by Lis Friemoth

These tents not for camp

You know spring is in full swing when the tent caterpillars are busy making webs. There really isn’t cause for panic or even much concern, unless populations are heavy in a particular plant or area of the landscape. What makes these critters tick? And if they are troublesome, what can you do?

The technical name for this web-spinner is Malacosoma americanum (Fabricius) — or eastern tent worms. They are quite common from the east coast to the Rocky Mountains and up into southern Canada. Eastern tent caterpillars have only one generation per year and are not the same critter we see in the fall.

In spring, the small larvae emerge from their winter home (egg mass) and begin life by sunning themselves on and around the egg casement. Almost immediately, they begin to build a tightly woven, common web that serves as the home base for resting and molting. Movement and feeding schedules are relatively consistent. During the day, or when it’s rainy, they are most often found inside or near the web (the best time to eradicate the entire web and occupants).

In early evening, they move out of the web to feed on surrounding and available foliage. As the foliage is eaten, and their size increases, the web is enlarged to accommodate the physical needs and changes.

When food runs out, you may see them, en masse, migrate to a new food source. And yes — they will crawl across roads, over houses, or whatever they need to traverse, in their search for food. Only in the later life stages will individual larva be seen feeding solo; otherwise, this is a very communal group. They move, eat and rest together. In about three weeks, they mature into tannish-brown-colored moths.

After mating, the female moths will each lay one mass containing anywhere from 150 to 350 eggs around the branches of host plants. The female then exudes a somewhat sticky substance encasing the egg mass, which ages into a hard, shiny covering that will protect the eggs over winter. The egg masses look kind of like a small piece of dark-gray to black foam wrapped around the branch.

In the spring, the eggs hatch and a new crop of larvae emerge. Populations are cyclical and peak once every 10 years or so. At their peak, one or two good-sized webs can defoliate an entire tree. But even so, they are not considered serious pests.

The range of host plants includes all fruit-producing and ornamental apples, ash, birch, black cherry, chokecherry, hawthorn, oak, peach, pear, plums and willow. The overall condition of the plant attacked will determine the amount of fatal damage. Small populations may not be enough to warrant much attention. If plants are under stress from successive years of problems, and infestations are heavy, expect to lose some major branches.

Control is not particularly difficult. If you want to treat for the caterpillars, catching them early is the key to minimal risk control. The easiest method is to physically remove the webs. This can be done by hand picking (use a piece of newspaper or wear a glove if you’re squeamish). The larvae will need to be killed in order to prevent them from just wandering off to find another location to build a web.

Placing the removed critters into a bucket of warm, soapy water should take care of them. If you are one of those that likes to burn things, yes, you can do that, too. Remove the web and contents from the tree and place into a flame-proof container before lighting the fire. Be sure burnins is legal — with or without a permit — where you live.

If you would like the less-aggressive approach, spraying them with insecticidal soap, horticultural oil, or Bt will work during the early periods just after egg hatch. As the larvae age, it is more difficult to eradicate them without physical or chemical intervention. If you choose a chemical route, there are many products labeled for eastern tent caterpillars. Just read all labels before you purchase or use products, since all products you use must be labeled for the plants/problem/critter you are treating.

Just a reminder: Be sure to visit The Mitchell Park Conservatory in Milwaukee, also known as The Domes, while you have a chance. From June 22 through Sept. 19, The Domes will close for facility improvements. Visit now for a sweet smell of summer, and enjoy the Arid Dome featuring cacti and succulents, the Tropical Dome showcasing the diversity of the rainforest and the themed Floral Show Dome. The Domes are open 9 a.m. to 5 p.m. daily at 524 S. Layton Blvd. Call (414) 649-9800.

— Lis Friemoth is a horticulture diagnostician. Contact her at (262) 745-2904, P.O. Box 58, Springfield, WI 53176, visit online at www.thegardenhoe.com or e-mail her at gardenhoe@tds.net. Listen to Liz from 9 a.m. to 10 a.m. every third Saturday on WISN AM1130 radio.

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