CUISINE & CULTURE
There is a reason the insect Hyphantria cunea has the common name ‘fall webworm.’ Its large silky webs are woven in the fall. Webs look menacing, but infested trees usually recover with little long-term damage.
Worms are the larval stage of small white moths. The life cycle of the fall webworm begins with the female laying hundreds of eggs on the undersides of leaves in early summer. The eggs develop in a week or two into greenishyellowish larvae. They are easily distinguished by the parallel rows of black dots running down their backs.
The larvae form a community as they feed together, staying grouped. They construct the silken webs as they begin feeding. Webs start small, encompassing single leaves, but as larvae mature their webs become larger, enveloping a greater number of leaves and eventually entire branches. Inside the web larvae make a microclimate where temperatures can be regulated, typically above 122 °F.
The worms can quickly defoliate a tree, leaving only veins of the leaves as they feed. This is when larva get busy as they morph into pupae, taking about 8 weeks to fully develop. When fully mature the larvae spin thin cocoons and pupate in leaf debris and bark crevices.
Infestation is usually confined to one tree but webs in severe infestations can cover an entire individual tree and surrounding trees.
Fall webworms are known to feed on over 300 hardwood species. In our region the most common are sumacs, pecans, walnuts, and persimmons. Adult females choose trees with succulent new growth on which to lay their eggs.
The most effective control is to diligently inspect susceptible trees. Once an infestation is found, remove affected limbs by pruning the entire area covered by the web. Often webs are constructed high in the canopy, leaving the best remedy to knock down or tear open the web. A torn web exposes the larvae, which allows natural predators like birds and beneficial insects to attack the larvae.
Chemical sprays are ineffective on the webs but can be effective at the egg stage when larvae are hatching. The biological pesticide Bacillus thuringiensis (Bt) can be an effective control. Other chemical applications are effective but always follow label directions and target foliage surrounding the web with the spray.
Several generations can occur in a year. Stay vigilant.
Some information from clemson.edu
Ellen Peffley Harp, a retired professor of horticulture at Texas Tech University, writes about gardening for several Texas newspapers.
