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Winter Moth Caterpillar Infestation

 Winter Moth Caterpillar Infestation

Tree Insect Control – Winter Moth Caterpillar Infestation

If you live along Northeastern Seaboard chances are you have or will have tree damaged by a small, green caterpillar called the winter moth (Operophtera brumata), a member of the Geometridae family.

Winter Moth Caterpillar

The Winter moth is an insect pest that was introduced to North America from Europe. Its introduction has been known for years in various regions of eastern Canada, including: Nova Scotia, Prince Edward Island, and parts of New Brunswick.

Susceptible Trees

Any property that has deciduous trees such as – oak, maple, cherries, birch, beach, and ash are susceptible to the, nasty leaf crunching, Winter Moth Caterpillar.

What Does the Winter Moth Caterpillar Look Like?

Winter Moth caterpillars look a lot like an inchworm. They are small, green, approximately 1-inch long, and have a faint white longitudinal stripe running down both sides of the body.

The Winter Moth caterpillars emerge in the spring time when the leaves begin to bud and open up, feeding on both flower and foliage buds.  T

Life Cycle

The Winter Moth Caterpillar will feed voraciously until mid-June, when they migrate to the soil and bury themselves for pupation. They will stay in the soil in the pupa stage until they emerge in late November as adult moths.  The cycle continues, in the fall, when the moth lays eggs for next springs caterpillars.

Winter Moths emerge from the soil usually mid-late November and may be active into January whenever the air temperatures are mild (usually above freezing).

Females moths are usually found at the base of trees or scurrying up tree trunks, but can be found almost anywhere. After mating, the female deposits loose eggs on bark, in bark crevices, under bark scales, on lichen, or elsewhere. The adult moths then die and the eggs over-winter. Eggs are green at first, but turn red-orange soon thereafter. In March, just prior to hatching, the eggs turn a bright blue and then a very dark blue-black before hatching. Eggs hatch when temperatures average around 55º F

Deciduous plants vulnerable

• Oaks
• Maples cherries
• Basswood
• Ash
• white elm
• crab apple
• apple
• blueberry
• Sitka spruce (Scotland)
• heathers (England)
• roses and herbaceous perennials that are located beneath or near infested trees

Winter Moth Caterpillar Video

The Decision To Treat Or Do Nothing

When deciding what to do, 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 able to defend themselves.  Established trees can bounce back from up to 25% leaf loss for a year or two.

Keep in mind that, if left untreated, these caterpillars can create huge defoliation and may cause irreparable damage to the tree.

Non Chemical Management

If your tree suffered heavy defoliation by winter moth caterpillars, water will be critical for the tree to have a second flush of leaves.  Supplemental watering is necessary throughout the growing season and the application of fertilizer is not recommended.

Dormant Oil

A November to January application of dormant horticultural oil has shown some success with the Winter Moth.

Tree Banding

Tree banding, [applying a heavyweight, sticky paper to the tree] has been successful as a barrier to climbing caterpillars, or for the climbing adult female moths in late fall to early winter.

Two Chemical Treatments

Spinosad, an active ingredient in many tree and shrub insect control, works well against winter moth and most other caterpillars.  Spinosad is fairly gentle to other organisms, such as the parasites and predators.

Bee NoteSpinosad is “highly toxic to honey bees at the time of application” and, therefore, great care should be taken to protect honeybees during application.  Avoid spraying crabapples, or other flowering trees, when in bloom and bees are foraging. Once an application of Spinosad has dried, the threat to bees drops significantly.

Don’t forget to read and follow directions for use, storage, and disposal, whenever a chemical is used.

How To Chemical Treat The Winter Moth

Late this May, I found a Winter Moth infestation in my ornamental Cherry tree.  After identifying the caterpillar I designed my tree treatment in a two-prong approach:

1. Spray application
2. Soil treatment

ID Tip: Put a caterpillar in a plastic bag and bring to a nursery for identification.

Spray On Application

A spray application is applied directly to the tree and leaves and targets the active caterpillars.

I purchased a spray application that was rated for organic gardening [fruit trees, vegetables and ornamental trees] and had the 0.5% chemical Spinosad.

The spray comes in a container that attaches directly to your hose.  Water propels the chemical onto the tree leaves and the spray container automatically dispenses the chemical at the proper mixture.

These sprays act immediately to kill the caterpillars but can be washed away by rain.



Spray On Application Steps

  1. Attach spray container to hose and turn on hose
  2. Turn spray container to either spray or stream
  3. Spray and saturate the tree and leaves.
  4. Spray in an even coating and try to avoid over spraying other trees and areas


Soil Treatment

Remember that the caterpillar drops to the ground for the pupa stage, prior to turning into moths.  This treatment is applied to the area where the caterpillar drops and is intended to be absorbed by the tree roots.

I purchased a insecticide root control in concentrate with 1.4% active chemical Imidacloprid.  Imidacloprid is an insecticide that was made to mimic nicotine. Nicotine is naturally found in many plants, including tobacco, and is toxic to insects.

Bee NoteImidacloprid is not very toxic to birds and slightly toxic to fish, although this varies by species. Imidacloprid is very toxic to honeybees and other beneficial insects. The role, if any, of imidacloprid in Colony Collapse Disorder is not yet clear.

This treatment is applied to the soil from the tree trunk out two feet. The insecticide moves through the root zone and up through the tree providing protection from insects. It will also protect new growth which the tree will need to re-leaf.

I like this application because once in the root system and tree it cannot be washed away be rain like the spray on application.

Soil Application Steps:

  1. Determine the amount of product to apply by first measuring the circumference of the tree trunk at chest height, or 4.5 feet from the soil.
  2. You can use a flexible measuring tape, ribbon or string to wrap around the tree.
  3. Mark where the ribbon or string meet
  4. Measure it with a standard tape measure.
  5. I used a piece of printer paper to wrap around the tree trunk.
  6. Follow the manufacturers directions exactly to determine mixture.
  7. On my application the product called for a mix of 1 ounce per inch of tree circumference.
  8. I mixed my solution in a 5-gallon pail marked into 5ths.
  9. I followed the directions for a tree circumference of 11-inches, applying my mix to one gallon of water. [Smaller tree application]
  10. I applied the solution to the root zone as a circular band around the base of the tree.
  11. Work your way around the tree outward for 2-feet.

TIP – do not irrigate right away.

It may take a week to three months, depending on tree size and vigor, before insect control is achieved.  This product can be applied yearly, spring to early fall. Do not apply to frozen water logged soil



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