Identification and Control of Web Worms

webworms and webworm nests


The webworm or fall webworm is actually a caterpillar, and are the larvae of small moths that complete several generations per year.

There are two primary varieties , the blackheaded and redheaded webworm, have light green coloration with numerous black spots. They are covered with long white to faint yellow hairs, have light green coloration and numerous black spots. They are common throughout North America. Webworms are generally discovered when their silken webs appear on trees late in the season . They encase foliage and smaller branches in their silken nests. They differ from tent caterpillars which make smaller nest in tree crotches.

Fall webworm larvae feed on multiple species of trees including fruit trees, nut trees and ornamentals. They devour leaves later in the season and are not as much of a problem in relation to crop loss, the nests however detract from any aesthetic appeal of the landscape and multiple generations over long summers does lead to significant defoliation.

They spin silken webs over plant terminals, then feed on leaves, buds, and blossoms within the webs. The caterpillars will remain within the webbing until food is depleted, at which time new webbing is generated to encase larger areas.

They overwinter in the pupal stage which can be found in the remains of old nests, under loose tree bark and leaf litter. The adults emerge from late Spring early Summer. The eggs are usually deposited in layers of 200 or more eggs on the undersides of leaves. The eggs hatch in 5 - 7 days and a small mass of caterpillars will encase single leaves with their webs skeletonizing the host foliage.

As they grow and food is depleted, they expand and web over additional foliage. The larvae mature in about six weeks, at which time they drop to the ground to pupate. The moths emerge over an extended period in multiple generations, in warmer areas up to four generations can be completed annually.

Other than being unsightly, webworm damage is generally insignificant in most regions. In warmer areas where several generations occur , they can severely defoliate trees. Webworms are known to undergo periodic population spikes every four to seven years which can have a duration of up to three years at which time Mother Natures natural controls will reduce their numbers.

Handpicking is not feasible but Small nests can be pruned out of most trees, or can be easily crushed.

Diverse gardens that include a symbiotic mingling of flowers and vegetables will attract many natural predators. Encourage natural predators such as predatory wasps by mingling varying plants and flowers blooming at different intervals throughout the season. Wasps such as yellow jackets and paper wasps, birds, predatory stink bugs and predatory wasps are known to prey on webworms.

Apply Bt bacillus thuringiensisBacillus thuringiensis for webworm control if they are a persistent problem , it is a bacterium that is known to be highly effective against fall webworms , and is readily available to home gardeners. It's harmless to people and pets. Apply it at either bloom or petal fall, or both. Bt It is a stomach poison and must be ingested . It is more effective when applied during warm, dry weather while the larvae are actively feeding. Bt breaks down quickly in nature so multiple treatments per season is necessary smaller plantings or home gardeners. Broad-spectrum insecticides, such as Pyrethin or malathion only as a last resort.

Sprays/Pesticides must be applied in the pre-bloom stage to prevent injury. Pesticides such as pyrethroids that are more effective in cool than warm weather will work more efficiently against Fruitworms earlier in the season, and is the recommended early season chemical treatment for most Fruitworms.

Proper sanitary practices are vital to the health of your garden. Proper sanitation can help to ensure disease-free pest-free and productive gardens. Try to keep the garden free of any diseased dead or damaged plant materials. Remove cuttings from pruning and trimming and either destroy them - if diseased, or send them to the compost pile. Leaving rotting fruits and vegetables in the garden is like a written invitation to unwanted pests and diseases.

If a diseased or dead plant part has to be cut, the microorganism that caused the problem is probably on the tool you just used. Like a surgeon, sterilize all tools by washing in soap and water - rubbing alcohol wouldn't hurt either. If you pinch off diseased plant parts, wash hands before handling any other plants. Keep Weeds under control. Till the soil in the spring before planting to expose and kill larvae that wintered over in the soil.

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