Each year in the fall you may notice tent-like webs in hardwood trees with dead or stripped foliage inside. These unsightly webs and foliage damage are caused by a common forest insect in our area, the fall web worm. These are the caterpillar phase of a native moth which tend to cause varying degrees of damage to tree foliage each year. Luckily, the caterpillars’ defoliation is usually late in summer to fall when the leaves are beginning to go dormant in hardwoods. Since the trees have stored most of the energy they need for the winter dormant period the defoliation fall web worms cause is usually not a problem especially on mature trees. Nonetheless the webs are often unsightly and in severe outbreak years they may completely defoliate some trees, particularly smaller and newly established trees. They can be controlled to some degree and luckily bad outbreaks are few and far between. Mostly fall web worms become a problem in home landscapes, orchards, and urban settings. In forests they tend not to cause significant damage but are noticeable due to the tentlike webs. In recent tree plantings for wildlife, they can be problematic by stripping the foliage on the trees.
Here in the Panhandle there can be several generation in a year, and as the growing season goes on the population grows. Earlier in the year the webs are smaller and the caterpillars feeding is less noticeable. By fall when the populations get large, the tentlike nests and stripped foliage is very noticeable. The caterpillars are gregarious and aggregate together close to where they hatch. The female moth lays eggs in the late spring in clutches on the underside of leaves. When the eggs hatch the caterpillars group together and start spinning webs out of silk as the young caterpillars skeletonize leaves. As they grow the web nest becomes larger and more foliage is consumed, forming the large unsightly tent nests we notice in the fall. They tend to form the web tent out toward branch tips and several colonies may form on a tree. The caterpillars only feed on foliage inside the web tent and expand they need more fresh foliage to feed on. The web is a natural defense against predators and by forming the tent nest they can feed in relative safety. As temperature cool and fall comes to a close the caterpillars leave the nest to pupate in leaf litter and bark crevices. They overwinter as pupa to become adult moths next spring. The wind and rain over winter usually removes the web nest and the tree puts on new growth next spring with no lasting damage.
Fall Webworms defoliating a persimmon tree
Photo Credit: UF IFAS Entomology Department
Mostly webworms and their feeding activity are unsightly, especially in landscape settings. The main issue with fall web worm is when a large number of colonies form on a young tree, which can completely defoliate a tree. Orchards are another setting where large outbreaks of webworms can be an issue. When only a couple of web nests form on a tree control is usually not necessary except from an appearance and aesthetic point of view. Fall web worms have a broad range of host plants and will readily feed on a majority of deciduous hardwood trees and shrubs. They seem to favor pecans, hickories, walnut, and persimmon particularly along with sweetgum, yellow poplar, maples, and oaks to a lesser extent. Fall web worm is a particularly troublesome pest in pecan orchards and home landscape pecans. It is important to watch the extent of webworm infestation in these settings, particularly on younger trees. By the time late fall rolls around though removal of the webs and dead foliage may be helpful, but most trees have gone dormant for the year. On young trees that have had total defoliation this can weaken them during winter dormancy, so some TLC and extra attention in the spring are usually good follow ups.
Luckily since fall web worm is a native species there are plenty of predators, parasitoids, and disease that keep these pesky caterpillars in check. If you have a few fall web worm nests in your landscape there are some simple and effective control methods that can be used. One of the best is to simply destroy the web nests and expose the caterpillars to predators. The webs protect the caterpillars from birds and other predators and are their main defense. By simply taking a pole, tool handle, or other implement to reach the web you can simply tear it open and shake it, predators will help do the rest. Another option is to simply prune out the webbed branch, especially since they tend to be towards the tip. They can then be disposed of and the caterpillars along with them. Using sprays and pesticides are usually not extremely effective. Since the caterpillars are inside the dense web any spray usually cannot penetrate the protective web. Treatment of the foliage around the webs can be effective if applied earlier in the year since active feeding will ensure contact with control treatments. Several insecticidal soaps, horticultural oils, and effective insecticides are available and labeled for fall web worm control. This is only necessary in a severe outbreak and timing is everything. If you wait until mid to late fall most feeding activity has ceased and caterpillars will be beginning to pupate for winter, making pesticides ineffective.
Fall web worm caterpillar in the early stages of development. Photo Credit: UF-IFAS Entomology Department
If you are seeing a bit of fall web worm in your area it likely catches your attention. If you have just a few branch tips affected the issue will likely go away on its own. Unless a tree is being almost completely defoliated this pest is more annoyance than anything, despite the unsightly and noticeable webs. If you are just now noticing an issue it is probably best to just wait and let the annual cycle play out. Fall webworm is an unsightly and annoying annual occurrence in trees but luckily it causes minimal damage and can be easily controlled. It is part of our natural landscapes and forests although it can be unsightly and concerning in years with significant outbreaks. For young or recently planted trees it only becomes an issue if complete defoliation occurs and usually the tree will shake this off and leaf out full next spring. Fall web worm can be noticeable and unsightly, but there is really no cause for concern in most cases. As with most things letting nature take its course and the annual cycle play out is usually the best option.
- Fall Web Worms, An Annual Nuisance - November 22, 2024
- The Naval Live Oak Reservation: America’s First Forest Preserve - August 30, 2024
- Thinning-One of The Most Important Forest Management Practices - May 10, 2024