Overrun with tentworms

Asked June 19, 2020, 9:22 PM EDT

Our yard is filled with mature oak trees, pine trees and a few other ornamental trees/shrubs. Over the past 10 days, there has been progressive damage noted by tentworms, especially on the oak trees initially, now also leading to loss of needles on the pine trees. There are a few worms on the exterior of the house, but primarily limited to extensive presence on the trees. In fact, you can hear them eating and their excrement is visible on the sidewalk. On Tuesday (6/16) I sprayed SEVIN around the trees, the home foundation and as far up the trunks as possible. On Thursday, TruGreen treated all trees and shrubs with cyfluthrin/propiconazole/imidacloprid. The technician thought the spray would blunt the infestation, but not eliminate the infestation. It was further suggested that we contact the extension service to identify a more "industrial approach" that would reach the top of the trees (approximately 50') and be more effective. We live in a heavily wooded subdivision of about 25 homes and the infestation seems to be spreading. Looking for your recommendation.

Mecosta County Michigan

1 Response

Hello,

Those are most likely gypsy moth caterpillars, Lymantria dispar (Lepidoptera: Lymantridae).

The Wisconsin Department of Natural Resources has an excellent web site on Gypsy Moth at http://www.gypsymoth.wi.gov/

From this site you can download and print their new comprehensive Gypsy Moth & Management booklet at http://dnr.wi.gov/forestry/feeds/pdf/FR-405-2008.pdf

The following was taken from the USDA – Forest Service fact sheet entitled Forest Insect & Disease Leaflet 162 (at http://www.na.fs.fed.us/spfo/pubs/fidls/gypsymoth/gypsy.htm)

The gypsy moth is not a native insect. It was introduced into the United States in 1869 by a French scientist living in Massachusetts. The first outbreak occurred in 1889. By 1987, the gypsy moth had established itself throughout the Northeast. The insect has spread south into Virginia and West Virginia, and west into Michigan. Infestations have also occurred in Utah, Oregon, Washington, California, and many other States outside the Northeast.

Life Cycle

The gypsy moth passes through four stages: egg, larva, pupa, and adult (moth stage). Only the larvae damage trees and shrubs.

Gypsy moth egg masses are laid on branches and trunks of trees, but egg masses may be found in any sheltered location. Egg masses are buff colored when first laid but may bleach out over the winter months when exposed to direct sunlight and weathering.

The hatching of gypsy moth eggs coincides with budding of most hardwood trees. Larvae emerge from egg masses from early spring through mid-May.

Larvae are dispersed in two ways. Natural dispersal occurs when newly hatched larvae hanging from host trees on silken threads are carried by the wind for a distance of about 1 mile. Larvae can be carried for longer distances. Artificial dispersal occurs when people transport gypsy moth eggs thousands of miles from infested areas on cars and recreational vehicles, firewood, household goods, and other personal possessions.

Larvae develop into adults by going through a series of progressive molts through which they increase in size. Instars are the stages between each molt. Male larvae normally go through five instars (females, through six) before entering the pupal stage. Older larvae have five pairs of raised blue spots and six pairs of raised brick-red spots along their backs.

During the first three instars, larvae remain in the top branches or crowns of host trees. The first stage or instar chews small holes in the leaves. The second and third instars feed from the outer edge of the leaf toward the center.

When population numbers are sparse, the movement of the larvae up and down the tree coincides with light intensity. Larvae in the fourth instar feed in the top branches or crown at night. When the sun comes up, larvae crawl down the trunk of the tree to rest during daylight hours. Larvae hide under flaps of bark, in crevices, or under branches - any place that provides protection. When larvae hide underneath leaf litter, mice, shrews, and Calosoma beetles can prey on them. At dusk, when the sun sets, larvae climb back up to the top branches of the host tree to feed.

When population numbers are dense, larvae feed continuously day and night until the foliage of the host tree is stripped. Then they crawl in search of new sources of food.

The larvae reach maturity between mid-June and early July. They enter the pupal stage. This is the stage during which larvae change into adults or moths. Pupation lasts from 7 to 14 days. When population numbers are sparse, pupation can take place under flaps of bark, in crevices, under branches, on the ground, and in other places where larvae rested. During periods when population numbers are dense, pupation is not restricted to locations where larvae rested. Pupation will take place in sheltered and non-sheltered locations, even exposed on the trunks of trees or on foliage of nonhost trees.

The male gypsy moth emerges first, flying in rapid zigzag patterns searching for females. When heavy, egg-laden females emerge, they emit a chemical substance called a pheromone that attracts the males. The female lays her eggs in July and August close to the spot where she pupated. Then, both adult gypsy moths die.

Four to six weeks later, embryos develop into larvae. The larvae remain in the eggs during the winter. The eggs hatch the following spring.

Hosts

Gypsy moth larvae prefer hardwoods, but may feed on several hundred different species of trees and shrubs. In the East the gypsy moth prefers oaks, apple, sweetgum, speckled alder, basswood, gray and white birch, poplar, willow, and hawthorn, although other species, like blue spruce for example, are also affected. The list of hosts will undoubtedly expand as the insect spreads south and west.

Tactics Directed Against the Gypsy Moth

  • Remove objects around the outside of the home that provide shelter for gypsy moth larvae and pupae, such as flaps of bark, dead tree branches, dead trees, boxes, cans, or old tires.
  • Diversify the composition of trees and plants on your property to include species not preferred by the gypsy moth, such as tulip or yellow poplar, honeylocust, ash, hickory, dogwood, mountain ash, and many conifers.
  • Destroy egg masses found on outbuildings, on fencing, and in woodpiles. Simply scraping egg masses onto the ground will not destroy them. Burn them or soak them in kerosene or soapy water. Caution is urged because the hairs that coat the egg masses can cause allergic reactions. Egg masses can also be destroyed by planting them with commercially available products, such as liquid detergents.
  • Place burlap on trees, especially oaks, to provide shade and shelter for older larvae when they seek out protected resting places during the day. The number of larvae and pupae that rest under the burlap provides valuable information about the severity of infestation on your property. When populations are sparse, larvae and pupae beneath burlap can be manually destroyed.
  • Use barrier bands, consisting of commercially available double-sided sticky tapes, or sticky material such as Tanglefoot, petroleum jelly, or grease, to prevent larvae from crawling up the trunks of susceptible trees. These products should be applied to the surface of an impermeable material, such as duct tape or tar paper, and not applied directly to the bark. Petroleum-based products can cause injury (swelling and cankering) on thin-barked trees.

Maintaining and Enhancing the Health of Trees

  • Enhance growth conditions for isolated trees by encircling them with mulch or ground cover plants that do not compete for moisture and nutrients the way dense grass layers do.
  • Water shade and ornamental trees in periods. of drought to maximize recovery during refoliation.
  • Fertilize shade trees.
  • Avoid stressing trees. For example, construction projects tend to compact soil and prevent moisture from penetrating to small feeder roots.
  • Avoid applying lime or weed killers around trees. These chemicals can seriously damage shallow tree roots.
  • Thin woodlot trees and groups of shade trees between outbreaks to reduce competition.

The Use of Pesticides Against the Gypsy Moth

The decision to use pesticides is influenced by a number of factors:

  • The number of visible egg masses.
  • The percentage of preferred hosts in a mixed stand of trees (50 percent or more of oak).
  • Whether trees already have dead or dying branches, especially near the top branches or crown.
  • Whether the property is located adjacent to wooded areas heavily infested with gypsy moths.

During periods when numbers of gypsy moth larvae are dense, pesticides may be the most effective method of reducing the number of larvae and protecting the foliage of host trees. Application of pesticides should be done by a certified applicator, because special equipment is required. Large acreages, such as wooded residential areas and forests, should be treated by aircraft.

For homeowners, the best products for controlling gypsy moth caterpillars on ornamentals are cyfluthrin (sold as Bayer Advanced Vegetable and Garden Spray), bifenthrin (sold as Ortho Bug B Gon) and carbaryl (sold as Sevin). Be sure to read and follow all instructions on the label before using any pesticide.