may be needed from seedling stage until harvest. More information…
Potato leafhopper
In Wisconsin, the potato leafhopper (Empoasca fabae) is a serious annual pest of snap beans and potatoes.  Damage caused by leafhoppers includes stunted plants, brown leaves and reduced plant vigor. A wide range of plants serve as hosts for the potato leafhopper (PLH), many are economically important crops.  These include alfalfa, apples, and all types of beans, clover, dahlia, eggplant, potatoes, rhubarb, soybeans, strawberries and other bedding plants. More information…
Squash bugs
Squash bugs (Anasa tristis) are an emerging problem in Wisconsin. In recent years, these insects have become more prevalent, causing damage to vine crops in commercial fields and home gardens alike. The key to management is early detection. Squash bugs feed on all vine crops, but pumpkins and squash are the preferred hosts with gourds and melons favored next. More information…
Tarnished plant bug
Tarnished plant bugs (Lygus lineolaris) are 1/4 inch, tan to dark brown oval insects with piercing sucking mouthparts. They attack more than 50 different economic crops but are most damaging to strawberries, peppers, and all bean crops in Wisconsin. Feeding by these insects causes poor fruit set and gnarled fruit due to the toxic saliva they inject into the plant. They are highly mobile insects that overwinter in field debris. Large numbers of adult plant bugs migrate out of alfalfa fields when hay is cut. For both potatoes and commercial beans, take 25 sweeps with an insect sweep net per sample site with at least 10 sample sites per 100 acres. When counts exceed one tarnish plant bug per sweep on a field average, control measures are recommended in potato and snap bean.
Insects » Coleoptera (Beetles) »
Asparagus beetle
The common (Crioceris asparagi) and spotted (Crioceris duodecimpunctata) asparagus beetles are annual pests of asparagus in Wisconsin. The common asparagus beetle is the most prevalent and the only one that causes economic damage to asparagus. More information…
Bean leaf beetle
The bean leaf beetle (Cerotoma trifurcata) is 1/4 inch long, ranges in color from yellow-green to red, and features four black spots in its back. Adult feeding can reduce plant vigor and yield by chewing small holes in leaves. Adults also feed on developing pods, causing distortions and making them more prone to infection from pathogens. Larvae feed on roots, nodules, and below-ground stems. More information…
Colorado potato beetle
The Colorado potato beetle (Leptinotarsa decemlineata) is the most distinctive pest of potatoes. Both the yellow-and-black striped adults and the brick-red humped larvae feed on the foliage. Feeding normally is initiated on the terminal growth and can be severe. Adults overwinter and move to emerging potatoes early in the spring (May). The adults lay bright yellow egg masses, and larvae feed for several weeks in the summer before pupating in the soil. Emerging adults then continue feeding throughout the season until no vines remain. More information…
Corn rootworm
Rootworm (genus Diabrotica) larvae are white with black heads and grow 1/2 inch long. Northern and western rootworm larvae cannot be differentiated in the field. They feed on crown roots from June to August, causing corn to lodge and “gooseneck.” Rootworms are most serious in loam soils but are of little consequence in muck or non-irrigated sandy soils. The larvae are not a potential problem unless corn is planted on the same ground in a “rootworm area” for 2 or more years in succession. Annual crop rotation controls these insects, because eggs overwinter in the soil.   More information…
Cucumber beetles
The striped (Acalymma vittatum) and spotted (Diabrotica undecimpunctata) cucumber beetles are 1/4-inch, yellow-green beetles that become active in very early spring. Adults feed on developing fruit and foliage and, more importantly, transmit bacteria causing wilt disease. Small numbers of beetles can devastate a planting if they carry the disease, and they must be controlled before the disease appears. In the fall, adults of these beetles can chew holes in the developing fruit of vine crops such as cucumber, melon, pumpkin, and squash. More information…
Flea beetles
Flea beetles (Tribe Alticini) are frequently a pest of early plantings. These small, shiny black beetles, which jump when approached, chew small circular holes in the leaves. This damage is insignificant on large potatoes and tomatoes but young seedlings can be rapidly killed.Young seedlings or transplants of cabbage, broccoli, beet, tomato, eggplant, and all vine crops should be scouted on a weekly basis when they are young. If flea beetle activity is seen, an insecticide rescue treatment will be needed. More information…
 
Japanese beetles
Japanese beetle (Popillia japonica) adults are 3/8 inch long and a metallic green color, with copper wing covers and a series of white dots along the side of the abdomen. The larvae are a serious pest of turfgrass in late summer. Adults are active from late June to September and feed on the flowers, fruits, and leaves of a wide variety of plants, including asparagus, tomato, and eggplant. Trapping measures may actually attract more beetles and cause more damage. More information…
White grubs
This insect, which is the larval stage of the June beetle, has up to a 3-year life cycle. Because the adults lay eggs in grassy sodded areas, fields located in plowed-down sodded areas are most susceptible. The characteristic C-shaped grubs feed on the roots of most plants. They are most damaging to root crops such as carrots or potatoes. Tilling the soil to expose the larvae during the spring and fall helps reduce numbers. Granular insecticides can be worked in the soil before planting in areas where damage is expected. Established weed-free fields should have few problems.
Wireworms
This insect is the larval stage of the click beetle (family Elateridae) and, like the white grub, lays eggs in grassy areas. Wireworms are also troublesome in low, poorly drained areas. Weed control is the best preventative measure. Control procedures for white grubs will also control wireworms. Potatoes and carrots are the most susceptible crops. Grassy or old sod fields will have high populations of wireworms. A soil insecticide should be worked in pre-plant in these fields. More information…
Insects » Lepidoptera (Moths, butterflies, Caterpillars) »
Armyworms
Armyworms are dark caterpillars measuring up to 2 inches long. They have a dark stripe running lengthwise on the side with a yellow stripe beneath. Dark and light stripes alternate along their back. Armyworms move up from grassy weeds within cornfields or migrate into cornfields from small grain or forage fields. They may hide in soil crevices and beneath clods by day. At night, they chew corn leaves and weaken plants.
Cabbage looper
Imported cabbageworms (Pieris rapae), cabbage loopers (Trichoplusia ni) and diamondback moths (Plutella xylostella) are the three most significant caterpillar pests of Wisconsin cole crops, with the imported cabbage worm being the most significant. The cabbage looper attacks beets, celery, lettuce, peas, potatoes, spinach and tomatoes, in addition to cole crops. Damage caused by these pests is generally of little economic importance in Wisconsin. More information…
Common stalk borer
Eggs of the common stalk borer (Paipanema nebris), a cutworm relative, are laid in grassy weeds in September. In late May to July, the brown-and-white striped caterpillars migrate into fields and burrow into the stems of tomatoes, potatoes, beans, and other thick-stemmed plants. Once inside the stem, the insect cannot be controlled. Fall grass control will prevent egg laying and is the best control method for common stalk borer.
Corn earworm / Tomato fruitworm
Corn earworm (Helicoverpa zea) caterpillars are varicolored, smooth, up to 2 inches long and feed mostly on ear tips. Insecticide treatment is necessary for early market sweet corn and for late-season canning or market sweet corn (silking after August 15). More information…
Cutworms
These are the larval stage (caterpillar) of night-flying moths. They are whitish gray to brown worms, ranging from 1/2 to 2 inches long. They feed almost exclusively at night and hide in the soil during the day. All cutworms curl to a characteristic tight ball when exposed, making them easy to identify. Most cutworms cut plants off at or slightly below the soil surface, making recent transplants especially susceptible. Eventually, plants become too thick and tough for cutworms to feed. Adult females are attracted to tall grasses for egg laying, and cutworm numbers tend to be higher in weedy or trashy fields. Almost all commercial vegetable crops such as asparagus, beets, onions, carrots, celery, and potatoes can be attacked by cutworms. It is very difficult to predict when and where an infestation will spring up, and pre-plant insecticide treatments will not control heavy cutworm infestations. Scouting fields on a weekly basis is the best method for monitoring cutworm activity. If damaging populations are found, a “rescue” treatment will be needed. Bait formulations are the preferred treatment if conditions are dry, whereas both baits and sprays can be used when the cutworms are feeding at the soil surface.
Diamondback moth
Imported cabbageworms (Pieris rapae), cabbage loopers (Trichoplusia ni) and diamondback moths (Plutella xylostella) are the three most significant caterpillar pests of Wisconsin cole crops, with the imported cabbage worm being the most significant. Diamondback moths are worldwide pests of cabbage and leafy greens, and have developed resistance to numerous insecticides and several products containing Bacillus thuringiensis (Bt). Damage caused by these pests is generally of little economic importance in Wisconsin. More information…
European corn borer
European corn borer (Ostrinia nubilalis) larvae are between 3/4 to 1 inch long and range in color from grey to creamy white, with a black head and numerous spots over the body. In most of Wisconsin, two generations of eggs are laid on the undersides of leaves. First generation larvae typically cause damage only to leaves and stalks, unless the corn is already tasseling, in which case the larvae will enter the ear. In Southern Wisconsin, begin checking early sweet corn for egg masses by June 15th. Second generation larvae develop from eggs laid in mid-August and cause heavy infestations in late-planted corn. Direct feeding on kernels may make sweet corn unmarketable. More information…
Hornworms
The tomato hornworm is a very large green worm (up to 3 inches) with a spine on the posterior end and white side stripes. The larva feeds on both foliage and fruit, and because each larva eats three to four times its weight in food daily, the damage appears dramatic. The adult stage of this insect is a gray hawk moth that is often mistaken for a hummingbird because it feeds on flowers. Because they are usually found in small numbers, hornworms rarely need control. More information…
Imported cabbageworm
Imported cabbageworms (Pieris rapae), cabbage loopers (Trichoplusia ni) and diamondback moths (Plutella xylostella) are the three most significant caterpillar pests of Wisconsin cole crops, with the imported cabbage worm being the most significant. Damage caused by these pests is generally of little economic importance in Wisconsin. More information…
Squash vine borer
The squash vine borer (Melittia cucurbitae) is an annual pest of pumpkins and squash. Often, it is not recognized as a potential pest until too late and as a result, can produce a negative economic impact in some years. Winter squash is highly susceptible to attack. More information…
Insects » Diptera (Flies and maggots) »
Cabbage maggot
The adult cabbage maggot (Delia radicum) is a small gray fly that lays its eggs at the base of crop plants in the cabbage family. The small, cylindrical white eggs hatch into legless white maggots that feed on the roots. Seedling plants can be killed rapidly, while transplants tend to wilt and die slowly. Root crucifers such as radish and turnip show surface tunneling that is often accompanied by soft rots. More information…
Onion maggot
Onion maggots (Delia antiqua) are small whitish larvae found in the bulbs of onions. The adult is a grayish fly that resembles the cabbage maggot. Onion maggots are a problem after a series of cool, wet springs. The most effective way to control these insects is to apply an insecticide in the furrow when planting. More information…
Seedcorn maggot
Seed corn maggot (Delia platura) is by far the most serious pest of all beans. The white legless maggot burrows into the seed or seedling, causing very poor seed germination and emergence, and/or stems without leaves (snake heads). The adult is a small grayish fly that looks identical to the cabbage maggot. More information…
Vegetable leafminer complex
The term leafminer is commonly used to describe flies, moths, sawflies or beetles in the larval stage. However, leafminers that feed on vegetables most commonly belong to the order Diptera – the flies. Leafminers feed on the mesophyll tissue between the upper and lower surfaces of leaves. This region of the leaf is where the plant converts light to energy through the process of photosynthesis. Economic crop damage occurs most often in vegetables harvested for edible foliage, such as spinach or chard. More information…
Insects » Thysanoptera (Thrips) »
Thrips
Thrips are small 1/25-inch insects that cause whitish scratches or brownish blotches on plant leaves. Hot dry weather is correlated with severe thrips problems. Thrips attack cabbage and cause a brownish scarring in the head of processing cabbage. Thrips must be controlled before the plant heads out in order to assure proper coverage and control. In onions the injury looks similar to both ozone injury and some diseases. Use large volumes sprays (100 gallons/acre) with a wetting agent for thrips control. A second treatment 5 to 7 days later may be warranted.
Arachnids » Acari (Mites) »
Spider mites (Family: Tetranychidae)

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