June 11, 2021
good to grow
KENTON COUNTY EXTENSION eNEWSLETTER
Dan Allen - Extension Agent for Agriculture and Natural Resource Education
Oh, What a Web We Weave: Fall Webworms & Tent Caterpillars

There are a couple types of caterpillars that enclose themselves in webbing that you have undoubtedly seen in past years. These are the tent caterpillars and webworms. Tent caterpillar eggs are laid on stems and the young caterpillars enclose the area in webbing. The eggs usually hatch mid to late March. There is one generation per year. These ‘tents’ are found in a fork of branches. They leave the tent/nest to feed on emerging leaves and return after feeding. In contrast, the fall webworm has a spring and a fall generation. The fall webworm adult lays eggs on the underside of a leaf later in the spring and the larva emerge to create the webbing, which is found at the ends of branches, enclosing a meal of leaves. The webbing ‘grows’ as the caterpillars grow and need more food. Be on the lookout for the webbing. Remove the twigs with the webbing or pull the webbing off the tree if it can be reached safely. This is best done early in the day or at dusk while the caterpillars are still in the nest. Dispose of the inhabited nest by submerging it in a bucket of soapy water or crushing it. Do not try to burn it when it is on the tree which can cause more damage to the tree than the insect itself. The damage done by the feeding of these insects is largely aesthetic although very large infestations on smaller trees can weaken the tree. Eastern tent caterpillars can be especially dangerous for pregnant mares if ingested. Since these are true caterpillars, Bt can be used when they are young and actively feeding but a hole should be made in the webbing to get the material onto the leaves. While Bt can target the caterpillars, insecticides that target many insects can do damage to the natural predators of tent caterpillars and fall webworms. Using the least damaging strategy of removing the nests can save time and money. Minimizing the numbers of the early generation of fall webworm in late spring and early summer can reduce their numbers later in their fall generation. Contact your local county extension if you have questions about these insects and their management.






Trouble is in the Bag: Bagworms

If you were plagued with bagworms on your landscape plants last year, now is the time to look for this year’s generation. The young are hatching and looking for food. They seem to prefer evergreen trees and shrubs but will also feed on deciduous trees as well. Not only do they feed on plants but they use the plant material to build their protective capsule. The young are very small but as they grow, if numbers are high, they can do lots of damage to plants. As they end their feeding, they attach their ‘bag’ to a branch and overwinter. Keep on the lookout for these critters now, especially if you or a neighbor had an infestation last year. As they emerge, they may ‘balloon’ on a strand of silk to nearby plants. The best time to treat is when they are young and actively feeding. Since they are a true caterpillar, the insecticide Bt would be a good product to target them, leaving beneficial insects unharmed. See the attached publications below, follow chemical control measures recommended for your state. Be sure to read the label for safe use on the plant and precautions to take for yourself when applying any chemical. If you miss this window for treatment, pick or cut the bags off your plants later in the summer to minimize numbers for next year.






Box Tree Moth- A Potential New Problem for Boxwoods
By Jonathan L. Larson, Entomology Extension Specialist

Boxwoods usually have to contend with insect issues like boxwood leafminer or boxwood psyllid. In recent years, we have had concerns arise over boxwood blight, also impacting Kentucky boxwood plants. Now, it seems like a new invasive is on the horizon that could attack these commonly planted shrubs— box tree moth.

What is the box tree moth?

Box tree moth is an invasive species originally from Asia (specifically China, Japan, Korea, and Eastern Russia) and it has been highly problematic for over 25 European nations since first appearing in Germany in the mid-2000s.
Previously, the only North American infestation was located in Ontario, Canada. However, that changed at the end of May 2021 when reports were released that this pest had been discovered in Michigan, Connecticut, and South Carolina. The USDA is taking immediate action to try and contain the issue and stop this from happening again, but we need to be vigilant to make sure we help contribute to monitoring programs.
In its final instar, the box tree moth caterpillar is about a half inch long. They are primarily yellow green in color, with black and white stripes that run vertically down the body on each side (Figure 1). On each abdominal segment there is a pair of black dots.
The adult moth is broadly fan shaped. For the majority of adults, the exterior margins of their wings are brown and there is an inner white triangle that spans the wings and body. Some adults may be completely brown. The box tree moth superficially resembles the melonworm moth in coloration and the patterns on their wings. The box tree moth has white comma-like markings near the wing margins that the melonworm lacks.
Thus far, box tree moth has only been observed to feed on boxwood plants in the genus Buxus. Currently, there are no known resistant varieties of boxwood.

What does it do?

Box tree moth larvae feed on the leaves and the bark of boxwood plants. The younger larvae feed on the undersides of leaves, creating a papery or peeling appearance. As they mature, larvae will eat entire leaves, leaving behind only the midrib. As the plant is defoliated, the larvae will move to feed on the bark, inducing girdling and possibly killing the plant. Older caterpillars also produce noticeable webbed enclosures. These are messy and may contain the caterpillar, its frass, and old cast off “skins.”

How is it different from other boxwood insect pests?

Boxwoods are also hosts to boxwood leafminers and boxwood psyllids that may leave behind damage. Box tree moth is the only caterpillar pest of boxwoods, and their damage is different in comparison to our other pests. Boxwood leafminers cause the leaves to appear blistered as they feed from the inside. There is also an orange or bronzed color caused by their damage, which is focused in the newest growth. Similarly, boxwood psyllid prefers to attack the newest foliage, but they cause the leaves to cup inward on themselves.


What to do if you believe you have found this pest

If you fear you have spotted damage from this pest or have captured a specimen, please contact us at the Department of Entomology or reach out to the Office of the State Entomologist to begin the process of confirmation. We are hopeful we can keep this invader from the state and we appreciate receiving tips from the field.
Figure 1. The mature larva of a box tree moth is about ½ inch long, with yellow-green coloration, black and white stripes down their sides, and a pair of black dots on each abdominal segment. (Photo: Ferenc Lakatos, University of Sopron, Bugwood.org).
Figure 2. Box tree moth is not the only pest of boxwoods, though their damage looks different than the symptoms left behind by boxwood leafminer and boxwood psyllid. Leafminers create blistered, bronze, leaves in the newer growth while psyllids cause the newest growth to become cupped. (Photos: Ferenc Lakatos, University of Sopron Bruce Watt, University of Maine, and Penn State Department of Plant Pathology & Environmental Microbiology Archives, Bugwood.org in order)
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