Insect Diagnostic Laboratory

 

Damage occurs when the caterpillars tie honey locust leaflets together and feed on the foliage inside the tightly compressed, protective webs.  Affected foliage gradually turns brown.  There are two generations of caterpillars per year.  Extensive damage is most obvious following the second generation in August.

Damage from the mimosa webworm is seldom serious to otherwise healthy, well-established trees.  The webs and browned foliage are unsightly and caterpillar silk hanging from the trees may be annoying.  The damage is more aesthetic than serious.

Chemical control for mimosa webworm is rarely warranted.  A treatment after foliage has turned brown is ineffective and a waste of time.  Such late treatments may do more harm than good by destroying the natural enemies of the pest rather than the pest itself.  Sprays must be applied at the start of the caterpillar period and before webbing is apparent to be effective (mid-June and again in early August).  Insecticides available to homeowners include (e.g., Dipel), Sevin, permethrin, bifenthrin, cyfluthrin, deltamethrin, fluvalinate, lambda-cyhalothrin and spinosad.  Read and follow directions on the insecticide label.

From mid-July through the end of the summer fall webworm caterpillars construct loose, gray, silken webs on the ends of the branches on walnut and other hardwood trees.  We always have a few fall webworms, but reports and observations indicate there will be more than usual this year.

Fall webworm tents start small, but the yellow, hairy caterpillars enlarge the web every few days as they grow and consume the leaves within the tent.  By the end of the summer webs may be 2 to 3 feet long and enclose the entire end of a branch.  The old gray webs hang on the trees most of the winter.

 

Although the fall webworm has been recorded feeding on more than 200 species of deciduous trees and shrubs, the favored host in Iowa is the black walnut tree.  Tents are particularly common on walnut trees growing in the open or on trees at the edge of the woodland.

Damage caused by the fall webworm is not significant to well-established, otherwise healthy trees.  Damage is more unsightly than serious because of the limited amount of foliage consumed and the time of the year.  Trees are not killed by this pest and control is not essential.  Applications of insecticide are of little or no benefit and should be avoided in order to preserve predators, parasites and other biological control organisms.  To be effective sprays must be applied early in the season and with sufficient pressure to penetrate the silk web and reach the leaves within.

The only practical control is to cut off webs when they are first noticed.  Prune and discard the webs you can reach and ignore the rest.  Because caterpillars remain in the tent, time of day is not important.  

The bagworm has historically been an occasional pest on evergreen and deciduous trees and shrubs in southern Iowa.  Infestations have been increasing in number and severity during the past few years, possibly because this Southern pest has benefited from our recent mild winters.  Bagworms are still rare north of Interstate Highway 80.

The most noticeable sign of a bagworm infestation is the presence of tough silken bags on the branches or foliage.  Each caterpillar produces an individual protective silken bag or case around its body.  With its head and legs free, it is able to move about the plant as it feeds on the foliage.  As the larva grows it increases the size of its bag and incorporates into it bits of twigs and leaves for strength and camouflage protection.  The larva will spend its entire life within its bag.  Larvae first appear about mid-June and are full grown by mid-August.  Bags of mature larvae are approximately 2 inches long.

 

Large larvae are difficult to control with insecticide sprays and late sprays after the beginning of August do little to protect the foliage on the tree.  Evaluate carefully if larvae are still feeding before deciding to spray.  Insecticides that can be used against the bagworm include Bt (Bacillus thuringiensis), Sevin, permethrin, Orthene, or malathion.  Apply according to label directions.

The tomato hornworm is one of our best known garden pests. It’s almost as big around as your thumb and can be 4 to 5 inches long. It’s bright green and has a hornlike hook at one end that can be either red or green depending on which of the two species you have on your plant.  After feeding, hornworms move to the soil where they pupate and spend the winter.  The following summer the pupae transform into five-spotted hawk moths and start the cycle over.

 

Tomato hornworms feed on the leaves and fruit of tomatoes and other vegetables including eggplant, potatoes and peppers. They can quickly defoliate portions of the plant, reduce its productivity, and heavily scar the fruit. Toward the end of the summer when the caterpillars are fully grown, it seems they can eat about a leaf an hour!

The first control option is to pick the caterpillars off your plant by hand. They won’t hurt you but the challenge is that they are well camouflaged. They are the same color as the foliage so it will take some hunting to find them when they are small. When they are big, they will be easier to find but then that means they will have grown and developed by feeding on your tomato foliage already!

Another control option is to use a biological insecticide known as Bacillus Thuringiensis or Bt or a synthetic home garden insecticide available in local garden centers.  Be sure to follow label directions.

 

The cicada killer wasp is the largest wasp found in Iowa. They may be up to 2 inches long and are black with yellow markings on the thorax and abdomen and they have rusty colored wings. 

The cicada killer wasp and other digger wasps are solitary wasps; that is, they live independently rather than in colonies and do not depend on other members of a colony to share in the raising of young or the maintaining of a nest. 

The female cicada killer wasps capture annual cicadas in July and August and place them in cells located at the ends of tunnels they have dug in the ground. Each tunnel is about the size of a quarter and extends 24 inches or more into the ground. One or two paralyzed cicadas are placed in each cell, and a single egg deposited before the cell is closed by the female, who flies away, never to return. The wasp grubs feed on the cicadas and develop into wasps that emerge the following summer.

The cicada killer, like other solitary wasps, has the capability to sting, but won't unless handled or threatened. Only female wasps have the ability to sting. Stings inflicted by solitary wasps are usually not severe but reaction varies with each individual.

Wasps are generally beneficial and a nest in an out of the way location where it is not likely to be disturbed should be left alone. If, however, a nest is located where problems could arise, such as under a deck or near an often used door, removal is justified. Ground nests of cicada killers and other digger wasps can be destroyed by placing an outdoor use insecticide dust into the nest entrance during the night. The dust particles will adhere to the wasps as they come and go from the nest. Cover the nest opening with a shovelful of soil after all activity has stopped.

The Japanese beetle is considered the worst pest of turfgrass and landscapes in the United States because they attack so many different types of plants.  The  adult beetles eat the foliage, fruits and flowers of over 300 different plants.  The larvae are white grubs in the soil from August until June where they feed on plant roots (especially turfgrass) and organic matter.

Adult beetles are about 3/8 inch long and 1/4 inch wide.  The head and thorax are shiny metallic green, and the wing covers are coppery red.  The row of five tufts of white hairs on each side of the abdomen is a distinguishing feature.

Control of adult beetles is difficult because they emerge every day for a period of several weeks, beginning in late June.  Handpicking or screening or high-value plants may be of benefit in isolated situations with limited numbers of beetles.  Spot spraying infested foliage of high value plants with carbaryl (Sevin), permethrin (Eight) or cyfluthrin (Tempo) may reduce damage for several days, but multiple applications are required to maintain control.  Spraying the adult stage is not an effective strategy for prevention of white grubs.

JB has been reported from 19 different counties in Iowa since 1994, predominantly in the east-central region of the state.  Please let us know if you find JB in a county where they have not already been reported:  Black Hawk, Boone, Clayton, Clinton, Dallas, Dubuque, Floyd, Jackson, Johnson, Lee, Linn, Madison, Marshall, Muscatine, Page, Polk, Scott, Story, Woodbury.

 

 

The imported longhorned weevil and the strawberry root weevil are common "accidental invaders" that crawl into houses and buildings from outdoors by mistake during late June and July. The weevils are harmless; they do not damage the house or furnishings; they can not bite or sting people or pets. They are merely a nuisance by their presence.

The larvae of these weevils live in the soil and feed on the small roots of many different plants, including aster, clover and turfgrass. They do not cause apparent damage to the plants and control of the larvae in the soil is not practical nor necessary.

Some of the invasion by longhorned weevils can be prevented by exclusion techniques that close their routes of entry. Look for and seal cracks and gaps through which the adults can crawl into the building. Spraying a residual insecticide labeled for beetle control outdoors on and along the foundation and in outdoor areas of weevil abundance may be of some benefit. Fro more information on insecticides please see "Insecticides in the Home Landscape and Garden."

Adults already inside need only be vacuumed or swept up and discarded. Household aerosol insecticides are not very effective for controlling these weevils.