Native insect; outbreaks occur at roughly year intervals and usually last 2 to 4 years; most common in forests, especially where aspen is abundant. Exotic pest; severe defoliation during outbreaks can occur for 2 to 3 years in urban and forested areas, especially where oaks are abundant. Tags: forestry , gypsy moth , integrated pest management , lymantria dispar , natural resources , pest management. Deborah McCullough mccullo6 msu.
Spraying a pesticide on the webs is only effective if there is enough spray pressure to penetrate them. Like bagworms, carbaryl or Bacillus thuringiensis can be used. Another difference between fall webworms and Eastern tent caterpillars is their appearance. While webworms tend to be yellow, green or orange with two rows of black spots on their back with long white hairs covering their body, Eastern tent caterpillars are black with a gold or white stripe down their back.
Eastern tent caterpillar webs can be spotted in the late spring to summer and these are formed in the crotch of a tree rather than the end of a branch like the fall webworm.
Common trees Eastern tent caterpillars are found in are wild cherry, crabapple, apple, and occasionally other types. If there is an abundance of caterpillars, they can defoliate an entire tree, but they will seldom be able to kill it. You can save customers the hassle of dealing with these pests by removing and destroying any egg masses you spot before they hatch in the spring. If the caterpillars have already hatched, they too can be easily removed by pulling the web down with a trusty stick and crushing the fallen insects.
Bagworms versus webworms Jill Odom. Fall webworm webs can be found on the ends of tree branches. Bagworms Bagworms disguise themselves on evergreen trees. Spot treatments are ideal, but that option depends on the results of scouting.
Corn with above ground Bt trait s may still be attacked, so check those as well. Pastures, soybeans, alfalfa, and other crops are not immune to damage either, especially with large armyworm populations.
In a lawn, before treating, check the ground and throughout the turf thatch at the lawn edge to see if larvae are present. This is especially important if the lawn borders a grassy area or recently harvested agricultural field. If larvae are found and are only on the edge, spot treating in that area using an insecticide labeled for turf that targets caterpillars should be effective.
If larvae are already throughout the lawn, the entire yard may need to be treated. Both liquid and granular products are available. If the caterpillars are longer than one inch, they are almost done feeding and it is best to let them finish eating and focus on restoring the turf.
Backyard corn plots are also susceptible to damage. Over a period of eight to thirteen years, their populations start to increase until they reach tremendously large numbers.
These outbreaks usually last for about three to four years in Minnesota, although in southern areas of the United States outbreaks have been known to last as long as nine years. Finally, natural controls, including cold or damp spring or early summer weather, starvation, and viral disease, can cause populations to crash to very low numbers.
Populations are also significantly reduced by wasps and flies that parasitize eggs, larvae, and pupae. The most conspicuous of these parasitic insects is a large gray fly, Sarcophaga aldrichi, which is often a nuisance to humans. This fly is native to Minnesota. Their numbers increase in response to forest tent caterpillar outbreaks.
Forest tent caterpillars can defoliate a large number of broadleaf trees and plants. In Minnesota, quaking aspens, Populus tremuloides, are most frequently attacked. Other highly preferred tree species in Minnesota include balsam poplar, basswood, oaks, ashes, birches, alder, and fruit trees. When trees are defoliated, forest tent caterpillars may also damage other nearby plants.
Damage has been found on vegetables, fruit trees and other small fruits, and nursery crops. This caterpillar rarely feeds on red maple and conifers, such as pine and spruce. Trees that are fed upon by forest tent caterpillars are rarely killed by these insects because following complete defoliation, deciduous trees are able to produce another set of leaves during the same season.
The main impact of forest tent caterpillar feeding on deciduous trees is a reduction in the rate of growth. Vigorously growing trees can tolerate up to two or even three consecutive years of heavy defoliation without suffering serious damage or mortality. If a prolonged defoliation cycle occurs, four or more years , moderate to heavily defoliated trees may experience a reduction in growth, suffer branch dieback and could eventually be killed. A general rule of thumb is that complete defoliation can occur when an average of nineteen egg masses are found on an aspen tree that has a six inch diameter trunk at about four and half feet.
When trees become stressed, such as during a drought, they are less tolerant of defoliation. A stressed tree can be injured or even killed in a much shorter time period than an unstressed tree.
Protecting high value trees would be appropriate during forest tent caterpillar outbreaks when trees are under moisture stress. When mature larvae wander to find a place to pupate, their search often takes them to nearby buildings and yards. They do not bite people or harm animals or property, but they can be very annoying when large numbers are found crawling or clustering on building walls, lawns, and sidewalks.
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