By Steve Borel
Something is haunting local landscapes these days. Those ghostly webs you’re seeing in pecans and other hardwood trees are the nests of fall webworm caterpillars. Despite their common name, these caterpillars can be seen in Louisiana as early as May and extending into the fall. However, they are not normally this abundant! Yes, their nests are unsightly, but homeowners have nothing to fear. Defoliation by fall webworms at this time of year will not kill affected trees since the leaves have already produced enough sugar for the tree to go dormant and survive into another season.
Adults of the overwintering generation emerge during May or occasionally in late April. Females begin to lay eggs in late May and early June. Each female can lay 400 to 500 eggs in masses on the underside of leaves. Fall webworm larvae pass through as many as eleven stages of development (called instars). They produce a silky web that serves as shelter for the developing caterpillars.
Damage is caused by larvae feeding on the leaves. Fall webworm populations are rarely large enough to defoliate trees except for young trees.
Fall webworm populations are rarely large enough to defoliate trees except for young pecans
Larvae and their webs may be simply pruned out and destroyed, but those infesting the higher canopy will need to be treated to achieve control. When using conventional insecticides that rely on contact, sufficient spray pressure is needed to reach and penetrate the webs of these caterpillars. Several insecticides will normally provide control if adequate spray penetrates the webbing. Reduced-risk products, including those containing Bacillus thuringiensis subsp. spinosad, and insect growth regulators (IGR’s), are applied to foliage near thewebbing and often must be consumed to be effective. Small, young caterpillars are more susceptible to reduced-risk insecticides, so timing of application is important.