Fall Webworms – A Nuisance and Pest

If you have a fruit tree, mulberry or ornamental fruit tree, you may be experiencing an infestation of insects called fall webworms.  The first sign of them in a tree is a cottony mass of webbing, inside of which are dozens of 1 inch (plus or minus) sized white to tan fuzzy caterpillars.  The first reaction upon seeing them may be like Henny Penny and “the sky is falling”, but overall, this is more of a nuisance than a serious pest.

 

When infested, in mid to late summer the outer branches of many deciduous trees can become covered with webs.  In some cases, a biological control of sorts occurs, with birds flocking to the tree to feed upon them.  That’s cool.  No need to worry about what do to, just let the birds have their meal.

 

In other situations, the birds are of no help, and property owners must intervene to avoid extensive defoliation.  In fact, control efforts are best if implemented sooner than later, as the webs themselves serve as a protective device to shield the caterpillars from any outside force.

 

Although this late season defoliation is too close to the time of leaf drop to seriously harm plant health, most property owners prefer to keep these unsightly webs off their trees.  Upon seeing them in a tree, the following actions are recommended:

 

*Simple hand removal; just ripping them out of the tree’s canopy.  You might want to wear gloves to avoid contact with the fecal material, and wash your hands afterwards.

*Using a leaf rake to pull the web masses off the branches.

*Using a strong stream of water from the garden hose to dislodge the webs.

*Applying an insecticide to control them.  This method has limitations.  The web masses often serve to buffer or separate the insects from the actual product.  Control efforts made in the early stages of infestation are most effective.  Bacillus thuringiensis, acelepryn, bifenthrin and permethrin are effective when applied directly to the caterpillars. Be sure to read and follow all label directions with these products.

*Hiring an arborist to remove or spray the insect masses.  This is especially important if the tree is large and they cannot be reached from the ground.  Climbing any ladder other than a sturdy step ladder to work in a tree is dangerous and should not be attempted.

John Fech
Horticulture Extension Educator at Nebraska Extension
John Fech is a horticulturist with the University of Nebraska-Lincoln and certified arborist with the International Society of Arboriculture. The author of 2 books and over 200 popular and trade journal articles, he focuses his time on teaching effective landscape maintenance techniques, water conservation, diagnosing turf and ornamental problems and encouraging effective bilingual communication in the green industry. He works extensively with the media to extend the message of landscape sustainability, making over 100 television and radio appearances each year.
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