All posts by hudelson


Wireworms are the larvae of several species of click beetles (Family Elateridae).  These beetles flip into the air with an audible click when turned on their backs.  Wireworms feed primarily on grasses (including grass crops such as corn) but have a broad host range that includes vegetables (e.g., beans, beets, cabbage, carrots, lettuce, onion, peas, potatoes and radishes) and herbaceous ornamentals.  Wireworms can be found virtually anywhere, and they are very common in old fields or grass pastures, which are attractive egg-laying sites for female click beetles.  Wireworms tend to cause their most significant damage in poorly drained areas, particularly if sod has been plowed under within the past one to four years.

A wireworm or click beetle larva (left) and an adult click beetle (right). Photos courtesy of Karen Delahaut (left) and PJ Liesch (right).
A wireworm or click beetle larva (left) and an adult click beetle (right). Photos courtesy of Karen Delahaut (left) and PJ Liesch (right).

Appearance:  Wireworms are thin, shiny, jointed, yellow to reddish-brown, worm-like larvae resembling mealworms.  They range in length from 1/4 to 11/2 inches and are approximately 1/8 inch wide.  Different species are distinguished by the ornamentation on the last segment of their bodies.  Adult wireworms (click beetles) are hard-shelled, brown or black, “streamlined” beetles that make a clicking sound when they right themselves after being overturned.

Symptoms and Effects:  Adult wireworms (click beetles) do not cause plant damage.  However, larvae can feed on seeds and developing seedlings, as well as on the roots and underground stems of older plants.  Damage often occurs in localized areas in a planting.  Seed feeding prevents or delays germination.  Seedling feeding (often characterized by the presence of small holes in cotyledons and stems) can stunt or kill plants.  Seed/seedling feeding typically leads to uneven and reduced stands.  Wireworm feeding on smaller roots of older plants leads to stunted roots with brown discolorations.  Feeding on larger roots and underground stems leads to visible trails or small tunnels.  Root and underground stem damage can lead to stunted growth and wilting above ground, particularly if plants are small or under stress (e.g., water stress).  Wireworms can be particularly problematic on potatoes where they burrow into tubers, making the tubers unusable.

Life Cycle:

Wireworms have an extended life cycle, taking from one to six years to complete a single generation.  They can overwinter as either adults or larvae.  Adults emerge in the spring.  Females spend most of their 10 to 12 month life span in the soil laying eggs (up to 100 eggs per female), usually in grassy, weedy areas in gardens and fields.  Eggs hatch over a period of several days to several weeks depending on the temperature.  Larvae move short distances to feed on seeds and roots.  They prefer moist, cool, heavy soils and typically live in the upper six inches of the soil.  However, during dry weather, they may burrow deeper.  Because of their extended life cycle, larvae of some species of wireworms will feed for up to six years before pupating.  Adults emerge the spring after the pupae form.

Scouting Suggestions:

No thresholds for wireworms have been identified, so routine scouting is not recommended.  However, watch for wireworms in the soil when you till your home garden.  Also check for larvae near ungerminated seeds, in the roots and lower stems of damaged plants and in the upper four to six inches of soil in any suspect area.

Alternatively, if you are a commercial vegetable grower, you can monitor for wireworms using bait stations that you can set up in the fall or spring.  Use at least ten bait stations per 40 acre field to obtain an accurate estimate of the number of wireworms in an area.  For each station, prepare bait by soaking approximately one cup each of untreated corn and wheat seed in water for 24 hours to encourage germination.  At each bait station, place seeds into a six inch deep hole that is several inches wide.  Cover the seeds with soil, then with a small piece of black plastic, and then with a securely anchored piece of clear plastic.  The plastic will help the sun heat the soil, speeding seed germination.  The germinating seed will attract wireworms from the surrounding soil.  Check the bait stations after one week by digging up the germinating seeds and counting the number of wireworms in with the seeds.  Consider chemical control if there is an average of one or more wireworm per station.


Non-Chemical:  Prior to planting, improve drainage in those areas where the soil drains poorly.  Rotate crops appropriately [see University of Wisconsin Garden Facts XHT120 (Using Crop Rotation in the Home Vegetable Garden) for details] and avoid growing vegetables that are especially susceptible to wireworm damage, particularly in areas where wireworms have been a problem in the past.  DO NOT plant too early into cold soils.  Instead, plant later when soils are warmer.  Late planting will speed germination, allow plants to establish quickly and reduce the amount of time that plants are in the early stages of growth where wireworms can cause more severe damage.  Be diligent about controlling weeds in areas where you are growing your vegetables, and also consider not growing crops for a summer (while still keeping weeds under control) in areas where wireworms have been a serious problem.

Chemical:  Because severe outbreaks of wireworms are rare, insecticide use typically is not warranted.  If you have had a history of wireworm problems and believe that treatments are needed, incorporate insecticides into the soil prior to planting.  DO NOT apply insecticides once you have observed wireworm damage, as treatments at that point are typically not effective.  For a complete listing of products for wireworm control, see Commercial Vegetable Production in Wisconsin (Extension Bulletin A3422, available at

For more information on wireworms:  See Extension Bulletin A3422, or contact your county Extension agent.

Onion Thrips

Onion thrips (Thrips tabaci) are an important annual pest of onion. They can attack many garden crops, but most commonly cause serious damage to onions, leeks and garlic.

Onion thrips damage to onion leaves (left) and numerous onion thrips adults and nymphs on an onion leaf (right). Phots courtesy of Karen Delahaut (left) and Joe Ogrodnik, Cornell University (right).
Onion thrips damage to onion leaves (left) and numerous onion thrips adults and nymphs on an onion leaf (right). Phots courtesy of Karen Delahaut (left) and Joe Ogrodnik, Cornell University (right).

Appearance:  Adult onion thrips are about 1/12 inch long, thin and pale yellow to brown in color.  Their wings have only a single, central vein and are fringed with long hairs.  Nymphs (immature thrips) resemble adults, but they are smaller and lack wings.

Symptoms and Effects:  In general, onion thrips prefer tight spaces and cause severe damage on plants that produce tightly packed leaves.  Feeding causes whitish blotches that may appear as silvery streaking on leaves.  As feeding continues, affected tissue may turn dry and yellow, and may eventually brown and die.  On flowering plants, thrips feeding can cause decreased pollen production.  Onion thrips can also carry and inoculate plants with viruses such as Iris yellow spot virus (IYSV), Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INSV).  See University of Wisconsin Garden Facts HXT1139, Impatiens Necrotic Spot, for details on this latter virus.

On onions, thrips prefer to feed on the youngest leaves, and the tips of these leaves often brown and die.  Thrips feeding can also lead to distorted and undersized bulbs.  Cultivars that produce leaves close to the stems are more susceptible to thrips damage than cultivars with more open growth.  Onions that have a more circular leaf structure and that have glossier foliage tend to be less prone to damage.  Red onions are particularly susceptible to thrips damage, while Spanish onions tend to be somewhat more tolerant.

On cabbage, varieties with dense heads are most susceptible to damage.  Heavy thrips feeding can cause cabbage heads to become distorted and leaves to have darkened blisters where feeling has occurred.  On cauliflower, thrips damage causes tan or brown streaks on the curds.  This damage can provide entry points for bacteria that cause bacterial soft rot (see University of Wisconsin Garden Facts HXT1224, Bacterial Soft Rot, for details).

Life Cycle:  Onion thrips overwinter in legume (e.g., alfalfa) and grain (e.g., wheat) fields, in weedy areas, and in onion bulbs not removed from onion fields.  Females can reproduce without mating and lay eggs on the undersides of leaves.  Eggs hatch after five to 10 days.  The first two thrips nymphal stages feed on plants.  Two additional non-feeding nymph stages live in the soil or on the soil surface.  Nymphs mature into adults after 15 to 30 days, and adults return to plants to feed.  Thrips can produce five to eight generations per year, and outbreaks are most likely to occur in the summer during hot, dry periods.

Scouting:  Thrips populations can develop very rapidly.  Be sure to routinely and carefully monitor crops for thrips during the periods indicated in the table below.  Use yellow or white sticky traps and carefully examine plants at the edge of home gardens (or commercial fields) to monitor for the initial movement of thrips early in the growing season.  If you find three thrips per onion leaf, consider chemical treatments.  However, some onion varieties (e.g., ‘Snow White’, ‘Vega’) are highly tolerant of thrips feeding even with up to 45 thrips per plant.

When to Scout for Onion Thrips

July August September
Early Mid Late Early Mid Late Early Mid Late


Cultural:  Remove plant debris from gardens (and commercial fields) as well as any areas surrounding a location where you will be growing onions or other susceptible vegetables.

Chemical:  Apply insecticides each year as soon as thresholds (see above) have been exceeded to target the insects before they can reach protected areas (e.g., the insides cabbage heads and onion necks) where insecticides cannot easily penetrate.  When using foliar sprays, direct the sprays down into the center of the plants to maximize penetration into protected areas.  Also, use sufficient water, as well as a spray additive, to help the insecticide penetrate.  Alternate use of at least two insecticide active ingredients to minimize development of insecticide-resistant thrips.  See UW-Extension Publication A3422, Commercial Vegetable Production in Wisconsin, for a list of registered insecticides.

For more information on onion thrips:  See UW-Extension Bulletin A3422, or contact your county Extension agent.

Potato Leafhopper

Potato leafhopper (PLH), Empoasca fabae, is a potentially serious annual pest of a wide range of plants including, but not limited to, alfalfa, apple, beans (all types), clover, dahlia, eggplant, potato, rhubarb, soybean, strawberry and many types of bedding plants.  In Wisconsin, PLH is of particular concern in commercial snap bean and potato production.

Potato leafhopper adult and nymph.  Photo courtesy of Arthur Hower, Penn State University
Potato leafhopper adult and nymph. Photo courtesy of Arthur Hower, Penn State University

Appearance: The adult PLH is a highly mobile, small (1/8-inch long), bright-green, wedge-shaped insect.  Its body is widest at the head and tapers toward the wing tips.  A PLH typically has six white spots on the front margin of its prothorax (i.e, the body part to which its first pair of legs is attached).  PLH’s have piercing-sucking mouthparts and quickly jump, fly or run sideways when disturbed.  PLH nymphs (i.e., immature stages) are smaller than adults, pale green to yellow, and wingless.

Symptoms and Effects:

Adult and nymph PLH’s feed by inserting their mouth parts into a plant’s vascular tissue (specifically the food-conducting tissue called the phloem) and extracting sap.  This feeding physically injures the plant.  In addition, saliva that PLHs inject into a plant contains toxic compounds, causing further damage.  PLH feeding plugs a plant’s vascular tissue and permanently reduces a plant’s ability to efficiently photosynthesize.  Typically, nymphs cause more damage than adults.

PLH’s can feed on plants for several weeks before their damage becomes obvious.  Symptoms develop most rapidly during hot, dry weather.  Initial symptoms of leafhopper feeding include paling of leaf veins and curling of leaves.  After continued feeding, a characteristic triangular yellowing or browning of leaf tips (called hopperburn) develops.  As symptoms progress, yellowing and browning spread inward from leaf margins, and eventually, entire leaves die.  Plants with PLH damage can become stunted and yellow with upward-curled leaves (typical for snap beans).  If PLH populations are high, plants can die (typical for potatoes).  PLH damage can result in substantial yield loss.

Life Cycle:  Potato leafhoppers do not overwinter in Wisconsin.  They blow into the state each spring on southerly winds, typically arriving in mid to late May.  Female PLHs live approximately one month and lay two to three tiny, white eggs each day in stems and large leaf veins of host plants.  Tiny nymphs emerge from these eggs in seven to 10 days, molt five times over a period of approximately two weeks and then turn into adults.  There are typically two PLH generations per year in Wisconsin.  In June and early July, PLH populations often appear to “explode” overnight, because large numbers of PLHs migrate from alfalfa fields that are harvested at that time.  PLH numbers typically decline significantly in August.

Scouting Suggestions:Snap beans and potatoes should be monitored regularly for PLH activity, especially in early summer after alfalfa is cut.  For snap beans, PLHs cause their greatest damage when plants are in the seedling stage.

When to Scout for Leafhoppers

Crop May June July August September
Early Mid Late Early Mid Late Early Mid Late Early Mid Late Early Mid Late

If you are a home gardener or a commercial grower, visually inspect susceptible vegetables, particularly snap beans and potatoes, for PLH nymphs.  In addition, if you are a commercial vegetable grower, use sticky cards at field edges and sweep nets within fields to monitor for PLH adults.  Set up at least five sample sites per 30 acres, and take 25 sweeps per sample site.  Also, examine the undersides of 25 leaves at each sample site.  Select leaves from the middle to lower half of the plant.  See the table below for details on when insecticide treatments should be considered.

Leaves showing potato leafhopper damage from none (upper left) to severe (lower right).  Photo courtesy of Jeff Wyman
Leaves showing potato leafhopper damage from none (upper left) to severe (lower right). Photo courtesy of Jeff Wyman


Cultural:  Avoid planting sensitive crops near alfalfa fields, because PLHs will migrate from alfalfa to these crops when the alfalfa field is harvested.  Healthy, vigorously growing plants withstand PLH damage more effectively than stressed plants.  Therefore, make sure you are watering and fertilizing your plants adequately, as well as following cultural practices (e.g., proper weed control) that reduce plant stress and optimize plant growth.

Several insect predators, fungal pathogens and parasites attack PLHs, although none have been shown to be effective in controlling PLHs.  In addition, little information exists on tolerances of different varieties of plants to PLH damage.  In snap beans, however, Blue Lake cultivars are known to be more susceptible to PLH damage than Tendercrop lines.  Also, vegetable varieties with hairier leaves appear to be less attractive to PLHs and thus less prone to PLH damage.

Chemical:  Chemical insecticides provide the most effective control for PLHs.   Seed treatments and systemic treatments applied at planting can provide excellent control of PLHs.  Many foliar insecticides also provide excellent control.  Refer to the University of Wisconsin-Extension publication Commercial Vegetable Production in Wisconsin (A3422) for full list of insecticides and recommendations.

When to Treat for PLH:  Threshold Levels for Selected Vegetables

Larger Snap Bean Threshold Potato
Nymphs 1 per 10 leaves 1 per 10 leaves 21/2 per 25 leaves
Adults 1 per 2 sweeps 1 per sweep 1/2 to 1 per sweep

For more information on potato leafhoppers:  See Extension Bulletin A3422 (Commercial Vegetable Production in Wisconsin) or contact your county Extension agent.

Cucumber Beetles

Striped and spotted cucumber beetles are common pests of vine crops (e.g., cucumber, squash, pumpkin, watermelon) that can cause severe damage to roots, leaves, flowers and fruits, as well as interfere with pollination, leading to reduced fruit set.  In Wisconsin, the striped cucumber beetle is the more common of the two insects.  In addition to direct damage from their feeding, cucumber beetles can contribute to indirect vine crop damage because they can carry and transmit disease-causing bacteria and viruses.

Striped cucumber beetle (top) and spotted cucumber beetle (bottom).
Striped cucumber beetle (top) and spotted cucumber beetle (bottom).

AppearanceStriped cucumber beetle (Acalymma vittatum) adults are between 3/16 and 1/4 inches long and yellow-green in color with three black stripes running the length of their bodies.  They are often confused with western corn rootworm beetles, which are not vine crop pests, but which are often found feeding on vine crop pollen.  You can distinguish between these two insects by examining their undersides.  Striped cucumber beetles have black abdomens; western corn rootworms have yellow-green abdomens.  Spotted cucumber beetle (Diabrotica undecimpunctata) adults are similar in size to striped cucumber beetle adults and are yellow-green except for their black heads and 12 black spots on their backs.  Larvae of both types of cucumber beetle live in the soil and are worm-like, are white with a dark head, and have three pairs of legs.

Symptoms and Effects:  Cucumber beetle larvae feed on roots and stems, and they can stunt or kill seedlings and transplants when present in large numbers.  Adults feed on leaves, petals, pollen, and fruit.  Plants in the cotyledon to three leaf stages are especially vulnerable, and high adult populations can completely defoliate plants.  Leaf feeding on older plants can lead to moderate to severe defoliation.  Fruit feeding can cause cosmetic blemishes that do not reduce fruit edibility but can make fruit less marketable.  In addition, cucumber beetle can cause reduced fruit set by congregating in high numbers in flowers (attracted by compounds called cucurbitacins that are produced by the flowers) and disrupting pollination by bees.

In addition to direct damage to plants, cucumber beetles can also inoculate vine crops with Erwinia tracheiphila, the bacterium that causes bacterial wilt [see University of Wisconsin Garden Facts XHT1229 (Bacterial Wilt of Cucurbits) for details].  This disease is typically fatal.  Cucumber beetles can also carry and transmit Squash mosaic virus.  This virus can lead to stunted plants with distorted, blotchy-colored leaves.  The virus can also reduce fruit yield and make fruits malformed and blotchy in color.  Home gardeners often find these fruits unattractive and unappetizing.  For this reason, commercial growers often find the distorted, blotchy fruits unmarketable.

Life Cycle:  Only striped cucumber beetles overwinter in Wisconsin.  Adults emerge in mid- to late May and lay eggs in the soil at the base of vine crops.  Eggs hatch in 14 to 21 days and larvae feed on roots and underground parts of stems.  After two to three weeks of feeding larvae pupate in the soil.  Spotted cucumber beetles migrate to northern locations in early to mid-July.  This late arrival makes them less likely to be a serious problem.  There is one generation of striped and spotted cucumber beetles per year.

Scouting:  Early detection and control of cucumber beetles is critical for preventing problems with bacterial wilt.  Monitor vine crops for adult beetles two to three times per week early in the season, and weekly thereafter.  Pay close attention to the edges of areas where vine crops are grown.  This is where cucumber beetles congregate.  The threshold for treating for cucumber beetles is one beetle
per plant in cucumbers, melons, Hubbard and butternut squash, and younger pumpkins, and five cucumber beetles per plant in watermelon, other varieties of squash, and older pumpkins.  If beetle populations exceed 20 per plant, transmission of the bacterial wilt bacterium may occur before insecticide treatments have a chance to control the beetles.


CulturalRotate vine crops with grains, tomatoes, or a non-host cover crop to delay cucumber beetle infestations.  Also, consider planting blue Hubbard squash at the edges of areas where you are growing vine crops.  This squash variety is particularly attractive to cucumber beetles and will serve as a trap crop where the insects are more likely to feed.  If you decide to use a trap crop, it is critical to control cucumber beetles on the trap plants.  Otherwise they will eventually spread to other nearby vine crops.

Also consider variety selection when attempting to manage cucumber beetles.  Cucumber varieties differ in their attractiveness to the insects.  In general, less bitter cucumber varieties are less likely to attract cucumber beetles.  In cantaloupe, the varieties ‘Makdimon’ and ‘Rocky Sweet’ are less attractive to these insects.  In addition, certain cucumber varieties (e.g., ‘Liberty’ and ’Wisconsin SMR-58’) are tolerant of cucumber beetle feeding damage.

In smaller plantings, consider using floating row covers to keep cucumber beetles from reaching plants.  When using floating row covers, be sure to uncover plants when they flower to allow bees to enter and pollinate.

If you see evidence of bacterial wilt, remove diseased plants immediately to prevent further spread.

Chemical:   Several insecticides are available to manage cucumber beetles when numbers exceed established thresholds (see above).  If beetle populations are particularly high however, chemical treatments may have limited benefit.  See Commercial Vegetable Production in Wisconsin (Extension Bulletin A3422, available at for a complete listing of products.  Note that not all of the listed products may be available for use in home gardens.  If you decide to use insecticides, contact insecticides should be applied to seedlings before transplanting if large numbers of beetles are present early in the season.  Systemic insecticides can be applied as either drench applications, or through drip irrigation to target the roots of developing plants.  Additional foliar insecticides may be necessary later in the growing season and should be continued as needed after systemic insecticides lose their effectiveness (typically 55 to 70 days after planting) or when established thresholds are exceeded.

Note that cucumber leaves are sensitive and can be burned by insecticide sprays, particularly if they are applied with other pesticides (e.g., fungicides), or if they are applied when daytime temperatures are above 85°F.  To avoid harming beneficial insects and pollinators, be sure to spray in the late afternoon or the evening.

For more information on cucumber beetles: See Extension Bulletin A3422 (available at, or contact your county Extension agent.

Ralstonia Wilt – Pest Alert

What is Ralstonia wilt?  Ralstonia wilt (also sometimes known as Southern wilt) is a usually lethal disease that affects over 250 plants in over 40 plant families.  Susceptible greenhouse-grown ornamentals include, but are not limited to, plants in the genera Capsicum, Cosmos, Cyclamen, Dahlia, Fuschsia, Gerbera, Hydrangea, Impatiens, Lantana, Nasturtium and Pelargonium.  Vegetables such as eggplant, pepper, potato and tomato, as well as tobacco, are also susceptible.  Ralstonia wilt was first reported on geraniums (Pelargonium spp.) in Wisconsin in 1999.  In 2020, the disease was reported on Fantasia © ‘Pink Flare’ geraniums in Michigan.  Potentially infected ‘Pink Flare’ geraniums were also distributed to 38 other states including Wisconsin.

Yellowing and wilting characteristic of Ralstonia wilt. Photo courtesy of WI DATCP
Yellowing and wilting characteristic of Ralstonia wilt. Photo courtesy of WI DATCP

What does Ralstonia wilt look like? Symptoms of Ralstonia wilt in geraniums are similar to those associated with bacterial blight (caused by Xanthomonas campestris pv. pelargonii).  Initially, lower leaves of infected plants yellow and wilt, then die.  Yellowing and death of upper leaves follow.  Symptoms may initially occur on only one side of the plant.  Internally, the water-conducting tissue of the plant browns, and then the entire stem rots from the inside out.  Eventually, infected plants die.

Where does Ralstonia wilt come from? Ralstonia wilt is caused by the bacterium Ralstonia solanacearum (formerly Pseudomonas solanacearum).  This bacterium is commonly found in tropical, sub-tropical and warm temperate climates, but is not believed to survive cold temperatures such as those typical of Wisconsin winters.  The bacterium can be moved in symptomless plants or cuttings, or in contaminated soil and plant debris (where the pathogen can remain dormant for many years).  Several subgroups (i.e., races and biovars) of R. solanacearum have been recognized, each with a different host range.  R. solanacearum race 3, biovar 2 is of particular concern because it causes a serious disease of potato called brown rot.  In addition, this race/biovar has been listed as a select agent by the U.S. government and is considered to have potential to be developed as a bioterrorist weapon against U.S. agriculture.

How do I save plants with Ralstonia wilt? There are no known treatments that will save plants affected by Ralstonia wilt.  If you believe your plants are suffering from this disease, immediately contact your local department of agriculture or county Extension agriculture or horticulture agent to arrange for confirmatory testing.  If you live in Wisconsin, you can contact the UW-Madison Plant Disease Diagnostics Clinic (see below for contact information) for assistance.  If your plants test positive for R. solanacearum race 3, biovar 2 the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) must be notified and this organization will provide guidance on proper disposal of contaminated plants, as well as decontamination of greenhouses or other sites where contaminated plants have been grown.

How do I avoid problems with Ralstonia wilt in the future? Start by purchasing and growing pathogen-free plant cuttings.  Keep plants from different suppliers physically separated by at least 4 ft. to minimize the risk of cross contamination should a shipment of plants prove to be contaminated.  Because R. solanacearum is easily moved with soil or water, minimize splashing or any other movement of water or soil from plant to plant when watering.  When taking cuttings or trimming plants, be sure to clean cutting tools between cuts using an approved disinfectant.  For a complete list of such products, contact the UW-Madison Plant Disease Diagnostics Clinic (see below for contact information).  Also wear disposable gloves (nitrile are best) when handling plants, and change gloves between working with different geranium varieties.  This will minimize the possibility of moving R. solanacearum by touch.  If gloves are not available, wash your hands frequently and thoroughly (especially between geranium varieties) with lots of soap and water or with an alcohol-based hand sanitizer.  Remove and destroy weeds or weed debris as these can harbor the pathogen.  Finally, do not grow plants in a greenhouse where the disease has occurred unless it has been properly decontaminated.

For more information on Ralstonia wilt or help in diagnosing this problem:  Contact Brian Hudelson, Plant Disease Diagnostics Clinic, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI  53706-1598 [phone: (608) 262-2863, fax: (608) 263-3322, email:


Tomato hornworms (Manduca quinquemaculata) and tobacco hornworms (M. sexta) are large, blue-green caterpillars (larvae) with a spine (horn) on the posterior (rear) end.  These insects do not typically cause significant damage in commercial vegetable fields.  However, large numbers of larvae can occasionally occur in home gardens, leading to significant damage.  Tomato and tobacco hornworms feed only on solanaceous plants (i.e., plants in the nightshade family), most typically tomato and less commonly eggplant, pepper and potato.  These insects can also feed on solanaceous weeds such as horsenettle, jimsonweed and nightshade.

Appearance:  You can easily identify hornworms by their blue-green color and large size.  When fully grown, hornworm caterpillars (larvae) can be up to four inches in length and easily seen.  However, smaller hornworm larvae, due to their color, tend to blend in with plant leaves and can be difficult to detect.  Tobacco hornworms and tomato hornworms have seven or eight diagonal white stripes, respectively, on each side of their bodies.  A large red or black horn-like spine protrudes from the posterior (rear) end of caterpillars, giving rise to the name “hornworm”.  Adult hornworms are large, heavy-bodied hawkmoths with a wingspan of up to five inches.  Adults are often mistaken for hummingbirds due to their large size, rapid wingbeats and quick movements.

A tobacco hornworm.
A tobacco hornworm.  Note the reddish spine (horn) protruding from the insect’s rear.

Symptoms and Effects:  Hornworm larvae primarily feed on tomato leaves but occasionally feed on green fruit.  Hornworm larvae can devour up to four times their weight in leaves and fruit each day.  If left unchecked, they can defoliate a tomato plant.  In addition, hornworm-damaged fruit often decay on the vine before harvest, or they may not rot but end up with dry feeding scars that make them unusable.

Adult hornworms/hawkmoths feed on nectar and do not harm plants.

Life Cycle:  Tomato hornworms overwinter as pupae in the soil.  Adults emerge in late June and lay pale-green, spherical eggs on the undersurface of tomato leaves.  Once eggs hatch, larvae immediately begin feeding, and they feed continually for approximately one month.  Larvae eventually drop from plants to pupate (i.e., transform from larvae into moths).  In the upper Midwest, up to two generations of hornworms can occur per year.

Control:  Hornworms rarely cause enough damage to warrant the use of insecticides in home gardens and smaller commercial plantings.  In these settings, frequently monitor tomatoes for hornworm larvae from early July through August, and hand pick the larvae from plants as needed.  Till the soil after harvest to destroy any burrowing larvae that are attempting to pupate.  Tillage can kill up to 90% of larvae in the soil.

A tobacco hornworm covered with eggs of a parasitic brachonid wasp. (Photo courtesy of Deb Zaring)
A tobacco hornworm covered with eggs of a parasitic brachonid wasp. (Photo courtesy of Deb Zaring)

Natural control of hornworms can also occur.  Insects such as lady beetles, green lacewings and some predatory wasps eat hornworm eggs and smaller larvae.  Another wasp (called the Trichogammid wasp) kills hornworms by parasitizing their eggs.  Yet another wasp (called the Brachonid wasp) lays its eggs on larger hornworm caterpillars.  The larvae of this wasp feed inside the caterpillars and kill them.  If you see parasitized hornworms on your tomatoes, DO NOT remove them.  They will produce more wasps that can lay eggs on and kill other hornworms.

If you are a tomato grower with a large acreage of tomatoes, monitor your tomatoes and treat with insecticides if you find an average of more than two hornworms per plant.  Hornworm infestations are often localized and spot treatments will usually take care of any problem.  Apply products for hornworm control when larvae are small; larger larvae are more difficult to control.  There are several insecticides available to control hornworms.  Refer to the University of Wisconsin-Extension publication Commercial Vegetable Production in Wisconsin (A3422) for a full list of insecticides and recommendations.

For more information on hornworms:  See UW-Extension Bulletin A3422, or contact your county Extension agent.

Professional Guide to Emerald Ash Borer Insecticide Treatments – Pest Alert

Emerald ash borer insecticide treatment considerations.  

A variety of insecticide products and application methods are available to professionals for control of the emerald ash borer (EAB).  Since the presence and infestation level of EAB is quite difficult to determine at early stages of an infestation, insecticide treatments may be merited to mitigate damage by EAB.  However, not all ash trees should be treated as some may be too extensively compromised or in poor condition to receive treatment.  Due to the expense of yearly insecticide treatments, one should consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments.  In addition, consider the health of each tree before treating.  Research suggests that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning.  Insecticide treatments are not suggested for trees with greater than 50% canopy thinning.  Ash trees with greater than 50% canopy thinning should be removed and destroyed in accordance with established state and federal guidelines.  For additional information on this topic, see University of Wisconsin Garden Pest Alert XHT1215, Is My Ash Tree Worth Treating for Emerald Ash Borer.

Emerald ash borer insecticide treatment options. 

Insecticide products that are available for use by professionals, with information on appropriate application methods and application timings, are summarized in Table 1.  These products include:

  • Ace-Jet (acephate)
  • ACECAP Systemic Insecticide Tree Implants (acephate)
  • ArborMectin (emamectin benzoate)
  • AzaGuard (azadirachtin)
  • Boxer Insecticide-Miticide (emamectin benzoate)
  • Brandt enTREE EB (emamectin benzoate)
  • Dinocide, Dinocide HP (dinotefuran)
  • IMA-jet, IMA-jet 10 (imidacloprid)
  • Imicide, Imicide HP (imidacloprid)
  • Inject-A-Cide B (bidrin)
  • Mectinite (emamectin benzoate)
  • Merit 2F, Merit 75 WP, Merit 75 WSP (imidacloprid)
  • OnyxPro (bifenthrin)
  • Pointer (imidacloprid)
  • Safari (dinotefuran)
  • Tempo (cyfluthrin)
  • Transtect (dinotefuran)
  • Tree-äge, Tree-äge G4 (emamectin benzoate)
  • Treeazin (azadirachtin)
  • TreeMec Inject (emamectin benzoate)
  • Xytect 2F, Xytect 75 WSP, Xytect 10% infusible (imidacloprid)

University research indicates that soil drenches or injections of imidacloprid provide excellent EAB protection for small ash trees [less than six inches diameter at breast height (DBH)] in the first year following treatment.  Larger trees may require two consecutive years of treatment before they are effectively protected.  Thus, treatment of large trees should begin before the trees become infested.  While spring and/or fall applications are allowed on certain product labels, recent university research has indicated that spring applications have been more effective at controlling EAB and protecting canopy health.  Most insecticide treatments must be repeated each year.  Products containing emamectin benzoate are labeled to provide two years of protection.  Recent university research suggests that some of these products may provide more than three years of control with a single application when used at the highest labeled rate.

Trunk injections and implants require physically drilling or coring into a tree during the application of the insecticide.  Thus, use of these application methods has the potential to cause injury to trees (especially smaller trees), and may provide entry points for certain disease-causing fungi [e.g., Nectria, the cause of Nectria canker (see University of Wisconsin Garden Facts XHT1094 Nectria Canker)]

Table 1.  EAB insecticide treatments available to professionals*
Active Ingredient Product(s) Timing Application Method
Acephate ACE-Jet Mid-May to mid-June Trunk Injection
Acecap Implants Trunk Implant
Azadirachtin AzaGuard, Treeazin Early/mid-April to
early September
Trunk Injection
Bidrin Inject-A-Cide B Inject when infestation is evident Trunk injection
Bifenthrin OnyxPro Apply prior to or just at the time of adult emerge. Multiple applications may be needed Preventative bark and foliage cover sprays
Cyfluthrin Tempo
Dinotefuran Dinocide, Dinocide HP Late-April to late-May Trunk injection
Safari, Transtect, Zylam Soil drench, trunk spray
Emamectin benzoate ArborMectin, Boxer, Brandt enTREE EB, Mectinite, Tree-äge, Tree-äge G4, Tree-äge R10, TreeMec April to September Trunk injection
Imidacloprid Merit 75 WP, Merit 75 WSP, Merit 2F, Xytect 2F, Xytect 75WSP, and others Mid-April to late-May


Early-Sept. to mid-October

Soil injection or drench
IMA-jet, IMA-jet 10, Imicide, Imicide HP, Pointer, Xytect 10% Mid-April to mid-May Trunk injection

The University of Wisconsin does not endorse any one specific commercially available insecticide.  Products discussed in this fact sheet have been evaluated in a variety of university research tests on EAB (  No matter which insecticide you use, always read and follow all label instructions.  Avoid skin contact with insecticides and safely store insecticides out of the reach of children.

For more information on controlling emerald ash borer: 


Viburnum Leaf Beetle – Pest Alert

The viburnum leaf beetle (VLB), Pyrrhalta viburni, is an invasive insect that feeds exclusively on and can significantly damage Viburnum species.  VLB is native to Europe and was detected in Canada in 1947.  The first report of VLB in the United States was in New York State in 1996.  VLB is now found scattered across much of the northeastern US.  In Wisconsin, an isolated infestation of VLB was discovered in Dane County in 2009, but was successfully eradicated.  In 2014, VLB was detected on a mature viburnum bush in northern Milwaukee County and other nearby infestations were detected in June 2015.  At present, VLB infestations are known from Dane, Iron, Kenosha, Milwaukee, Ozaukee, Racine, Walworth, Washington, Waukesha, and Winnebago Counties.

Viburnum leaf beetles adults (left) and larvae (right). (Photos courtesy of Paul Weston, Cornell University,

Appearance: Adult VLB’s are approximately ¼ inch long and yellowish-brown in color. VLB larvae can be up to ⅓ inch long and range in color from yellowish-green to light brown with a series of black spots and dashes on their bodies.

Symptoms and Effects: VLB larvae chew holes in viburnum leaves in the spring creating a lace-like (i.e., skeletonized) pattern.  VLB larvae feed individually or in small groups and can cause significant damage to viburnum shrubs.  This damage can resemble the feeding damage of Japanese beetles (see University of Wisconsin Garden Facts XHT1062 “Japanese Beetle”).  In late June and early July, VLB adults begin to feed, chewing oblong holes in leaves.  Severe VLB infestations can cause complete defoliation of a viburnum shrub, which weakens the plant over time and can eventually lead to death.

Life Cycle: There is only one generation of VLB per year.  VLB’s overwinter as eggs and development from eggs to adults takes approximately eight weeks.  Larvae typically appear in early to mid-May and feed for several weeks, passing through three stages (instars) as they grow.  In early to mid-June, larvae pupate in the soil and adults emerge by late June or early July.  VLB females lay eggs during the summer and into October.  They chew small pits in twigs, deposit five to eight eggs into each pit, and then cover the pits with tiny pieces of chewed wood to protect the eggs.  Each female can deposit up to 500 eggs.  Eggs remain in place through the winter until they hatch the following spring.


Cultural:  When selecting viburnum plants for the landscape, DO NOT use arrowwood viburnum (Viburnum dentatum), European cranberrybush viburnum (Viburnum opulus), or American cranberrybush viburnum (Viburnum opulus var. americanum) as these types of viburnums are strongly preferred by VLB.  Instead use resistant viburnums such as doublefile viburnum (Viburnum plicatum f. tomentosum), Judd viburnum (Viburnum x juddii), or Koreanspice viburnum (Viburnum carlesii).  In addition, between October and the following spring, examine viburnums for twigs where VLB’s have laid their eggs.  Prune and destroy these twigs to reduce VLB numbers.  During the growing season encourage natural VLB predators in your area (e.g., lady beetles, spined soldier bugs, assassin bugs, green lacewings) that can reduce VLB numbers.

Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine;
Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine;

Chemical:  Prior to bud break, apply horticultural oil to twigs where VLB eggs have been laid.  This will significantly reduce the number of eggs that will hatch.  Control any surviving larvae with contact insecticides such as acephate, bifenthrin, carbaryl, cyfluthrin, deltamethrin, lambda-cyhalothrin, and permethrin.  Horticultural oil, insecticidal soap, pyrethrins and spinosad can also be effective.  To achieve the best results, apply insecticides when larvae are small and before they have caused significant damage.  VLB adults can be managed with contact insecticides, if needed, but are mobile and more challenging to control.  Systemic products (e.g., clothianidin and imidacloprid) applied as soil drenches can also be effective, but apply these products after flowering (to minimize any risks to pollinators), but before VLB damage occurs to achieve the best protection.

For more information on viburnum leaf beetle: Contact your county Extension agent.

Squash Bug

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 home gardens and commercial fields alike.  Squash bugs feed on all vine crops, but pumpkins and squash are their preferred hosts, followed by gourds and melons.

A squash bug adult with a cluster of eggs (left) and squash bug larvae with eggs (right). Photos courtesy of Whitney Cranshaw, Colorado State University (left photo) and PJ Liesch, University of Wisconsin-Madison (right photo).
A squash bug adult with a cluster of eggs (left) and squash bug larvae with eggs (right). Photos courtesy of Whitney Cranshaw, Colorado State University (left photo) and PJ Liesch, University of Wisconsin-Madison (right photo).

Adult squash bugs, which often congregate in large numbers, are 1/2 to 3/4 inches long, mottled brownish-black and flattish.  They give off a strong odor when crushed.  Immature squash bugs (nymphs) initially have red heads and legs with whitish-green bodies.  Later they develop black heads and legs with gray bodies.  Squash bug eggs are 1/16 inches in diameter and reddish-orange to brown in color.  They are laid in clusters on the undersides of leaves along the center vein.

 Symptoms and Effects:  Adult and immature squash bugs feed on plant juices and release toxins into leaves.  Early symptoms of an infestation include yellow spotting on the leaves.  Leaves may eventually become dry and brown or black along the edges.  Feeding can also cause wilting which may appear similar to bacterial wilt [see University of Wisconsin Garden Facts XHT1229 (Bacterial Wilt of Cucurbits) for details].  Young plants are more susceptible to severe damage.  Later in the season, adults will also feed on fruit, which may stop developing and begin to rot.

 Life Cycle:  Adult squash bugs overwinter in Wisconsin in protected areas (e.g., in stacks of firewood, in wooded areas or along fence rows).  Adults mate after they emerge in the spring and females lay eggs in late June and early July when vine crops begin to develop.  Eggs hatch after about 10 days.  Nymphs undergo five molts over a period of four to six weeks before reaching maturity.  New adults appear in late July and early August.  There is only one generation of squash bugs per year, but because females lay eggs over an extended period of time, all life stages may be present on plants at once.

Scouting:  The key to managing squash bugs is early detection.  Although it is unusual to find large populations of squash bugs early in the season, be sure to check transplants and new seedlings for adults.  Squash bugs tend to hide on the undersides of leaves where they are protected and may be difficult to find and control.  A degree day model [see University of Wisconsin Garden Facts XHT1086 (Degree Day Calculation) for details] can be used to predict the development of squash bugs.  Using a base temperature of 58°F, eggs will appear at 193 degree days (DD) and nymphs will emerge at 554 DD.  Inspect the undersides of leaves for squash bug eggs beginning in early July.

When to Scout for Squash Bugs
July August September
Early Mid Late Early Mid Late Early Mid Late


CulturalDestroy plant debris from your garden or production field in the fall to reduce the number of overwintering adults.  Burn, bury or hot compost these materials.  Destroying plant debris from areas adjacent to your garden or production field can also help limit squash bug overwintering.  Use crop rotation [see University of Wisconsin Garden Facts XHT1210 (Using Crop Rotation in the Vegetable Garden) for details] to reduce the likelihood of a future infestation.  Consider trellising vine crops where possible, as trellised plants are less susceptible to squash bug infestations.  In smaller plantings, place boards on the ground near vine crops.  Squash bugs will congregate at night under the boards and can then be collected each morning and killed by dropping them into a bucket of soapy water.

ChemicalWhen plants are in the seedling stage, treat if plants are visibly wilting and squash bugs are present.  In older plants, the threshold for treating for squash bugs is one egg mass per plant during the period of when plants are flowering.  Apply foliar applications of registered insecticides when eggs are hatching to target nymphs, which are more easily controlled by insecticides than adults.  See Commercial Vegetable Production in Wisconsin (Extension Bulletin A3422, available at for a complete listing of products.  Note that not all of the listed products may be available for use in home gardens.

For more information on squash bugs:  See Extension Bulletin A3422 (Commercial Vegetable Production in Wisconsin) or contact your county Extension agent.

Asparagus Beetles

The common asparagus beetle (Criocercis asparagi) and spotted asparagus beetle (Crioceris duodecimpunctata) are annual pests of asparagus in Wisconsin.  The common asparagus beetle is the more prevalent of the two insects and the only one that consistently causes economic damage to asparagus.

Common asparagus beetle adult (left) and spotted asparagus beetle adult (right). Photos courtesy of Karen Delahaut
Common asparagus beetle adult (left) and spotted asparagus beetle adult (right). Photos courtesy of Karen Delahaut

Appearance:  Adults of both the common and spotted asparagus beetle have slim, elongated bodies with hard wing covers and are approximately ¼ inch in size.  The common asparagus beetle is bluish-brown with cream-colored spots, while the spotted asparagus beetle is orange with black spots.  Eggs of both species are 1/8 inch long, shiny, dark, and rod-shaped.  Eggs of the common asparagus beetle are laid in groups and are oriented in rows, whereas eggs of the spotted asparagus beetle are laid singly.  Larvae of both species resemble slugs and are plump, wrinkled, and have visible legs.  Larvae of common asparagus beetles have a cream to grey color with dark heads and legs, whereas those of the spotted asparagus beetle have orange bodies.

Symptoms and Effects:  Both adult and larval asparagus beetles can cause direct plant damage and/or a reduction in asparagus spear quality.  Common asparagus beetles typically feed on asparagus spears and ferns (leaves).  Spotted asparagus beetles more commonly feed on asparagus berries.  Feeding on spears causes browning, scarring and distorted growth, rendering the spears unmarketable.  The presence of eggs, as well as insect feces (a black fluid), on the spears also reduces marketability.  Later season feeding on ferns, particularly if asparagus beetle populations are high can lead to defoliation that will reduce yield in subsequent years.

Life Cycle:  Both common and spotted asparagus beetles overwinter as adults in plant debris or mulch.  Adults become active as asparagus plants emerge in early May.  In general, common asparagus beetles become active earlier in May than spotted asparagus beetles (which often do not appear until late May).  Common asparagus beetles lay eggs on emerging asparagus spears, while spotted asparagus beetles lay eggs on ferns.  Eggs hatch approximately one week after they are laid.  Larvae feed for approximately two weeks before they pupate in the soil and new adults emerge from pupae after approximately one week.  Two to three generations of both species of asparagus beetle can occur in a single growing season.

Scouting Suggestions:  Start watching for asparagus beetles in early spring and continue to monitor throughout the growing season.  Scout in the afternoon when temperatures and sunlight are at their peak and when asparagus beetle adults are most active.  In large asparagus plantings, in spring, examine twenty plants at each of five different locations after spears have emerged from the soil.  In the summer, examine ten plants at each of five different locations.  See scouting thresholds below to help determine the timing of chemical treatments.  Spring scouting is designed to reduce damage to spears while later-season scouting is designed to reduce long-term damage caused by defoliation.

Life Stage Threshold
Adults 5-10% of plants infested
Eggs 2% of spears with eggs
Larva 50-75% of plants infested
Defoliation 10% of plants defoliated


CulturalDestroy crop residue to eliminate overwintering sites for asparagus beetles.  Also consider releasing the tiny parasitic wasp (Tetrastichus asparagi), which is an egg parasitoid of the common asparagus beetle and can reduce populations of this insect by up to 70%.  If asparagus beetle populations are high, try using floating row covers early in spring to prevent damage to spears, but remove them after harvest is complete.

ChemicalIf insecticides are needed to reduce asparagus beetle populations below threshold levels, you do not have to treat an entire planting.  You can spot treat areas where threshold levels have been exceeded.  Keep in mind that new plantings tolerate less injury than established plantings and may require more intensive chemical management.  See the University of Wisconsin-Madison Division of Extension bulletin A3422 (Commercial Vegetable Production in Wisconsin), available at, for detailed insecticide recommendations.

For more information on asparagus beetles:  See UW-Extension Bulletin A3422 (available at, or contact your county Extension agent.