Landscape - Fall Webworms

It is the time of the year to see fall webworms on many trees and shrubs. The following is more information.

Fall webworms feed on over 85 species of trees including, walnut, hickory, fruit trees, maples, cherry, and sweetgum. There are two generations in the mid-Atlantic area. Fall webworm overwinter as pupa in leaf litter, old nests, or in crevices found in bark, and emerge sometime in mid to late June. Females lay eggs on the underside of leaves and egg hatch occurs between 802 and 1517 [1105 peak hatch] GDD. The larvae are pale yellow to pale green with black spots along the back. Caterpillars are covered with long white to yellowish colored hairs. The second generation of fall webworm is seen later in the summer with peak egg hatch at 2723 GDD. Physically remove the nests and tear open nests with pruners, or a stream of water from a high pressure hose. Natural enemies such as birds, predatory insects and parasitoids will take advantage of damaged nests. Chemical control if necessary may include B.t., insecticidal soap, spinosad, tebufenozide, diflubenzuron, or a pyrethroid.

Fall Webworm. Photo from the Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Bugwood.org

Information from Brian Kunkel, Ornamental IPM Specialist, UD

Landscape - Current Pests

The following are some pests currently active in DE landscapes that you should watch for.

First generation fall webworm is being found on apple, crabapple and persimmon. Don't think it's the old tent caterpillar tents! Mechanical disruption of the web now will lessen the second generation.

The “Shothole” damage from Tortoise beetle feeding is prevalent on annuals (Ipomea ,etc.) and some perennials.

Rose midge is active this year again in many locations. Look for the “blighted” shoot tips on the terminal growth only.

Powdery mildew is all over crepe myrtle, lilacs, and other shrubs and flowering trees due to warm moist conditions combined with succulent new growth. Fungicides and sanitation may be required to prevent spread or overwintering.

Cicada Killer wasps are solitary wasps and are very unlikely to sting. Males fly at people, dogs, cats, other insects, etc. but are unable to sting. Females prefer to dig holes and sting cicadas. Treatments are rarely warranted.

Information from the current edition of the Ornamentals Hotline Newsletter from the University of Delaware Cooperative Extension.

Landscape - More on Fall Webworm

The following is more information on fall webworm, a common pest that is seen in late summer.

This year is another “epic” performance by Fall Webworm (Hyphantria cunea) for best defoliation and webbing by a caterpillar. The characteristic “ghostly webs” are on branch terminals everywhere hickory, pecan, black cherry, but especially mulberry and mountain ash. Over 88 tree species have been noted in the USA as being susceptible. There are two generations per year. The white adults emerged and laid eggs earlier this year after overwintering as a cocoon in soil or debris. It usually takes approximately 6 weeks for full larval development, and the maturity of the second generation is definitely upon us. The larvae are yellow with white hairs when young. Once more mature, their hairs will be longer and come from orange or black spots so larval appearance will vary. These caterpillars have either a black or red head. There are actually two “races” of this pest in our region thus the difference in larval appearance. The caterpillars usually feed together in the same tent, but wander once older. Scouting for and pruning out small webs is a good option. At this point, it may be best to prune out this year's infestations and avoid spraying for it entirely. Damage from fall webworm is cyclical and reaches its peak once every four years or so. Several birds, wasps, yellowjackets, and other parasites will feed on them. Spraying through the large webs has limited effectiveness even with broad spectrum contact pesticides and coverage will be an issue. B.t. is not a good option against mature caterpillars and has had limited effectiveness against fall webworm for us. Plus, you'll still have the webs to deal with anyway. The damage is
mainly aesthetic.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens

Landscape - Fall Webworms are Out

You can see many trees with webs on the tips of branches now across Delaware. The following is some information on fall webworm.

Silky tents made by fall webworm caterpillars are beginning to appear now on the branch tips of walnut, hickory, ash, elm, crabapples and other types of trees. The small yellowish-gray webworm caterpillars hide in the webs during the day. Some trees have actually been defoliated from having a tent on nearly every branch. But in most cases, each tree has three or four tents. They look bad, but cause little harm. Tree health is not affected until more than 50 percent of the foliage is consumed, and even then, the trees usually come back just fine the following spring. Pruning-out infested branches is the best strategy if you can reach them. Spraying the foliage around tents with B.t., Sevin, Orthene, or a pyrethroid insecticide will prevent further feeding injury, but the old tent will remain visible for several months. We have many natural parasites and pathogens of fall webworm that will eventually bring infestations under control. Outbreaks usually last two or three years.

Fall webworm on cherry. Photo from Penn State University.


From the July 25 2008 edition of the Michigan State University Landscape Alert Newsletter.