Fall Webworm – the next closest thing to ugly

Timothy Gibb, Insect Diagnostician, Purdue University

Not to be confused with bagworms, fall webworms are the caterpillars that create the ugly mass of spiderweb-like webbing on the ends of branches of many trees in yards, parks and along roadsides. They are most apparent beginning in mid to late summer and persist on through the fall. The web or mass begins when the tiny newly hatched caterpillars enclose a leaf or two and begin feeding on it. As they grow, the web mass also grows to encompass a whole branch or sometimes two by the end of the season.

If one were to have the courage to look closely into the mass of webbing they wuld probably observe many light yellowish-green, caterpillars with broad, dusky strips down their back and a yellowish stripe down each side. Heads are usually reddish black and the entire caterpillar is covered by long silky gray hairs. Individually, these caterpillars are not remarkable, but seeing a web full of hundreds of these caterpillars munching away on a tree in your yard can be somewhat alarming.

This is one pest that is actually native to North America. It attacks nearly 100 different trees including persimmon, pecan, sweetgum, walnut, maple, elm, hickory and most fruit trees.

Feeding damage by the fall webworm is usually of only minor economic importance in hardwood forests or along roadsides. However, shade trees and ornamentals closer to homes can be heavily defoliated and the presence of the large, unsightly webs can certainly damage them aesthetically. 

In some cases defoliation of a branch can kill individual limbs. Persistent complete defoliation of entire trees may cause death to young or newly transplanted trees, but this is uncommon. 

In most cases the best method of dealing with these frightful messes, is to employ a long handled pruner and simply cut out the offending branch nest and all. Bag, burn or otherwise destroy the nest. Chemical and biological alternatives include the following:

Biologicals
         Bacillus thuringiensis (BT)
         Spinosad (Conserve, Fertilome etc)
Insect Growth Regulators
         Diflubenzuron = Dimilin
         Fenoxycarb  = Precision
         Tebufenozide   = Confirm
         Pyriproxifen  = Distance
         Neem, Azadirachtin
Conventional pesticides
         Bifenthrin  (Talstar,Onyx)
         Cyfluthrin  (Decathalon)
         Deltamethrin  (Deltagard)
         Fluvalinate   (Mavrik) 
         Permethrin (Astro, Spectracide)

Click image to enlarge

Fall webworm. Hyphantria cunea, Order Lepidoptera: Family Arctiidae