Web worms infest fruit trees

NIAGARA, Wis. -The silken-like web masses found on some area trees are a cause for concern, but are not highly damaging, experts says.

“These masses make people think that they have Eastern tent caterpillars munching away on their trees,” said Scott Reuss, University of Wisconsin- Extension horticulture agent in Marinette County. “However, their trees are actually being chewed upon by a long-lost relative of the tent caterpillar called the fall webworm.”

Webworms are found in groups within their web masses, feeding on tree leaves. They feed on most broadleaf tree and shrub species, but are very commonly found on apple and other backyard fruit trees.

Although just as unsightly, webworms are less damaging to trees than are the tent caterpillars. As their name suggests, fall webworms show up fairly late in the growing season, whereas tent caterpillars appear in fairly early spring.

“Although webworm damage is highly visible, it is generally not very detrimental to tree health,” Reuss said. ” The best plan of action is to be proactive and remove the webs (or kill the enclosed caterpillars) before the caterpillars reach the larger stages when they can devour a lot of leaf area every day.”

Small trees are more at-risk than are large trees, but the webworms are also easier to control on small trees.

The best method is literally hand control -squishing them while still on the tree, Reuss said.

“You can also prune out the branches that are infested with the webworms and then crush the insects, but this probably does more damage to the tree than the caterpillars’ feeding damage,” he said.

Physical control is relatively easy on small trees, especially if you look through your trees consistently and catch the critters before their populations build to large numbers. Walking around and looking at your trees once or twice a week for the web masses may allow you to save lots of time and money controlling them later, and will keep your trees healthier, as well.

“In larger trees where crushing is not an effective option, patience and acceptance may be the next best option,” Reuss said. “It may be difficult to watch the insects, but it is unlikely that they will cause enough damage to warrant the cost of insecticide use – in part because it is difficult for homeowners to effectively treat large trees on their own.”

If you are in a situation where insecticidal use is your best option, some common insecticides labeled for use against webworms include: Bacillus thuringiensis (Bt), methoxychlor, or carbaryl, Reuss said.

Make sure to use them properly, wear rubber gloves and protective clothing, and carefully follow all label directions.

“Another chemical option considered safer by many is the use of an insecticidal soap solution,” Reuss noted. “These solutions can work well if applied to young webworms and they are given a thorough soak of the solution. Also, because the webworms are actively feeding outside of their protective web only at night or during lower light conditions, spray applications are best done early in the morning or late in the day.”

If you have questions about how to deal with webworms or any other plant problem, call the Marinette County UW-Extension office at (715) 732-7510 or the Florence County UW-Extension office at (715) 528-4480 or e-mail your questions to Scott Reuss, UWEX Horticulture Agent, at scott.reuss@ces.uwex.edu.

Information is also available by contacting the Dickinson Conservation District at (906) 774-1550.