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Dirt Doctor Organic News # 18       Webworms Try to Take Over 

One of the most common pest problems we have in the south this spring is webworms in trees and other plants.  These voracious vegetarians are out of sync time wise, eating a larger variety of plants than normal and much heavier in population than we have ever seen.

Here are the solutions from DirtDoctor.com with appropriate updates for the changes we are seeing.  The culprits in all this are last summer’s drought and this spring’s long, wet and cool weather.

Webworms and all other larvae of moths and butterflies can be controlled, if they need to be, with safe organic techniques.  Webworms, tent caterpillars, loopers, green worms, sod webworms, army worms, leaf rollers and other caterpillars can be killed effectively with a spray of orange oil drench mix, spinosad products or any of the Bt (Bacillus thuringiensis) products.  For the best control, add 1-2 ounces of molasses per gallon of spray.  Even better is to prevent them from becoming a problem in the first place by releasing trichogramma wasps at leaf emergence.  The first step is to tear the webs with a pole so the native wasps can eat them.

For more on this subject see this Friday's House and Garden Section of the Dallas Morning News. 

Webworms on elderberry

       


Webworms on mulberry

                                    

Common names: Fall Webworm, Webworm

Scientific name: Order Lepidoptera, family Arctiidae, Hyphantria cunea (Fall webworm)

Size: Adult--1/2" to 1", larva--1" to 1 1/8"

Identification: These caterpillars are pale yellow, green or beige, black-spotted, and covered with hairs.  Adults are pure satiny white to dusty brown moths.  The larvae form loose, dirty white webs on terminal tree growth from spring through fall.  They eat the foliage within the web.

Biology and life cycle: Pupae overwinter in cocoons in the soil or tree bark.  Adults emerge in early summer to lay eggs in large masses on the undersides of leaves.  Eggs hatch after a few days and larvae feed as a group for about four to six weeks in mid-summer.  White or pale yellow cocoons form in July usually.  There can be several generations a year.  Larvae are light green guzzy worms.

Habitat: Pecan, ash, willow, persimmon, hickory, apple, walnut, mulberry and other deciduous trees.

Feeding habits: Larvae eat outer foliage of trees, especially pecans.  They eat fast and furious and create an ugly mess in the foliage of trees.

Economic importance: The damage to trees ranges from unsightly entangled webs and partial defoliation to complete defoliation which can badly stress trees.

Natural control: Protect the wasps, the birds and the assassin bugs because they eat webworms.  Tear webs with a fishing pole or pole pruning saw to allow the native wasps to control the pest.  Release trichogramma wasps as new foliage emerges in the spring or later if weather is allowing additional hatchings.

Organic control: Spray Bacillus thuringiensis or plant oil products, always at dusk, as a last resort – just on the plants under attack.  Use one tablespoon of molasses per gallon of spray.  Catch larvae in sticky tree bands.  Put tree tanglefoot on masking tape.  Applying it directly to the trunk can insure the tree.  Active worms can also be killed with any of the citrus-based sprays such as the fire ant drench formula.  Spinosad products can also be helpful.

Insight: We have noticed an increase in this pest in direct relationship to the popularity of chemical lawn care companies and the use of aerosol wasp-killer sprays.  Killing the beneficials has given the webworms a free rein.


Naturally yours,


Howard Garrett
The Dirt Doctor
  


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