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WANTED FOR: STRIPPING TREES OF LEAVES AND FRUIT, CAUSING UNSIGHTLY INJURY

Winter MothWinter Moth

Aliases The Munch' Inch Worm; Operophtera brumata

Description
Hangout: Ornamental, orchard and forest trees, especially oaks and maples
Physical Features: Young are green inchworms (up to 1" long) with racecare white stripes on sides: adult males are grayish brown with 1" wingspans, and appear hairy; females have no wings

Life Cycle
Winter moth larvae hatch and feed ravenously on leaves and fruit beginning in early spring. Larvae feed on the inside of buds and leaf clusters during the day, inching their way to the outside of leaves at night. In June, larvae drop to the ground under the trees where they bury themselves in the soil until fall. November through January, adults come out and mate. Having no wings, females have a grueling climb up tree trunks where they lay eggs.

CAUTION
WET SUMMERS AND MILD, MOIST AUTUMNS ARE FAVORABLE TO WINTER MOTHS AND MAY INCREASE THEIR POPULATIONS DRAMATICALLY.
Crunch the Munch!

1. Patrol the area

  • In early spring, stake out favorite daytime hangouts like inside buds and leaf clusters. At night use a flashlight to look for dubious characters on the outsides of leaves.
  • Search tree trunks for wingless females in October through January.
  • Look for devastated flower buds and early dropping of petals from fruit trees such as cherry trees.
  • Keep a record of what you see and what you don't.

2. Make a positive I.D.

  • These caterpillars should be one of the only typical-looking inchworms around in early spring.

3. Do a thorough background check

  • Figure out which stages of the winter moth lifecycle you can impact. If you're anxious to get into the yard during the winter, search out females on warm, winter evenings. These wingless females are easy to catch. Look for the cloud of male moths around the tree trunk waiting for a chance to mate.

4. Determine the danger level

  • As with most pests that cause leaf loss, established trees can bounce back from up to 25% leaf loss for one or two years repeatedly.
    Consider that winter moth is a cyclic criminal. It's here one year, gone the next.

5. Make a plan

  • Do-Nothing Method
    -If the danger level is low enough, this is a good strategy. Remember to consider the health of your tree and its ability to withstand some leaf loss. -Trees that have been established for more than a couple of years are quite able to defend themselves. Don't feel like you have neglected your tree if you decide not to do anything. Winter moth is subject to many natural predators and parasites.
  • Manipulative Measures
    -S.W.A.T. time! Search and destroy is the name of the game. Caterpillars and wingless females are the easiest to annihilate.
    -Your tree can defend itself if it's strong and healthy. Check with Cooperative Extension if you aren't sure how to water or fertilize your tree.
    Roadblock female winter moths on their way to mate and lay eggs. Put a 3-4" wide sticky barrier on tree gauze around the trunks of infested trees. Both the sticky stuff and gauze can be bought at garden stores for less than $10.
  • Secret Agents
    A gang of killers has increased its numbers in recent years and they are hungry for winter moth larvae. They are parasitic flies that trick winter moths into eating their eggs by placing them near recently munched on leaves. As the egg hatches inside the winter moth, it literally eats the moth inside out.
  • Armed and Dangerous
    -Suffocate winter moth eggs by applying dormant oil to your tree, purchased from home and garden stores, during November through January. Follow the label directions carefully to prevent scalding leaves.
    -Bacillus thuringiensis (B.t) is deadly to caterpillars, yet it's less toxic to other wildlife than most insecticides. It works best on young caterpillars, so spray in early spring on a cloudy but warm day. (Sunlight breaks down B.t.) -Look for products in home and garden stores that contain B.t. and are registered for use on caterpillars.
    -Don't forget to read and follow directions for use, storage, and disposal, whenever a chemical is used.

6. Evaluate the results

  • To improve your ability to ward off this criminal, keep a record of which trees were victimized by winter moth, what the percentage of leaf loss was, and if there were any casualties. It's also a good idea to take note of the victims' health prior to the attack, since healthy trees usually bounce back.

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For more information, contact Scarlet Tang or Todd Murray
WSU Cooperative Extension (360) 676-6736
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