Fall Webworms

Kenneth Sharpe, Arledge, Patricia M.  |  11/13/2015 10:08:07 PM

News Article for October 5, 2015:



You may have noticed your trees with webs up in the leaf canopy lately. We are experiencing an unusually heavy infestation of fall webworms.

I see fall webworms almost every year and it seems that most often they are in pecan trees. This year webworm damage is much more wide spread. On a recent weekend trip to north Mississippi I saw lots of webworms along the interstate and out in the rural landscape in a number of different hardwood trees the entire trip.

It appears that sweet gums are a favorite this year but I have seen them in a wide array of trees and some shrubs. I have seen them in pear, persimmon, mulberry, sweet gum, oaks, maple and cypress plus I have them in a dwarf yaupon shrub. They are reported to infest over 600 different species of trees and shrubs.

We can have several generations of webworms this far south but usually we see them in late summer to fall. The moths will lay eggs in mass on the underside of leaves. In about a week those eggs will hatch out a crop of caterpillars. The caterpillars are usually at the tip of branches and will spin an irregular shaped web that will cover leaves, twigs and small branches. On a recent mulberry tree that I saw the different silk webs had grown together and pretty much engulfed the entire tree.

Fall webworms are 1 to 1¼ inches long when mature. They usually have an orange head with pale yellow and/or green body which is covered in long silky hairs that are attached to small humps. The moths are white with a two inch wingspan. Wings may have small brown or black spots or the forewings.

Fall webworms will defoliate trees or parts of trees but usually cause no harm to otherwise healthy trees. It is neither practical nor necessary to treat large healthy trees. Dry weather is already causing some deciduous trees to drop leaves so I would not expect any foliage that the caterpillars eat now to cause any big problems. In the case of small trees or shrubs, you can treat with an insecticide when the infestation first starts if you want to preserve the foliage. The liquid formulation of Sevin or carbaryl would be an effective treatment as well as biological controls of Bacillus thuringiensis such as Dipel or Thuricide. It will be important to either add liquid soap to help penetrate the webbing or tear the webbing with a long cane pole or stick before applying any insecticide so you can get the insecticide inside the webbing. The webbing is spun to protect the caterpillars from predators and is effective at keeping insecticides out also.

I have had several people ask if fall webworms are the same as fall armyworms that sometimes eat ryegrass. They are not; fall armyworms and fall webworms are two different insects.

For more information on these or related topics contact Kenny at 225-686-3020 or visit our website at www.lsuagcenter.com/livingston.

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