Winter and Gypsy Moth

By Organic Lawn Care
Winter Moth caterpillars hatched two to three weeks ago and have been quietly turning the young leaves of their favorite trees into Swiss cheese. The caterpillars are now getting to the size where the damage will increase very quickly.

Gypsy Moth caterpillars began hatching this past week in East Sandwich. They are still very young and now is the perfect time to control them before the damage is done.

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2015 was an active year for Winter Moths and Gypsy Moths.  These caterpillars left large areas of Cape Cod and the South Shore defoliated.  Healthy trees and ornamentals can usually tolerate a season or two of defoliation, but repetitive defoliation can lead to tree mortality. Trees that were damaged last season should be protected from defoliation by caterpillars this season.  Special attention should also be paid to proper watering and fertility to maintain plant health and vigor.  So, with this in mind, what is the outlook for this year?


Winter Moth:  Tiny caterpillars usually hatch in mid to late April and immediately seek out the buds of their host plant and begin feeding, many times prior to bud break.  Once the bud opens the caterpillars will usually continue to feed through May and sometimes into early June.  The Winter Moth is a green inchworm that feeds on a wide variety of deciduous plants.


Gypsy Moth: Gypsy moth caterpillars are also green early on but turn brown after a couple weeks.  They typically hatch in early May and are most destructive in June when they become large. Gypsy Moth will consume a wide variety of plant material including evergreens such as White Pine and Spruce.


Prevention and Control – There is no effective way to prevent either of these caterpillars from hatching and potentially causing damage to your ornamental and shade trees. The only effective treatment is to protect the leaves with carefully timed insecticide applications.


For Winter Moth we typically recommend 2 treatments and a 3rd treatment may be necessary if gypsy moth is present. The first will coincide with the hatch of the caterpillars and the bud break of their favorite hosts (late April-first week of May).  A second treatment, 10-14 days later is necessary for three reasons:


1.  Do to our many micro-climates on Cape Cod there is an extended hatch period making the timing of the first spray a bit of a guessing game.


2.  The young caterpillars hang down on silken threads to be blown with the wind to infest new areas far away from the hatch site.  This process is called “ballooning”.


3.  Various host plants do not all break buds at the same time.  Therefore, many trees haven’t broken bud yet and the leaves may be left unprotected by the first treatment.