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Gypsy Moth and Winter Moth


Gypsy Moth caterpillar feeding on oak.

Gypsy moth caterpillars appear in early May to mid and feed until the first week of July. They may not be much noticed for the first few weeks but about early June they begin spinning down from trees and migrating to different trees. It is at this time that they can really be a nuisance. As they grow, appetite increases to the point when mid to late June comes around one might wonder what happened to their landscape. Gypsy moth caterpillars eat just about anything green. So don't be surprised when you see them in the shrubs and trees that had not been attacked before.

I use the safest products available. For these caterpillars, I use Conserve, active ingredient Spinosad which is organic. This product is very effective and completely safe for all mammals, birds, reptiles, amphibians etc. It is made from a bacteria and has a unique mode of action that only affects insects. As such, it carries no caution label which almost unheard of. Also, I have a powerful sprayer and can reach the tops of our tallest trees.


Here there are both male and female Gypsy Moths present. The females produce strong pheromones to attract t​he males. Shortly after they lay eggs in the buff colored masses visible here. Then, shortly thereafter, the females and later the males die.​


Here is a closer view of Gypsy Moth mating and egg laying activity.​



The Winter Moth female is flightless.

The Female Winter Moth lays her eggs along the trunk and around branch unions of trees and shrubs. This occurs in November and December and occasionally into January. The eggs lay dormant until very late winter when the larvae inside begin to grow.

Why My treatment is better

Timing is everything with Winter Moths. Unlike most companies, I only spray the most organic products at optimal times. Because the eggs do not begin to develop until mid-March, Dormant Oil sprays are not as effective when sprayed before the very end of March. Virtually all companies spray too early.

Since the mode of operation of Oil is suffocation, I wait until just before the larvae hatch and have a higher requirement for oxygen. The difference between spraying during the first week of April mid-March, when most companies begin spraying, is profound. The eggs hatch about the seventh of April, depending on the weather. Once the eggs hatch the larvae are vulnerable, for several days, to the same Dormant Oil that kills the larvae. Trees sprayed at just the right time exhibit almost no insect damage.

What is Dormant Oil

Dormant Oil is a type of paraffin wax and is not toxic. Even so, I use a superior type of oil called Summer Oil. Summer Oil is an even more refined form of Dormant Oil. The specific type of oil I use is called Purespray Green and is certified organic. Oils do not leave a harmful residue and are very effective in controlling many insect pests.


Shortly after they hatch some Winter Moths extrude a thread into the wind and drift along to nearby trees. This is why trees need two sprayings. The second time is when the buds start to open. Larvae squeeze their way into the expanding bud where they are protected from predators. This makes them difficult to control since spray cannot reach them until the leaves begin to open.  

Second Treatment: BT or Conserve

Once the leaves have begun to open then the second treatment must be made quickly, before the larvae have grown. At the larvae are too big for oils to be effective so the least toxic product is called Conserve SC which active ingredient is Spinosad. Spinosad is produced from a bacteria that was found here in Massachusetts. It is absolutely unique in of action in that it targets a part of the nervous system that is unique to some insects. Spinosad is organic in that it is naturally developed by fermentation of bacterial waste.

a Bacteria, Bacillus Kurstaki (BT) is effective once the leaves have if there is no rain predicted. The problem with BT is that it is must be ingested by the caterpillar to be effective. When they first hatch they enter the newly emerging bud and cannot be reached until the bud opens.

Winter Moth Predator

Cyzenis is a Tachinid fly that parasitizes winter moth is a Tachinid fly that parasitizes only the winter moth. This small fly was released in Falmouth is 2007. It has yet to be effective although it is said to have established itself here.

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