The foliage at the ends of the branches on my honey locust are turning brown. Why?
The browning of the honey locust foliage is probably due to the mimosa webworm. Damage occurs when the caterpillars tie honey locust leaflets together and feed on the foliage inside the tightly compressed, protective webs. Affected foliage gradually turns brown. There are two generations of caterpillars per year. Extensive damage is most obvious following the second generation in August.
Damage from the mimosa webworm is seldom serious to otherwise healthy, well-established trees. The webs and browned foliage are unsightly. The damage is more aesthetic than serious.
Chemical control for mimosa webworm is rarely warranted. Treatments after the foliage has turned brown are ineffective and a waste of time. Such late treatments may do more harm than good by destroying the natural enemies of the pest rather than the pest itself. Sprays must be applied at the start of the caterpillar period and before webbing is apparent to be effective (mid-June and again in early August in Iowa). Insecticides available to homeowners include Bacillus thuringiensis (Dipel, Thuricide, etc.), Sevin, permethrin, and spinosad. Carefully read and follow directions on the insecticide label.