You may not know the name, but in the past couple of years, you’ve seen the results of their work. Trees of many varieties, completely stripped of their leaves, leaving a ghost-like appearance resembling a Halloween party decoration. While some have said that the worms do not hurt the tree, it stands to reason that the part of the tree responsible for collecting food to send to roots and fruits can no longer do its job. That has to cause damage—at least a major setback—to the living cycle the tree.Let’s take a look at the caterpillar. These inch-long green or yellow critters, bristling with silky hairs, are actually moth larvae. In summer and early autumn they weave expansive webs that bind together the ends of branches. They eat every leaf within reach, continually building larger webs until late autumn, when they pupate. Resembling dirty rags and filled with black droppings and wriggling worms, the webs ruin the aesthetics of any garden.
Besides aesthetic concerns, web-worms can seriously damage the harvest of fruit and nut trees. Not only can they quickly consume vast quantities of leaves that are needed for fruit production, but they also bind up the ripening fruits and nuts in their webs.
As many folks will attest, they can seem nearly impossible to fight. Their webs are often out of the reach of conventional sprayers; commercial spray equipment can result in a rain of pesticide over large areas of your garden.
In early spring, moths hatch from cocoons carefully hidden in the bark of tree trunks and in ground debris. The adult moths are about 2 inches from wingtip to wingtip and are white spotted with brown. They lay eggs in clusters on the leaves of suitable host plants.
The eggs hatch within a week. Out come tiny caterpillars, the first generation of the growing season, spinning webs and eating leaves. This first infestation is so mild that sometimes the webs go unnoticed.
The first-generation caterpillars have eaten their fill by early summer. They form cocoons and pupate, usually in the bark, of a tree or underneath leaves or other debris on the ground. By midsummer they re-emerge as moths. A second generation follows — this time larger and more destructive.
Because the webworms — in one form or another — are present year-around, it’s possible to devise a year-round strategy for dealing with this pest
In winter or early spring, remove fallen leaves, ground debris and mulch, which may harbor over-wintering webworm pupae. Replace the debris with fresh, pest-free mulch.
Inspect susceptible plants for the greenish egg masses, which are typically laid on the undersides of leaves and are protected by a woolly or scaly covering. Eggs are deposited from late spring through fall. Remove any affected leaves and destroy them. This strategy requires time and sharp eyes and is obviously impractical for tall trees.
Bacillus thuringiensis (Bt) is a microbial pesticide that can be applied as a dust or spray. It kills many types of caterpillars but has no effect on warm-blooded animals or bees.
With fall webworms, Bt is effective only if its application is properly timed. Once the caterpillars have enshrouded themselves in webs, they are more difficult to kill. Check on susceptible plants frequently, beginning in late spring, and apply Bt at the first sign of hatching webworms. Bt loses effectiveness after about two days, so it must be reapplied as long as more larvae are hatching.
Always use Bt with care, because it also can kill the larvae of non-pest moths and butterflies.
When you see webs, clip the infested branches and burn them, or drown the larvae in a bucket of soapy water. A pole pruner with a lopper blade will help you reach webs within 16 feet or so of the ground.
One of the ways we handled the worms in the Willamette Valley was to clip the limb and burn the whole nest. It didn’t stop them from reappearing the following summer, but it slowed their spread to what seemed manageable.
The infestation in Douglas, Josephine and Jackson counties seems beyond the “lop and burn” method. According to farm and garden stores, a preferred treatment should be applied in the spring. Then, the homeowner can apply a systemic, which contains an insecticide and a fungicide. The worms appear in summer and fall, so this type of preventative will have had time to work its way to the roots then up to the leaves of the trees.
Another solution, while chancy, is to open nests and allow birds to pluck the web worms from the nest. Birds can make a feast of the soft-bodied worms. But you do take the risk of the birds not getting all the egg laying worms.
While you can control the infestation on your own property, you can’t control what happens on your neighbor’s or on public lands. Winter is the best solution, where a hard freeze will kill many of the pests.
If you have questions, call one of the many farm and garden stores in your area for expert advice on dealing with the situation.