Tent Caterpillars

By: Jennifer LaMontagne- Assistant Horticulturist- Bloch’s Farm- Green Lake, WI

Summer is the time of year to observe your plants closely for diseases and pests. Have you noticed any tent-like webs or worms crawling on your ornamental, fruit, or woodland trees? Around our area and in many parts of the state, two tent-building caterpillars are Eastern tent caterpillars and webworms.

Eastern tent caterpillars overwinter in egg masses on the twigs of their host plants. Larvae normally hatch at about the same time that the host plant is beginning to leaf out. Their favorite host plants include apple, crabapple, hawthorn, wild cherry, mountain-ash, cotoneaster and many other ornamental trees. Larvae create silken tents in the branch crotches and emerge at night from the tent to feed. Feeding damage can range from barely noticeable to serious defoliation, depending on the number of caterpillars and the size of the tents. As larvae mature, they leave the host plant and look for a place to make their cocoons. The adults then turn into moths and emerge in late June or early July. If you inspect your trees closely, egg masses can be found encircling twigs throughout the winter and early spring. On small trees the egg masses can be removed manually by carefully scraping them off before young larvae hatch.

Webworms are often confused with Eastern tent caterpillars. Webworm nests are seen more in the late summer and fall, whereas the Eastern tent caterpillar nests are usually seen in the late spring or early summer. Webworms build their nests around foliage and on the ends of branches, while the Eastern tent caterpillars usually form their nests in between branches.

Removal of the small tents by pruning is effective early on or spraying the newly hatched worms with a homemade concoction of dish soap and water. Burning the tents and caterpillars with a small torch is also common, but this is a hazardous procedure that can seriously injure the tree if not done carefully. As the tents and caterpillars get larger a pesticide application may be needed, and any type of control works best with repetition. If you destroy the tent but don’t kill every worm they will simply rebuild on a different branch of the tree. 

Bloch’s Farm carries safe and effective products to control tent caterpillars such as Monterey Garden Insect Spray (with Spinosad), Thuricide Concentrate (Bacillus Thuringiensis), and Tree and Shrub Insect Control Systemic Drench. Before spraying use a stick to ‘open’ the tents to ensure that the pesticide gets in. It is very important to read carefully and follow closely all label directions when applying any kind of chemicals.

Bloch’s Farm is open 7 days a week: 8 am to 5 pm Monday – Saturday and 10 am to 4 pm Sunday. Check out our huge selection of trees, shrubs, and perennials too! Stop in today and our knowledgeable staff will be happy to help you. Feel free to call 920-294-6000 or e-mail jlamontagne@blochsfarm.com with any questions. Visit our website online at www.blochsfarm.com and follow us on Facebook and Instagram. Join us for this weekend’s sale! August 13th – August 15th: 20% Off Bagged Goods!

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