Category Archives: Insect

Two-Lined Chestnut Borer

The most important insect cause of oak mortality is the two-lined chestnut borer (Agrilus bilineatus). This insect is attracted to stressed and weakened oaks. Environmental extremes (e.g., drought), construction injury to roots, soil compaction, road salt injury, defoliation by leaf-feeding insects, storm damage and weakening from disease are all stresses that predispose trees to two-lined chestnut borer attack.

Two-lined chestnut borer galleries.
Two-lined chestnut borer galleries.

Appearance: Adult two-lined chestnut borers are elongated, greenish-black metallic wood boring beetles that are about 1/5 to 1/2 inch in length. They have two yellow stripes along their backs. Larvae are slender, legless and white, and have a small, flattened area behind their heads.

Symptoms and Effects: Two-lined chestnut borers attack many types of oaks, including red, black, white and bur oaks. Symptoms include dieback at the end of branches, sparse, small or discolored foliage, or leaves that wilt suddenly, turn uniformly brown and typically remain attached to the branches.

Leaf browning, and twig and branch death occur when two-lined chestnut border larvae feed under the bark and destroy the nutrient and water conducting tissues (i.e., the phloem and xylem). This girdles and kills the branches above the point of feeding. Death of a tree due to a two-lined chestnut borer infestation may take from one to five years. To confirm chestnut borer activity, peel away the bark on dead or dying branches or trunks. Look for slender, whitish larvae and thin, random, feeding galleries (trails) under the bark.

Life Cycle: Two-lined chestnut borers overwinter as larvae and pupae in infested trees. Adult beetles emerge from trees through D-shaped holes in late May and are active until early July. Eggs are inserted into bark crevices and hatch in one to two weeks. Larvae feed in cambial tissue and cut off the vessels that transport food and water in the tree. There is one generation of two-lined chestnut borer per year.

Control: The best defense against two-lined chestnut borer is prevention. Healthy, non-stressed trees will not attract two-lined chestnut borer adults, and vigorous trees are able to fight off invading borers. Water oaks (approximately one inch of water per week) during dry periods to minimize drought stress. Avoid compacting soil, or changing the soil grade or water drainage pattern during construction. Also avoid damaging the bark; or allowing significant defoliation by insects such as gypsy moth, canker worm, or forest tent caterpillar. Remove and dispose of any two-lined chestnut borer-infested wood before beetles emerge in mid-May. Cover all oak woodpiles with plastic tarps from mid-May through mid-July to limit borer movement. Systemic insecticides that are applied to trees by drenching or injection (e.g., those containing imidacloprid) can also be used for control. These products are best applied by a professional arborist. Trees with significant dieback will be difficult to save.

For more information on two-lined chestnut borer: See UW-Extension bulletin A2902 or contact your county Extension agent.

Thrips in Greenhouses, Managing

Western flower thrips, Frankliniella occidentalis, are likely the most serious pest of greenhouse crops in the world. Thrips have spread throughout the horticulture industry on plugs, cuttings, and small plants. Because of thrips’ small size (116 inch) and tendency to remain hidden in flower buds, they are difficult to detect before severe feeding damage is evident. Thrips cause damage to greenhouse crop in several ways: directly by their feeding and egg laying activities on plants, and indirectly by acting as vectors for tospoviruses.

Western flower thrips adult. (Photo courtesy of L. Lindquist, OARDC.)
Western flower thrips adult. (Photo courtesy of L. Lindquist, OARDC.)

Plants Attacked and Damage: Thrips have a relatively broad host range, feeding on greenhouse crops such as carnation, chrysanthemum, fuchsia, geraniums, hibiscus, impatiens, ivy, marigolds, petunia, roses, and verbena. Thrips feed by piercing plant cells with their mouthparts and feeding on the exuded plant juices. The collapse of plant cells due to feeding often results in deformed flowers, leaves, and shoots. Silvery flecked scars or small black “fecal” spots also may be seen on the expanded leaves. In addition to direct feeding damage, thrips may cause indirect damage by vectoring (spreading) two closely related tospoviruses (impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV)) to uninfected plants. These tospoviruses have wide host ranges, affecting over 600 plant species in 62 families. Growers of begonia, cineraria, cyclamen, exacum, gloxinia, impatiens, New Guinea impatiens, primula, and ranunculus have experienced substantial losses due to these viruses. Young plants can be especially susceptible to infection and there is no cure once infection has occurred. Immediate roguing of infected plants should be combined with strict thrips management to prevent serious losses.

Life Cycle and Biology: Most thrips in greenhouses are females. Adult females live for approximately 30-45 days and lay 150-300 eggs that are inserted into plant tissue. Eggs can be laid on the upper or lower leaf surface, depending upon the plant species, and thus, targeting pesticide applications to the area when and where thrips are located is important. The first two thrips larval stages remain protected in the tender young plant tissue. Eventually, second instar larvae stop feeding and drop into the soil or other growth medium to pupate (transform into the adult). Adults emerge two to five days later, depending on temperature.

The thrips life cycle is dependent on temperature, with development occurring between 50 and 90°F. Thrips can survive temperatures below 50°F. However, they do not develop at this temperature. The thrips life cycle vary in length from seven to 14 days at fluctuating temperatures between 68-98°F that are common in most greenhouses.

Control: The most effective thrips management strategy is to prevent thrips form entering greenhouses. Monitor for adult and larval thrips as soon as young plants or cuttings are received. When possible, keep thrips-infested plants isolated in a separate area to avoid spread. Although winged adults are relatively weak fliers, they can be carried on air currents or on employees’ clothing. Consider worker movements to and from highly infested greenhouses, and avoid wearing clothing with colors (e.g., pink, blue, yellow, white, or green) that are attractive to thrips.

Thrips injury on petunia, an indicator plant for WFT and virus. (Photo by L. Lindquist, OARDC.)
Thrips injury on petunia, an indicator plant for WFT and virus. (Photo by L. Lindquist, OARDC.)

Both chemical and biological control strategies are available for thrips control. However the bottom line is that there are no easy answers for thrips management. Chemical control of thrips is difficult because thrips tend to hide in flowers and buds, they have a rapid life cycle with a high reproductive rate, they have a wide host range including many weed species, and there is widespread resistance to numerous chemical control products. When applying insecticides for thrips control, use a droplet size that is less than 100 microns in diameter to attain more effective contact. Also, apply insecticides every two to three weeks before peak thrips activity to ensure control of adults before they begin to lay eggs. The interval between applications may vary between three and seven days depending on the temperature, relative numbers, and stage of the crop. When selecting control materials, rotate between classes of insecticides to help delay the development of resistance. Research suggests using a material or a combination of materials for one generation (two to three weeks), then switching to an insecticide in another class. There is no single pesticide that will provide total thrips control. Abamectin and methiocarb are the most effective control products registered for thrips. Other products that provide some control are azadirachtin, cyfluthrin, acephate, endosulfan, and fenoxycarb. Tank mixes of abamectin, azadirachtin followed by a fenoxycarb spray have provided good control.

The use of biological controls (natural enemies) against thrips has been used in greenhouse vegetable production. The potential exists for biological control to be part of an IPM strategy for thrips control in ornamentals. To be successful, become familiar with thrips monitoring, and the use of environmentally friendly or “softer” control products such as botanicals and insect growth regulators (IGR’s).

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

Thanks to Phil Pellitteri and Lis Friemoth for reviewing this document.

Squash Vine Borer

The squash vine borer (Melittia cucurbitae) is an annual pest of pumpkins and squash. This insect is often not recognized as a potential pest, but can be economically important in some years. Winter squash is highly susceptible to attack.

A squash borer larva in a vine (left) and an adult squash borer (right).
A squash borer larva in a vine (left) and an adult squash borer (right).

Appearance: The adult squash vine borer is a day-flying clearwing moth that resembles a wasp. The forewings of the moth are greenish-brown while the hindwings are transparent with a fringe of reddish-brown hairs. The wingspan of the insect is 114 to 112 inches. The moth’s body is rusty orange with black bands on the abdomen. Borers are wrinkled and white with brown head capsules. Larvae are 112 to two inches long at maturity.

Symptoms and Effects: Damage caused by squash vine borer larvae often goes undetected until infested plants wilt and die in late July and August. The first symptom of feeding damage is when plants wilt midday. This wilting is caused by larvae as they tunnel through vines and destroy the tissue that transports water. Wilt symptoms may be confused with those caused by bacterial wilt or Fusarium wilt. To distinguish between squash vine borer injury and these diseases, look for entrance holes near the base of wilting vines. If frass (i.e., feces) is present near the entrance holes, split the stem lengthwise to confirm the presence of larvae. Fields that have been damaged in the past are likely to be damaged again.

Life Cycle: Squash vine borers overwinter as pupae in the soil. They emerge as moths in late June and July, when 900 DD50 have been reached. This coincides with full bloom of the common roadside weed chicory. Female moths lay small, brown eggs at the base of plants. Once the eggs hatch seven to 10 days later, the larvae immediately begin burrowing into vines where they feed for 14 to 30 days. As larvae feed they leave behind a characteristic light brown frass (i.e., feces) that resembles sawdust. Fully grown larvae leave the plant to pupate. There is one generation per year.

Control: Currently there are no treatment thresholds for the squash vine borer. However, pumpkin and squash plants should be monitored once 900DD50 have accumulated. Larvae boring into a main stem will kill an entire plant, while those boring into a runner will only kill the runners, and not cause economic damage in larger plants. Two to three insecticide treatments, five to seven days apart during the three week egg-laying period around 1000DD50 will control most of the larval borers before they burrow into vines and become protected by vine tissue. Treat plants with runners that are less than two feet long is particularly important. For a list of pesticides that will control squash vine borers, refer to UWEX publication A3422 “Commercial Vegetable Production in Wisconsin”. Floating row covers may also be used during the flight period of adult squash vine borers to prevent egg-laying on susceptible plants. Keep in mind however that blooming plants need bees to pollinate flowers. Therefore, row covers must be removed during blooming to allow bees access to plants.

For more information on squash vine borers: See UW-Extension Bulletin A3422, or 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 commercial fields and home gardens alike. Squash bugs will feed on all vine crops, but prefer pumpkins and squash, followed by gourds and melons.

An adult squash bug.
An adult squash bug.

Appearance: Adult squash bugs are dark brown mottled with grey, and flattened. When crushed, they give off a disagreeable odor. Squash bug eggs are a metallic bronze color, and are laid in clusters between leaf veins on the lower leaf surface of susceptible plants. Young nymphs are pale green to white, and somewhat resemble aphids in shape. Later instar nymphs are grayish-white with black legs.

Symptoms and Effects: Large numbers of overwintering adults can cause serious stand losses to transplants and seedlings. Squash bugs feed on plant sap, and initially, feeding leads to yellow spotting on leaves. As the damage progresses, the spots become brown and dry. Vine-feeding results in a wilting of the vine from the point of feeding outward. Large numbers of insects can cause entire plants to wilt. Cosmetic damage to developing fruit may occur from adult or nymph feeding making the fruit unmarketable.

 

 

Squash bug nymphs.
Squash bug nymphs.

Life Cycle: There is one generation of squash bugs per year in Wisconsin. Eggs of the squash bug are laid in clusters on the lower leaf surface near leaf veins. The eggs hatch one to two weeks later, in late June to early July. Immature squash bugs undergo five molts before reaching maturity. Adults appear in late July to early August and enter a resting state called diapause, in the fall. These overwintering adults become active in the spring and lay the next season’s eggs. Warm winter weather favors the survival of overwintering adults, increasing the likelihood of outbreaks the subsequent summer.

Control: The key to management of squash bugs is early detection. Even though large populations of squash bugs are not likely to occur early in the season, growers should check their transplants or newly emerged seedlings for the presence of adults. Destroy crop residue in the fall to reduce the number of overwintering adults. Crop rotation will also reduce the incidence of infestation.

When plants are flowering, controls should be implemented when a threshold of more than one egg mass per plant is detected. If not controlled at this time, plant damage and yield loss will result. Check the lower leaf surface for squash bug eggs. Young nymphs are most susceptible to control while adults are more difficult to control. Pyrethroid insecticides such as permethrin are recommended for control. However, these products are less effective when temperatures are above 80°F. Because of their protected location on the lower leaf surface, control of the squash bug may be difficult. In addition, in recent years, squash bugs have developed resistance to some insecticides. Refer to UWEX publication A3422 “Commercial Vegetable Production in Wisconsin” for a list of registered insecticides.

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

Spruce Spider Mite

Spruce spider mites can attack a number of conifers including spruce, hemlock, white cedar (arborvitae), larch, and juniper. These mites go through four to six generations per year and populations can explode under warm, dry conditions.

Spider mite damage.
Spider mite damage.

Spider mites feed by sucking on plant sap. Damage is more common on inner branches and areas protected from direct rain. Infested needles become mottled and appear yellowish to gray in color. Once damaged, needles will not recover even after the mites are gone. Under heavy infestations needles can brown or fall prematurely. Conifers hold needles for up to four years so damage is sometimes found that represents an old infestation. Because other conifer disorders have similar symptoms, the presence of mites or mite eggs is used for diagnosing the problem. Plants should only be treated if mites are active or if large numbers of overwintering eggs are found on shoots.

Spider mite overwintering eggs.
Spider mite overwintering eggs.

Control: First determine if mites still active by shaking branches over a white piece of paper. Mites are only 150 of an inch long, but can be seen walking on a light-colored background. If large numbers of eggs are observed in the fall, plants should be checked in spring for signs of activity. Most insecticides are ineffective against spider mites, and frequent use of insecticides can promote mite outbreaks by killing mite predators. Sprays containing insecticidal soap, horticultural oils or specific miticides (hexthiazox, bifenthrin) are effective controls. Heavy rain will wash mites off of plants and is a form of natural control. Similarly, a forceful stream of water can help reduce mite numbers.

For more information on spruce spider mites: Contact your county Extension agent.

 

Springtails

Springtails are very common, small (1 to 3 mm long), wingless insects that jump or hop using a furcula, a forked structure on the underside of the abdomen that acts like a spring. Most springtails live in rich soils and leaf litter, or in decaying wood, where they feed on organic matter, fungi, or algae. Dark bodied springtails found in late winter are referred to as “snow fleas”. Springtails are harmless, nuisance insects.

For more information on springtails:  Contact your county Extension agent.
Springtails.

Springtails can build up in large numbers and are often seen after soil has been disturbed. They can congregate around house foundations or sidewalks where they can be a temporary annoyance. Springtails also can occur around floor drains, and in damp basements, and crawl spaces. High populations of springtails are temporary and disappear by themselves.

Control: Springtails do not survive the dry conditions found indoors. Therefore, any steps to improve ventilation and promote drying are the best long term solutions to managing this insect. Outdoors, removal of wet leaves, bark mulch or other organic matter will eliminate breeding sites. Landscape and household insecticides or insecticidal soap sprays can be used to treat infestations, but will provide only temporary relief if the favorable breeding sites and conditions for survival are not eliminated. If springtails are migrating indoors check door sweeps, vents and foundation openings and make changes (e.g., replacing worn door sweeps, or caulking holes) that will keep the insects out. When masses of springtails occur, they can be swept or vacuumed up and discarded.

Houseplants with organic matter in the soil can become infested with springtails. Springtails will not harm houseplants, and allowing the soil to dry out will usually eliminate these insects. If needed, plants can be taken outdoors and the soil can be treated with garden insecticides.

For more information on springtails: Contact your county Extension agent.

Spotted Wing Drosophila

Spotted wing Drosophila (SWD), Drosophila suzukii, is an invasive vinegar fly native to Southeast Asia. It became established in Hawaii during the 1980’s, and was first discovered in the continental United States in California in 2008. SWD quickly spread throughout the Pacific Northwest and Canada, and was found in Florida in 2009. At least 45 states have now reported SWD, with Michigan and Wisconsin first reporting the insect in 2010. Breeding populations and fruit infestations in Wisconsin were reported in 2012 and were most severe in fall-bearing raspberries.

SWD males (left) have dark spots at the tip of each wing.  Females (right) lack these spots, but have a serrated egg-laying structure (see insert).
SWD males (left) have dark spots at the tip of each wing. Females (right) lack these spots, but have a serrated egg-laying structure (see insert).

Vinegar flies are part of a large group of insects that typically attack rotting or damaged fruit, but typically do not damage healthy fruit. SWD are similar in size, shape and appearance to other vinegar flies. However, the female SWD has a serrated ovipositor (i.e., an egg-laying structure) that allows her to cut into healthy fruit to lay eggs. Larvae feed within healthy fruit tissue causing tissue collapse within a few days; consequently crop loss can be severe.

SWD damage (clockwise from lower left) on raspberry, blueberry and strawberry.  An SWD larva on a raspberry fruit (lower right).  (Fruit photos courtesy of USDA ARS HCRU-Lee Lab; larva photo courtesy of Phil Pellitteri)
SWD damage (clockwise from lower left) on raspberry, blueberry and strawberry. An SWD larva on a raspberry fruit (lower right). (Fruit photos courtesy of USDA ARS HCRU-Lee Lab; larva photo courtesy of Phil Pellitteri)

Appearance: SWD adults are small, 1/16 to ⅛ inch long with red eyes and a light brown thorax and abdomen. SWD males are identified by a single dark colored spot towards the tip of each wing, as well as two dark colored bands on each foreleg. SWD females do not have these markings and are distinguished from other vinegar flies by their serrated ovipositor (which is only visible with magnification). SWD eggs are tiny and white, and larvae are cream-colored, wormlike, legless, and up to ⅛ inch long.

Host Range: SWD prefers thin-skinned, soft-fleshed fruit and is primarily a pest of berry crops, including brambles (e.g., blackberries and raspberries), strawberries, blueberries, and currants. Grapes and tree fruits (e.g., cherries, peaches, nectarines, plums, and Asian pears) are also hosts for SWD, as are non-edible fruiting plants such as snowberry, pokeweed, dogwood, honeysuckle, or bittersweet nightshade.

Symptoms and Effects: Initial symptoms of an SWD infestation are small scars or slits (left by females during egg-laying) on intact fruits. Soft, sunken spots appear around the scars as larvae begin to feed. Fruits soon collapse and become juicy. Other organisms (e.g., fungi and bacteria) are often introduced during egg-laying and can cause additional fruit deterioration. The effect of SWD on some hosts (e.g., grapes) may vary based on varietal preferences; the effect on other hosts (e.g., brambles) may be complete crop loss.

Life Cycle: SWD prefers moderate temperatures and can complete a generation in as little as eight to nine days. SWD adults live for about two weeks and females can lay more than 300 eggs during this time. Females lay from one to three eggs per fruit and several females can lay eggs in a single fruit. Eggs hatch in as little as one to three days. Larvae can complete feeding within several days (the exact length of time depends on temperature) and can pupate in the damaged fruit or in the top layers of leaf litter around infested plants. Because of their short generation time, large SWD populations can build up, especially if the insect is left uncontrolled.

Homemade SWD traps are easy to make from a 32 ounce clear plastic container with a lid.
Homemade SWD traps are easy to make from a 32 ounce clear plastic container with a lid.

Monitoring: The first and most important step in SWD management is to determine whether SWD is present. Use trapping of adult flies for early SWD detection and to monitor trends in adult populations. Start monitoring when fruits begin to ripen and until harvest is completed. You can buy commercially available traps, or make simple, inexpensive traps using a 32 ounce clear plastic container with a lid. To allow SWD adults to enter the trap, drill or melt ten 3/16 inch diameter holes around the top of the cup. Bait traps with one tablespoon active dry yeast and four tablespoons sugar in twelve ounces of water. Alternatively (although less effective), you can use a two inch layer of apple cider vinegar in the bottom of the container. Add one to two drops of unscented dish soap to the trap to break the surface tension of the liquid so that flies are more likely to drown. Hang traps in a shaded plant canopy where fruit is present. For strawberries, place traps on the ground. Check traps and replace liquid bait weekly, using a hand lens to identify trapped insects. Be careful not to pour bait on the ground near the traps as this will confuse SWD adults and reduce the effectiveness of the traps.

If you suspect fruit are infested with SWD, use a fruit dunk flotation method to look for SWD larvae. Place a random sample of fruit in a sealed plastic bag or glass dish and crush the fruit lightly to break the skin. Add a mixture of ¼ cup of salt in four cups of water and let the fruit, salt and water mixture stand for one hour. Look for larvae that float in the liquid. Backlight the bag or dish to help with detection.

Control: Remove hosts such as wild blackberries, wild raspberries, wild plums, and wild grapes, which can serve as a reservoir for SWD. When growing fruit crops that are preferred hosts for SWD, be sure to harvest fruit promptly, and remove and destroy overripe or infested fruit to help minimize the buildup of SWD. Exclusion netting with a fine mesh or row covers can be used prior to fruit ripening to keep SWD away from fruit. Use traps (as described above) to monitor for the presence of SWD adults. As needed, use broad-spectrum insecticides for control. Products containing carbamates, organophosphates, pyrethroids and spinosyns are available for use in conventional production. Spinosad and pyrethrum are available for use in organic production. Neonicotinoids are not effective against SWD and should not be used. Be sure to choose a product labeled for use on the specific fruit crop that you are growing and make sure to follow all label instructions to ensure that you use the product in the safest, most effective manner possible. Spray thoroughly in the plant canopy to kill adults before they are able to lay eggs in the fruit. Because you are applying insecticides to an edible crop, be especially aware of any pre-harvest interval (PHI) restrictions of the product that you select.

For more information on spotted wing Drosophila: Visit the SWD website at http://labs.russell.wisc.edu/swd/ or contact your county Extension agent.

Sowbugs

Sowbugs and related pillbugs are harmless soil inhabiting creatures that occasionally are found in high numbers in and around the home. These hard-shelled, multi-legged, segmented isopods feed on decaying organic matter in the soil. Sowbugs often collect under flower pots, outdoor rugs, and boards, in leaf litter, and in cool, damp areas such as basements and crawlspaces. Pillbugs roll up into a ball if disturbed.

A sowbug.
A sowbug.

Sowbugs live in the soil and often come out at night and crawl around. When the sun comes up, they look for moist, sheltered sites and often crawl beneath door sweeps, or under siding and fall into the basement. The biggest numbers outdoors are seen in damp areas with ample organic matter such as mulched flower beds, and wooded areas with accu­mulations of leaf litter.

Control: If sowbugs come indoors, they will not survive long because of a lack of moisture. They can be vacuumed or swept up. To prevent sowbugs or pillbugs from coming inside, caulk or seal around door and window frames to eliminate gaps, and especially along the foundation where they often crawl up under siding. Minimize moisture sites (leaky faucets, air conditioners, broken down spouts) and consider removing organic debris such as bark mulch from the foundation as this can serve as a breeding site.

If large numbers of sowbugs and pillbugs migrate indoors, consider applying insecticides outside as a barrier treatment. Granular insecticides, or sprays applied with compressed air or a hose-end sprayer, can be applied in a three to six foot band along the foundation of the structure. Sevin (carbaryl) can be used, but this product is less effective at cooler temperatures. Products containing synthetic pyrethroids such as cyfluthrin, permethrin, bifentrin, and cypermethrin work under cool conditions.

For more information on sowbugs and pillbugs: Contact your county Extension agent.

Sod Webworms in Turf

Sod webworms are highly destructive pests of lawns, and are also important pests of athletic fields, cemeteries, golf courses, and parks. There are numerous species of sod webworms in the United States. However, the two most common species that attack cool-season turfgrass are the bluegrass and the larger, sod webworm. Damage to turf is caused by feeding of the larval, caterpillar or “worm” stage, and damage shows up as small dead patches of grass among healthy grass. Sod webworm caterpillars are relatively small larvae that live in silk-lined tunnels at or near the soil-thatch interface, and damage turf by clipping-off grass blades and shoots with their chewing mouthparts. These caterpillars are cream to gray or green in color with many dark spots spaced evenly over their bodies. Adult sod webworms are small, dull-colored moths that have large snouts and wings that fold close to their bodies.

Sod webworm adult.
Sod webworm adult.
Sod webworm caterpillar.
Sod webworm caterpillar.

 

 

 

 

 

 

 

Plants Attacked and Damage: Adult sod webworm moths do not cause damage to turf. However, sod webworm caterpillars attack and feed on most of the common cool-season turfgrass species, including creeping bentgrass, fine-leaf and tall fescues, Kentucky bluegrass, and perennial ryegrass. Sod webworms prefer sunny sites, south-facing slopes, or areas along sidewalks, where turf is hot and dry. Rarely are shaded turf areas attacked. Damage caused by sod webworms typically first appears in late spring with additional damage occurring in mid to late summer. The most severe damage usually occurs in July and August when temperatures are hot, and grass is experiencing drought stress and is not growing vigorously.

Sod webworm damage usually begins as general thinning of turf, followed by development of small patches of brown, closely-cut grass. A more thorough look reveals silk-lined tunnels in the soil-thatch interface. Green fecal pellets are commonly found near the entrance of a burrow. As feeding damage intensifies, small damaged areas often merge into large irregular patches of brown. Early symptoms of sod webworms may be masked if turf is dormant from drought stress. Consequently, sod webworm damage is often mistaken for heat or drought stress. Turf damaged by sod webworms may be slow to recover without sufficient rainfall or irrigation and fertilization. Symptoms caused by fungal pathogens such as the brown patch pathogen and Fusarium may also be mistaken for sod webworm damage.

Life Cycle: Sod webworms overwinter as partially-grown larvae in silk-lined tunnels in the thatch or soil. Larvae resume feeding in the spring, grow rapidly, pupate (transform into adults), and emerge. Newly emerged adults then mate, and within one day thereafter females start laying eggs. Egg laying typically occurs at or near dusk, and continues for a few hours. Moths usually live for about two weeks, and each female can lay approximately 60 eggs per night and as many as several hundred eggs during her lifetime. Eggs typically hatch in about one week and caterpillars usually complete their development in four to seven weeks. A complete life cycle (egg to adult) typically requires six to 10 weeks. Most species of sod webworms have two to three generations per year depending on geographic latitude.

Control: While most of the common cool-season turfgrass species are susceptible to sod webworm damage, there are improved cultivars of perennial ryegrass that have meaningful resistance. These cultivars should be grown where appropriate.

When growing susceptible turfgrass species, sod webworms are relatively easy to control with insecticides. Chemical controls for sod webworms should be directed towards the caterpillars, and not the adult moths. However, moth flight may be used as an indicator for predicting subsequent caterpillar infestations (10 to 14 days after peak flight) and the optimal time to make a control application. Because most sod webworm caterpillar feeding occurs at night, treatments should be made in the late afternoon or early evening. This management strategy will minimize potential volatilization and photodegradation, as well as potential exposure to humans and animals. Liquid sprays often work more effectively than granules. However, to maximize efficacy when using liquid sprays, turf should not be irrigated or mowed for at least 24 hours. This will ensure that insecticide residues remain on the turf foliage. There are numerous carbamates, organophosphates, and pyrethroids that are labeled for use against sod webworms. There are also two relatively new types of insecticides, halofenozide (an insect growth regulator) and spinosad (a bacterium-based product) that are effective against sod webworm caterpillars.

As an alternative to conventional insecticides, so-called “biorational” products can also be used to control sod webworms. Products like entomopathogenic nematodes, azadirachtin or neem (a botanical insecticide), and products containing Bacillus thuringiensis (Bt) are labeled for use against sod webworms. These products work best against young larvae, and should be applied before sod webworm caterpillars are large enough to cause damage. Biorational products are sensitive to heat and sunlight, thus they should be applied late in the day.

For more information on sod webworms: See UW-Extension Bulletin A3714, or contact your county Extension agent.

Scales

Scales are probably one of the most difficult insects to control because of their protective covering. There are many species of scales, but they can all be categorized as either soft or armored.

Brown salt scale.
Brown salt scale.

Soft scales are tropical insects and are economically more important than armored scales in the greenhouse. They are larger in size than armored scales and the protective shield can’t be separated from the insect body beneath. Soft scales have a wide host range among the bedding and foliage plants. Common greenhouse scale species include the brown soft scale (Coccus hesperidum), hemispherical scale (Saissetia coffeae), and nigra scale (Parasaissetia nigra). Ferns, orchids, schefflera, crossandra, zebra plant, weeping fig, citrus, ivy and holly are the common hosts.

Armored scales, as the name implies, have a hard, waxy shield. They rarely present a problem in greenhouses, but can be a concern in interior plantscapes and conservatories.

Appearance: Female soft scales are what you typically think of when you think of a scale insect. They lack any recognizable body parts and are grey, brown or black and smooth and measure 14 inch in diameter. Young adults are lighter in color, but soon darken as they mature. The adult male scale resembles a tiny pale gnat, but they lack mouthparts and cannot feed. Brown soft scales are oval and flattened and pale in color with a grid-like pattern. Hemispherical scales, in contrast, are circular, convex, shiny, and brown, while the nigra scale can vary in appearance depending on its host.

Symptoms and Effects: Like other members of the order Homoptera, scales feed by sucking plant sap. Some scales inject toxins as the feed, further compounding the damage. Yellowed leaves and distorted foliage are indications of scale infestations. With soft scale infestations, honeydew (a clear, sticky plant sap) and sooty mold are also present.

Life Cycle: Female scales produce 50 to 200 eggs or live young depending on the species. Nymphs emerge from eggs in one to three weeks. The nymph stage is called a crawler and is the only mobile life stage. Upon hatching, they immediately begin their search for a suitable host plant. Nymphs undergo three instars before settling and a hard or waxy covering envelops the females. At this point the female’s body degenerates into a feeding sack beneath the scale cover.

Scale eggs.
Scale eggs.

Scouting Suggestions: Visually inspect the lower leaf surfaces and stems for the presence of scales. Yellowed foliage may indicate that a closer look is warranted. Be sure to inspect all new plant shipments thoroughly for signs of scales. Ants may be present if copious amounts of honeydew have been secreted. Parasitized scales will be darker in color and have one or more holes in the shield.

 

Control:

Non-Chemical: Remove and destroy all heavily infested plants. Wash off honeydew and dislodge crawlers with water sprays. Inspect all new plant material on arrival. There are many natural enemies of soft scale, but few are commercially available for greenhouse use.

For information on biological control, refer to NCR publication 581 “Biological Control of Insects and Other Pests of Greenhouse Crops”.

Chemical: There are several insecticides available for control of scales. Refer to UW-Extension publication A3744 “Insect Pest Management for Greenhouses” for a complete listing of available products. If there are two or more adult scales or a large number of crawlers per leaf, spot treat affected plants. You will need two to three applications at 10 day intervals to effectively control the population. If you are using natural enemies to provide some control of scale outbreaks, avoid the use of broad spectrum insecticides as these will also kill the beneficial insects. The insect growth regulators such as azadirachtin and soaps are very effective at controlling soft scales.

For more information on scales: See UW-Extension Bulletin A3744, or contact your county Extension agent.