What are Those Little Green Worms Hanging from Oaks Trees?

Article by Rick Orr
APL Lawn Spraying Inc.

Rick Orr is the creator of Iloveturf.com, an Agronomist and the Owner/Operator of APL Lawn Spraying. Rick is a graduate from VA Tech in Agronomy (Turf Ecology). He has been a Golf Course Superintendent, Certified Arborist, Landscape Contractor, Irrigation Contractor and Adjunct Professor for Environmental Horticulture.

Rick is an expert at growing St Augustine turf. Since 1995, Rick has spent his time researching, developing and testing the best management practices for St Augustine turf grown in Pinellas County.

The results of that work is a one of the top rated lawn spray companies in Pinellas County – APL Lawn Spraying. APL Lawn Spraying is a family owned business serving residential and commercial properties in Pinellas County, FL.

APL Lawn Spraying provides lawn spraying to commercial properties, HOA’s and single family homes. To request a free quote for your property, click here: Free Advice or Price Quote

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Grab your hats, East Coast — the worms are back

Ahhh, spring! The sky is clear, the sun is out, and after many months of long underwear and wool coats, perfect strangers once again feel compelled to comment on the Donatello tattoo on your bicep (Ninja Turtle, not Renaissance sculptor). If you live on much of the Eastern seaboard, there’s another spring ritual to look forward to: WORM SEASON!

A few years ago, East Coasters started noticing something strange: All of a sudden, there were tiny green inchworms everywhere. Seemingly over night, these worms became as ubiquitous as the bright yellow pollen that coats every house, car, road, and sinus cavity like eraser chalk come April. Millions (maybe billions) of tiny worms with waggling heads and an awful lot of legs were falling from the trees and parachuting onto people’s heads. They covered roofs, porches, picnic tables, garden beds, and shrubs. They hung from your Labrador’s ear and landed in your sweet tea. People waved sticks in front of their faces to break worm silk dangling from tree limbs. It was an invasion. And it’s back.

A quick Google search of “nasty green worms in springtime” reveals these pests are actually called cankerworms. And pests they are. Cankerworms are a type of caterpillar that lays eggs in the fall. Come spring, their eggs hatch into ravenous little offspring that will literally eat every leaf in your neighborhood (and quickly — a swarm can eat the canopy off an oak in just two days). This is obviously not good for trees, but it’s also bad for people: Imagine a July with all the heat and none of the green foliage that makes summer somewhat bearable, or, if not bearable, at least pretty. If cankerworms are left unchecked, we could see a summer with no shade. Shudder.

So how’d these little guys end up taking over the East Coast? They aren’t talking, but we know that the problem is made worse by the lack of biodiversity in urban areas. According to North Carolina State University professor Steve Frank, “Cankerworms did more damage in simple urban environments, where the understory consisted of only a few shrubs, than they did in more complex environments with greater plant diversity.”

And while we don’t know exactly if climate change has anything to do with the booming population of these little monsters, Michael Waldvogel, another professor in NC State’s Entomology Department, told me that insect growth is accelerated in urban heat islands. In other words: Cities, you’re screwed.

Or maybe not. Municipalities with large invasions have tried tree banding, which basically means that you wrap a garbage bag around tree trunks and hope that prevents the worms from crawling into the canopy. This works better than pesticides, Dr. Waldvogel told me, although it also makes your trees look like homeless guy at my bus-stop who wears a Glad bag around his waist. Still, a small price to pay to keep these little green bums from eating all your foliage, right?

Beyond killing trees and hitching rides on your head, these worms have another disturbing habit, which I discovered one night last spring. I was living in Charlotte, N.C., at the time, a city that has been especially hard-hit by cankerworms, and a friend invited me over to her house for a bonfire. “Bring a hat,” she said. That seemed weird, but it made sense when I got there and saw that the fire pit was located directly underneath a stand of willow oaks — the cankerworms’ meal of choice. There was so much worm shit dropping from the trees that it actually sounded like it was raining. After that night, I started taking walks in full riot gear.

Since my last cankerworm spring, I moved from North Carolina to Seattle, and on days in April when I’m still wearing long underwear and I’ve forgotten what it’s like to have dry feet, I think, yes, it may be raining, but at least it’s not raining worm shit. Enjoy spring, East Coast! You may want to spend one of those glorious April afternoons banding your trees.

What’s that caterpillar hanging from the tree?

Your clients may be asking you about these critters. They are the larvae (caterpillars) of either oak leafrollers or oak leaftiers, two different species of moth. Leafrollers are from the genus Archips and leaftiers are from the genus Croesia.

This larval or caterpillar stage is one part of the moth’s life cycle. The adult stage is a yellow to light tan colored moth with a wingspan of 12-25 mm. Moths lay their eggs on the small branches of host trees in the late spring. These eggs hatch early the following spring when the oak leaves began to grow. Larvae feed and grow for about one month and then drop to the ground to pupate. Moths emerge within two weeks. Females live for a few days and lay up to 100 eggs. Then we see nothing more of these insects until the following spring.

What is important about them? They can cause widespread and severe defoliation (loss of leaves) of the trees they feed upon, but this rarely happens in Florida. The common scenario is several years of light to moderate defoliation, then insect populations collapse and we are unaware of these insects for a number of years. They can also be a nuisance to humans, but they are harmless.

Is there any control for the caterpillar? Natural controls (predators, parasites and diseases) usually keep these caterpillar populations at low levels. Mockingbirds and other birds feed on the caterpillars, and wasps appear to be the best control. For high-value trees or where caterpillar populations are especially damaging try using a biological control spray of Bacillus thuringiensis var. kurstaki. An insecticidal spray containing carbaryl (Sevin®) can be used as a last resort (this should be applied by a pest control operator). The ideal time for applying an insecticide is just before the insects begin their last week of voracious (heavy) feeding.

by sfylpinellascounty

Posted: March 9, 2011

Category: Home Landscapes, Pests & Disease

Winter Moth Identification & Management

Pest: Operophtera brumata

Order: Lepidoptera

Family: Geometridae

Host Plants:

While oak, maple, and apple are preferred hosts, many other deciduous plants are susceptible to damage from winter moth caterpillars. These include but are not limited to: cherry, basswood, ash, white elm, crabapple, and blueberry. Winter moth caterpillars may also drop or ‘balloon’ onto nearby plants like roses, herbaceous perennials, annuals, etc. that may be found near or beneath infested trees. Winter moth caterpillars are not usually found feeding on evergreens or broad-leaved evergreens, although they have been found on certain spruces such as Sitka spruce (Europe), and heathers (Scotland). Partial defoliation can be the norm for this species. Damage to blueberry and apple crops is especially severe as the reproductive parts responsible for fruit can be destroyed before buds open fully.


Winter moth is a non-native insect that was identified in Massachusetts in 2003, through the collaborative efforts of Deborah Swanson, Horticulturist, UMass Extension/Plymouth County Extension (retired), Hanson MA, the late Robert Childs, Entomologist, UMass Extension, Dr. Joseph Elkinton, Entomologist, UMass, Amherst, MA, George Boettner, Lab Manager in the Dept. of Environmental Conservation at UMass, Amherst, MA, Dr. David Wagner, Entomologist, UConn, Storrs, CT and Richard Hoebeke at Cornell University, Ithaca, NY in 2003.

Winter moth was initially introduced from Europe to North America via Nova Scotia in the 1930’s, where in the 1950’s it became a serious pest in parts of eastern Canada (Nova Scotia and Prince Edward Island). It was then introduced separately to western Canada around 1970, where it became a problem in Vancouver, British Columbia. In the1950’s, Winter Moth was also found in the western United States of Oregon and Washington, where it warranted control measures primarily in commercial blueberries. Outside of Oregon and Washington states, prior to its discovery and identification in Massachusetts in 2003, winter moth was not known to be a significant pest in any state in the United States. See Winter Moth in Massachusetts: History and Biological Control for more information.

Life cycle:

Moths (the adult stage of winter moth) emerge from pupae in the soil usually in mid-late November (usually before Thanksgiving) and may be active into January, whenever the air temperatures are mild (typically when above freezing). The small (0.79-0.98 inch wingspan) male moths are light brown to tan in color and all four wings are edged with small elongate scales that give the hind margins a slightly hairy or fringed appearance. The male moths are strongly attracted to lights and can often be found flying around outdoor lamps or holiday lights. The female (0.31 inch) is gray, almost wingless (brachypterous) and, therefore, cannot fly. She emits a sex pheromone that often attracts clouds of male moths. Females 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, etc. Each winter moth female may produce 150-350 tiny eggs, which are very difficult to see. The adult moths then die and the eggs over-winter. Eggs are green at first, but turn red-orange soon thereafter. In March, prior to hatching, the eggs turn a bright blue and then a very dark blue-black just before hatching. Eggs hatch when temperatures average around 55º F. It is believed that egg hatch in Massachusetts occurs when 20–50 Growing Degree Days1(base 50º F) have accumulated, which can be anywhere from late March into early-mid April, depending on the year and the location. (The Elkinton lab at UMass, uses a base 40º F when completing Growing Degree Day calculations for this insect and suggests that hatch occurs between 177 and 243 GDD (base 40°F).2)

In most years, egg hatch occurs just at, or right before, bud break of most of the host plants and delayed bud opening due to cool weather can lead to caterpillar death. The newly hatched caterpillars crawl up tree trunks and wriggle between bud scales of newly swelling buds of such hosts as: maple, oak, ash, apple, crabapple, blueberry, and cherry, etc. and begin feeding. Winter moth caterpillars cannot chew their way through closed bud scales, but as the bud scales open, the caterpillars can scrape away at the soft leaf tissue below, producing bullet-hole like damage to the leaf, even before it fully expands. The young larvae also produce strands of silk, which make them air buoyant and this larval dispersal method is known as “ballooning” (like bungee jumping, but not staying tethered to the point of origin). In certain situations, given topography and wind patterns, ballooning winter moth caterpillars can arrive in areas where they have not been expected to be a problem.

The caterpillars feed in both flower and foliar buds and, once a bud has been devoured from within, the caterpillar will migrate to other buds and repeat the process. Destruction of the flower buds leads to greatly diminished harvest on fruit crops such as apple and blueberry. After buds open, the small caterpillars can be found within the tight clusters of new leaves and flowers during the day. During cool springs, if weather hinders leaf expansion but bud scales have begun opening, the winter moth caterpillar can cause high levels of foliar injury as they are protected from insecticides while inside the buds. Winter moth caterpillars often leave foliar clusters to become free feeders at night. Older larvae feed in expanding leaf clusters and are capable of defoliating trees and other plants, when abundant. At maturity, the caterpillars will be approximately one-inch-long, whereupon they drop to the soil for pupation. Pupation occurs in late May/early June depending on the geographic location. Areas including Cape Cod are often a week or two behind inland locations.


Winter moth caterpillars are very tiny when newly hatched, less than the size of an eyelash and they are blackish in color at that time. As they feed and increase in size, they are pale green with a faint white longitudinal stripe running down both sides of the body. They are “loopers” or “inchworms” and have just two pairs of prolegs. Winter moth caterpillars are often found in association with both the fall and spring cankerworms, as well as Bruce spanworm (Operophtera bruceata), which are very similar in appearance and have similar feeding patterns to that of the winter moth caterpillar. Fall cankerworm caterpillars have “2 and ½” pairs of prolegs: two pairs of the prolegs are longer than the third, much shorter pair which is counted as number 3 when starting your count from the rear end of the caterpillar. Bruce spanworm is native to the Northeast and is rarely a problem. However, the males of this species are attracted to the pheromone used in winter moth traps and thus create a challenge for researchers to discern the difference between the males captured in these traps given their remarkably similar appearance.


Treatment for the Eggs:

Horticultural oils work by suffocation and can be effective on insect eggs. Oils must cover the target organism at the time of application or no insecticidal effects will result.

Given that many winter moth eggs are exposed on the bark, the potential to manage them with a horticultural oil spray exists, however, it is probably not practical for ornamental landscape trees, as eggs that are protectively hidden within crevices and under lichen will not be covered by the spray and killed. In years of heavy winter moth pressure, oil sprays will most likely only achieve limited results; eggs are deposited virtually everywhere on trees and shrubs and new caterpillars will quickly migrate from untreated areas to the oil-treated plants via ballooning.

Dormant oil spray applications are mostly recommended for blueberry and apple growers and not so much for landscape operations where protecting the flower buds is not as essential as it is for commercial or home fruit growers. Some growers add a chemical companion, such as spinosad, to the oil spray to reach newly hatched caterpillars whose eggs were not covered by the oil. However, it is extremely important to know what can and cannot be mixed with oils and then applied to specific plants. This method is best left to the professional licensed applicator and not the homeowner as mixing compounds that should not be used together can cause serious injury to plants, the environment, and the applicator. Always check to be certain that any two pesticides are compatible for tank mixing by reading the label or consulting with the manufacturer of the pesticide(s).

Typically, dormant oil sprays are applied in the very late winter or very early spring depending on temperatures and host plant phenology. When applying oil sprays, it is prudent to have temperatures above 45°F and to avoid applying oil when temperatures may dip below freezing for 24-48 hours after application. Temperatures below this threshold greatly increase the risk of causing injury to the plant (phytotoxicity). Certain weather conditions, such as when it is cool and cloudy, can also delay drying time and enhance the potential for injury.

Oil sprays are sometimes applied in the fall to manage certain insects, but it is of no use for winter moth given that the eggs do not appear until very late fall and into the early winter.

Treatment for Free-Feeding Caterpillars:

In spring (early – mid-April), monitor expanding tree buds and developing leaves for winter moth caterpillars on susceptible trees and manage early, if present. Managing winter moth caterpillars when they are small will often result in reduced foliar damage. Winter moth caterpillars are active from April until late May or early June, whereupon they drop to the soil and almost immediately spin a cocoon and pupate.

(see Fig_6 through 9) Once the buds open, the larvae are known as “free-feeders” given that they are now on the foliage and free to move readily from one area to another. As “free feeders”, winter moth caterpillars are exposed and very treatable with a variety of products. Particularly with ornamental plants, it is best to wait until leaves have fully expanded before applying the below active ingredients. (As mentioned earlier, in crops such as blueberry and apple, this is not the case.)

1. Spinosad: This active ingredient is derived from a bacterium that is subjected to a specific fermentation process to develop the active ingredient(s) for the insecticide commonly known as spinosad. It works on the insect nervous system in a novel manner and can be effective as a contact spray as well as by ingestion.

A. Spinosad is a biorational insecticide and can also be referred to as a microbial pesticide. Biorational insecticides are materials that are relatively non-toxic to people with few environmental side effects, particularly when compared to chemical insecticides discussed below.

B. Spinosad products work well on caterpillars of all ages, even caterpillars known as sawflies, which are the larval stage of certain wasps in the order Hymenoptera.

C. Although fairly safe by not harming parasites and predators, the label does warn that spinosad can be “highly toxic” to bees at the actual time of application. Once the spray has dried, however, the toxicity to foraging bees is much reduced. An example would be to not spray for winter moth when crabapples, or other flowering trees, are in bloom and bees are foraging.

2. Bacillus thuringiensis (kurstaki), also commonly known as B.t.k: This product is a bacterium that is specific to lepidopteran larvae (butterfly and moth). It must be ingested to be effective. Once inside the gut, this bacterium becomes activated and multiplies. By going through a somewhat complicated biological process, this product will eventually form toxins that become lethal to the caterpillar. A few notes about its use:

A. B.t.k. works best on the younger instar stages of caterpillars; older ones are much less affected.

B. This product fits well into any IPM program, in that it does not impact the environment, harm the applicator nor does it affect beneficial organisms such as predators and parasitoids, when used as directed.

C. If applied while the buds are still expanding, any new foliage that emerges in the days after application of this product will not be protected.

D. Caterpillars that ingest B.t.k. will stop feeding almost immediately however they may not die for 1-3 days. It is often disconcerting to still see live caterpillars days after treatment but even though they may be moving, they are not feeding.

E. Although some may be concerned about B.t.k’s effect on native Lepidopteran species, it usually poses a limited negative effect given the relatively small areas being treated (e.g. individual trees and not entire forests).

3. Chemical Insecticides: Although many of the organophosphate (e.g. malathion, acephate) and carbamate (e.g. carbaryl,) insecticides are now unavailable or limited in use, a few still exist. Mostly, when considering the chemical insecticide option (over a biorational or microbial insecticide) the more conservative chemical choices now are the pyrethroids, which can range from toxic to highly toxic (depending on the product) to bees and other insects, even after they dry. Do not spray plants when they are in bloom. In general, they would be applied at egg hatch, although timing is difficult. They are mostly used against the free-feeding caterpillars once the buds have opened. In general, pyrethroids have a “knock-down” effect by killing the target organism quickly. They then break down into inert ingredients, sometimes within a matter of days. This, however, varies depending on the specific pyrethroid product used and the conditions that it is subjected to after application (e.g. weather, temperature, added stickers, etc.) and some can persist for longer periods of time in the environment. In general, these chemical products tend to be much harsher on the beneficial organisms and should be used thoughtfully. Some pyrethroid products are restricted use. Always consult your local supplier and always read, understand, and follow all label directions for pesticide products.

4. Insect Growth Regulators: Also known as IGR’s, active ingredients such as tebufenozide mimic the hormone ecdysone, which is commonly referred to as “the molting hormone” and ingestion of this product prevents the caterpillar from molting (shedding its exoskeleton and forming another in order to grow) and it dies. Tebufenozide is only effective against lepidopteran caterpillars and will not work on sawfly caterpillars. Tebufenozide is considered to be a very effective tool for the IPM approach to managing winter moth caterpillar, however it still has environmental implications including but not limited to toxicity to aquatic organisms and ground water protection concerns as it has properties and characteristics similar to chemicals detected in ground water. For all insecticidal products, always read, understand, and follow label instructions.

A guideline of not applying insecticides to flowering plants is important to follow when considering using chemicals that are toxic to pollinators. Other actions an applicator can take to preserve pollinators can also include the timing of application (after bloom or times of day when pollinators are less likely to be active) and choosing least toxic active ingredients with shorter residual action. Certain product formulations may be more likely to impact pollinators (dusts, wettable powders, and microencapsulated products may cling more readily to the bodies of foraging bees). Treating at temperatures where bees are less-likely to be foraging (for many, that is below 55°F) or cooler times of day can be best for avoiding interaction with these beneficial insects.

With any chemical or biorational management option that kills winter moth caterpillars, there is also a chance of killing Cyzenis albicans, which may be parasitizing those caterpillars if management is implemented within biocontrol release sites and the surrounding areas where Cyzenis albicans is currently spreading on its own. Management should focus on killing eggs of winter moth (dormant oil sprays) where practical (such as in blueberry crops or very small landscape plants) or limit sprays to biorationals such that can target early instar (younger) caterpillars where possible, to prevent killing C. albicans larva in the later instar (older) caterpillars and pupae. However, if a smaller number of host plants are treated, as can be typical in a landscaped situation, the impact to C. albicans may be low and this biological control organism will still have winter moth available in nearby forested areas to utilize during its lifecycle.

Treatment for Winter Moth Pupae in the Soil:

There are virtually no controls for this pest in this life stage other than natural predation by such organisms as ground beetles, small mammal predators (especially shrews), and wasp predators.

Winter moth caterpillars drop from their hosts to the soil to pupate around late May/early June in Massachusetts and remain in the soil until the adults emerge roughly around mid-November. Anyone doing fall transplants, renovations, or cleaning up garden beds near winter moth host plants that have had issues with this insect should be aware of the risks of accidentally transporting winter moth pupae that may be present within these soils.

Treatment for Adult Winter Moths:

There are no control options for the adult stages of these moths. They do not feed in this life stage.

Banding Trees:

Some products are available and are advertised that the bands act as a barrier to climbing caterpillars, and/or for the climbing adult female moths in late fall to early winter. This method is known as “tree banding”. The products for tree banding are generally heavyweight paper or plastic strips that are covered with a sticky substance that snare climbing caterpillars or female moths. However, field observations do not necessarily support the effectiveness of tree bands for reducing winter moth populations when in high numbers and they are therefore not recommended for that purpose.

Using Trees Bands to Monitor Egg Hatch for Managing Winter Moth Caterpillars:

Trees bands, however, have inadvertently been found to be useful for monitoring winter moth egg hatch in the spring. In late October, place a band around the trunk of an oak, maple, or apple tree that has a history of winter moth damage. (Place, or wedge, cotton or polyester fiberfill under the band to prevent the small female moths from going under the band and continuing their climb up the tree.)During peak winter moth population years, individual sticky bands may fill up with adult moths within an hour. In some cases, it has been witnessed that female winter moths, upon approaching the barrier bands, often lay their eggs on the tree trunks just below the barrier and/or crawl over or under the barrier and lay their eggs just above. The eggs are often laid in a circle above and below the band and can be seen with a magnifying lens.

To monitor for winter moth egg hatch in late-March to early to mid-April, go out and look around the bark directly above or below the bands to check if the eggs have changed color, or are about to hatch, using a hand lens or other magnification. Eggs that are still orange-red are not yet ready to hatch, whereas those that are turning blue are very close to hatching. The observation of the timing of egg hatch may aid in the planning of chemical management options, particularly in crops such as blueberry and apple, where the insecticides must be applied prior to winter moth caterpillars wriggling their way into flower buds to feed.


Winter moth is a very serious insect pest. Over the past 15+ years it has caused significant damage to and the decline of many trees, in eastern MA, especially southeastern MA and on the North Shore. Many deciduous trees (primarily oak) are displaying signs of serious decline given the multiple consecutive years of defoliation by winter moth, frequently in combination with forest tent caterpillar and gypsy moth.

Within the past several years, many trees (mostly oak) have died in southeastern Massachusetts from the stress of this defoliation coupled with drought and other factors. Several years of defoliation often weakens trees to the point where secondary agents (sometimes known as ‘weak invaders’) can overcome what is left of a tree’s natural defenses (due to repeated defoliation) and kill the tree. Such secondary invaders include: wood borers, bark beetles, Armillaria (shoestring root rots) and others.

Research in Canada has shown that four consecutive years of partial defoliation of deciduous hosts can lead to branch mortality while complete defoliation in each of those years leads to tree mortality. In certain regions of Nova Scotia, this pest was responsible for 40% red oak mortality in forested stands in the 1950s before biological control by Cyzenis albicans became widespread in the early 1960s. Since that time, winter moth has been mostly a non-pest in Nova Scotia.

Additional information:

1Growing degree day information is available in the Landscape Message for areas throughout Massachusetts, using a base 50ºF. For more information on how to calculate growing degree days, please visit this fact sheet.

2The Elkinton lab at UMass uses a base 40º F when completing Growing Degree Day calculations for this insect and suggests that hatch occurs between 177 and 243 GDD (base 40°F, January 1 start date, double sine method). Resources such as uspest.org will allow you to manipulate how GDD’s are calculated, including using a base 40ºF and different mathematical models. The reason for using Base 40 is that 40ºF is very close to the minimum temperature for winter moth development and considerable GDD accumulation occurs between 40-50ºF. Predicting hatch with GDD is imperfect for this insect, however. Research in the Elkinton lab and in Europe has shown that later springs with older eggs require fewer GDD to hatch.

Winter Moth in Massachusetts: History and Biological Control: fact sheet for information on the history of winter moth in Massachusetts and Dr. Joseph Elkinton’s (of UMass) research on the biological control of this insect.

Written by: The late Robert Childs, Entomologist, UMass Extension, Deborah Swanson, Horticulturist, Plymouth County Extension (retired), and Joseph Elkinton, Professor in the Department of Environmental Conservation at UMass Amherst with Recent Updates from Tawny Simisky, Extension Entomologist, UMass Extension Landscape, Nursery, & Urban Forestry Program, Deborah Swanson, Joseph Elkinton, and George Boettner, Lab Manager in the Dept. of Environmental Conservation at UMass Amherst.

What is Winter Moth?

All deciduous trees are at risk. Research shows that 4 consecutive years of defoliation can lead to tree mortality.

Where is it from?

Initially, the hardest hit areas were in Eastern Massachusetts, especially southeastern MA, including Cape Cod. Winter moth was initially introduced to North America from Europe in Nova Scotia sometime prior to 1950.

Susceptible Plants

Oaks, maples, cherries, basswood, ash, white elm, crabapples, apple, blueberry, and certain spruces such as Sitka spruce.

Young larvae (caterpillars) wriggle into buds of apple, blueberry, cherry, crabapple, maples, oaks etc., in the early spring just before or at bud break. Once inside the buds, the tiny caterpillars begin feeding. Delayed bud opening due to cool weather can lead to bud death. Larvae move from bud to bud as they feed. As the larvae grow, they feed in expanding leaf clusters and are capable of creating defoliation in high populations.

Life Cycle of Winter Moth

Each moth lays 100 -200 eggs and the average infested tree has up to 150,000 leaf defoliating caterpillars.

Moths, the adult stage of Winter Moth, emerge from the soil usually in late November and may be active into January whenever the air temperatures are mild. The male moths are light brown to tan in color and all four wings are fringed with small elongate scales. The male moths are strongly attracted to lights and can often be found flying around outside lamps or in car headlights.

The female is gray, almost wingless (brachypterous) and, therefore, cannot fly. She emits a sex pheromone that often attracts clouds of male moths. Females are usually found at the base of trees or scurrying up tree trunks, but can be found almost anywhere. After mating, the female deposits a loose egg cluster in bark crevices, under bark scales, under lichen, or elsewhere. The adult moth’s then die and the eggs over-winter.

Egg hatch occurs in the spring just at or right before bud break of most of the host plants. Some of the newly hatched larvae crawl up tree trunks and produce a silken strand of silk, which makes them air buoyant. This “ballooning” along with wind patterns means that winter moth caterpillars can arrive in areas where they have not been expected.


Well, at least it’s something seasonal. Having reported on butterflies, bees, warblers and unseasonal flowers in recent days Winter Moths attracted to the lounge window last night were a reminder that it is, after all, still only January!

Winter Moths may give moths a bad name because of their bland appearance but, as is so often the case with insects, they have a fascinating life-cycle.

Surprisingly, the adult females are flightless. Being wingless they crawl up the trunks of trees, give off pheromones and lie back and await a male!

Once mated they will lay their eggs in developing buds before dying shortly afterwards.

In the spring the caterpillars time their emergence with that of developing buds in April and will feast on a variety of tree foliage. The caterpillars spin threads around the leaves and feed amongst it.

They have also been recorded hanging from a spun silk thread and being blown by the wind on to another branch or tree, a method of distribution known as ballooning.

The caterpillars shown below were found last April feasting on apple trees growing amongst hedgerows along the South West Coast Path near the Helford River, Cornwall.

Need help with what to do in your garden?

Q What are winter moths?

A Winter moths are a group of pests that include the most damaging caterpillar, the winter moth itself (Operophtera brumata), the northern winter moth (Operophtera fagata), the mottled umber moth (Erannis defoliaria) and the March moth (Alsophila aescularia).

Caption: Fix grease bands to the tree in October to trap the female moths

Q Which trees do winter-moth caterpillars feed on?

A Although considered a pest of apples, they also eat pears, plums and cherries. The northern winter moth usually turns up only where birch trees grow near an orchard.

Q How do I recognise winter-moth caterpillars?

A Winter moth caterpillars are green with black heads and yellow stripes along their back and sides. Fully grown, they are 25mm long. The Northern winter moth caterpillars are the same, except that the stripes are darker. The March moth caterpillar is yellow/green with fine, dark green and yellow stripes, and yellow lines along the sides. It is similar in size to the winter moth, but thinner. Mottled umber caterpillars are bigger, reddish brown with yellow sides and a dark, wavy stripe.

Q How do I know if winter moths are about?

A You’re unlikely to notice the moths, but the caterpillars have a distinctive looping walk. The winter and March moth caterpillars spin a little shelter joining two leaves or a leaf and a bud. The first sign that they’re attacking your trees is likely to be leaf damage, by which time the caterpillars are long gone. They feed on young leaves as they expand, leaving irregular holes, and strip large quantities of foliage. The tree won’t die, but it won’t produce a crop that year, and you will only have a small crop the following year.

The caterpillars may also attack flower buds and young fruitlets. This is likely if the leaves have not opened when the caterpillars emerge from the eggs. When fruitlets are attacked they may fall early. If they survive, the surface heals leaving a corky, sunken scar. When the caterpillars nibble deeper, there is a navel-like depression in mature fruit. The fruit is edible, despite these marks.

Caterpillars of the mottled umber moth are not so damaging, as they seldom feed on fruitlets or flowers. They don’t spin shelters of leaves so are easy to recognise.

Q How serious is the damage winter moths cause?

A The overall effect of these moths on a healthy tree is usually small, and they have many natural predators. Neither overall growth nor cropping should suffer greatly, so you only need to take action when it looks as if the damage is going to be severe.

Q How can I tell that winter-moth damage is going to be severe?

A As soon as the buds show signs of growth, look for the tiny winter moth caterpillars on the fruit spurs and leaf buds. If you see ones with a looping gait, be ready to take action. In cold weather they may shelter inside buds, so break a few open to check for caterpillars.

Q Can you tell me more about winter moths?

A Female winter moths emerge between October and April and crawl up the trunk to lay their eggs. They have no wings and look more like a beetle or a spider. The male is the little moth often seen in car headlights in the winter. The winter moth lays 100-200 orange eggs in bands or clusters on the twigs or buds. They usually hatch when the buds break; the caterpillars feed on shoots and then drop to the ground to pupate. The female moths cannot fly, but the tiny caterpillars parachute using silk threads and are carried by the breeze to other trees. The male March moth is grey-brown with a 32mm wingspan. The female is drab and wingless. The eggs are laid on twigs and have a hairy covering. Mottled umber moth males have a 42mm wingspan and are brown-yellow with darker mottling and banding on the wings. They fly mainly from October to December, with a few turning up until February. The female is, again, drab and wingless.

Q How do I control winter moths?

A The caterpillars can be picked off by hand, but it’s more effective to catch the female moths, which can be trapped by fitting grease bands round the trunk. You’ll need to reapply grease regularly, and keep the bands free of debris. Fix them about 0.5m off the ground in October and remove them in late spring. Where posts or ties allow the insects to bypass the grease, put one above the tie. The greasy zone should be 12-15cm wide. Don’t use car grease directly on the trunk – mineral oils are damaging. Use grease sold for the purpose, as this can be applied directly on to the bark.

Q Is it worth spraying winter moths?

A Rarely – but if it’s really bad, treat with an insecticide approved for caterpillar control on fruit following the information on the packet for which trees they can be used on and how often you need to spray.



Male and female winter moths emerge from the soil in their adult form (as moths) from early November and through to mid January in warmer winters. The female pests cannot fly and immediately make their way to the nearest tree trunk of suitable tree varieties. It is thought that the females recognise tree trunks because of their profile in low light. They then crawl up the tree trunk into branches. Along the way they mate with male winter moths which can fly very well.

Eggs are laid in the crevices of the bark on the trunk and branches. The eggs are light green at first and laid in clusters of 30 or so. The adult moths have then completed their useful life so die. As the larvae grow in the egg case they turn orange at first and finally very dark brown / blue just before hatching.

One of the key factors which determines when the eggs will hatch is temperature – a week or so with temperatures around 13°C / 56°F is just right for them. Unfortunately this almost always coincides with the period when affected trees and shrubs in your garden are beginning to produce flower and leaf buds. The tiny caterpillars then search out the forming buds and “worm” their way into the outer scales and begin eating their way inwards.

To increase their chances of finding tasty buds and also to enable them to spread to nearby trees some of the caterpillars will spin a thin thread and hang downwards from the thread. Some will latch onto buds lower down the tree but others will be blown away in strong winds and hopefully land on another tree and then attack that.

Winter Moth Caterpillar hanging by a thread

The above picture (courtesy of one of our readers, Tony R) shows this stage of their life cycle.

The caterpillar will eat the interior of a bud, destroying it completely. They then move onto other buds and developing leaves. Many of the leaves will end up with holes in them.

The above picture shows a fully developed Winter Moth caterpillar and is very typical of how they look as they move with an arched back to almost push themselves along. At their longest they are about 2.5cm / 1in long. In early to mid June they drop to the ground and pupate, emerging as adult moths in November.


Well established and healthy trees are very often quite capable of growing through the damage caused by winter moths, producing a reasonable amount of apple / pear / plum or cherry fruits. Just because the moths have attacked the tree one year does not mean they will be attacked the next year. So in many cases it is possible just to ignore the damage.

For some trees however, especially younger trees and those not in the best of health, the damage can be severe, even fatal.

There are two stages in the life cycle of Winter moths when they are vulnerable. The first occurs when they emerge in November and the females attempt to climb up the tree. Almost all garden centres and also online suppliers sell grease bands which can be wrapped around the lower part of the tree trunk in early to mid October. These are very sticky and the females get suck on them and die. Probably the best form of this barrier is a glue one which is painted on the trunk in place of the bands. Both must be kept sticky from late October through to late March.

One word of advice if your trees are staked. To the eyes of a moth, a tree trunk and a tree stake look much the same and they will crawl up both often crossing from one to the other. Grease bands and / or glue therefore need to be applied to the tree stakes as well as the trunks for best control.

In conjunction with this, attracting birds will greatly help. Tits especially love to eat these bugs and encouraging them into your garden with the correct bird food will reduce the moth numbers significantly.

The second stage of their development which makes them vulnerable is when the eggs hatch in late March to late April. At this stage the tree can be sprayed with a pesticide that will kill the caterpillars, many will also kill aphids as an added bonus. Read the labels carefully and follow the instructions in detail. Spraying when the tree has blossom on it is not a good idea because this may well kill pollinating insects – so read the instructions on the pack carefully. Pesticides which contain deltramethrin or pyrethrum are currently the ones to look for.

One other general approach which will reduce numbers is to cover around the base of the tree with a layer of black plastic. This will have two effects, firstly it will prevent the caterpillars from hiding in the ground when they drop to the floor and secondly it will prevent many of them emerging successfully in November.

Preventing Winter Moth Damage

Are your crabapple and maple trees looking like Swiss cheese? Tiny green winter moth caterpillars are the likely culprit.

Winter moth caterpillars feed on a wide variety of plants, but their favorites include maples (including Japanese maples), oaks, blueberries, apples, linden, ash, and horse chestnut. They also feed on roses and some perennials. If you have had damage on trees in recent years, it’s important to treat early to prevent weakening the trees. Another benefit of early treatment is that eggs can be treated with dormant oil spray, which is a less-toxic alternative to some of the insecticides used to treat caterpillars once they have hatched. Treatment can begin as soon as the temperature is above 45 degrees, and likely to stay above freezing for a couple of days.

Winter moth damage usually starts while buds are still closed, in late March-mid April. This time is particularly critical for blueberries and other fruit trees, because damaged flower buds mean no fruit. When leaves emerge, the caterpillars continue feeding, and damage to leaves continues through May. By late May, when most people notice that their maple leaves are full of holes, it is too late to treat the caterpillars, which are on their way to becoming adult moths.

If you are noticing damage in late spring, put a note in your calendar to seek treatment early next spring, before the next generation of eggs hatches out.

Winter Moths

Winter moth caterpillar © Milan Zubrik, Forest Research Institute, Slovakia, Bugwood.org

The winter moth (Operophtera brumata) is an invasive insect that can wreak havoc on our trees. Introduced into the United States from Europe via Canada, is most commonly observed in late fall, early winter as a whitish adult moth and in spring as a tiny green caterpillar.

Life Cycle

winter moth © Robert Childs, University of Massachusetts, Bugwood.org

The adult winter moths emerge from the ground in November or December, but only the male is able to fly. The female climbs to the base of a tree or building and attracts the male through the pheromone (sex scent) that she exudes.

After mating the female lays a cluster of approximately 150 eggs under tree bark or in tree crevices, and her life is now over.

In March or April the eggs hatch into a smooth green inchworm with a narrow white-stripe running lengthwise on each side of the body. The caterpillar spins a strand of silk, which, with the help of air currents, takes it into tree canopies in a dispersal method known as “ballooning.”

Once there, the damage to the tree begins as the caterpillars work their way into the tree buds and leaves to feed. Winter moth caterpillars can also drop from trees to nearby ornamental shrubs such as roses. When feeding ends in mid-June the caterpillars migrate into the soil to pupate and emerge as moths.

Situations & Solutions

The most visible effect of the winter moth infestation is defoliation of trees and shrubs in spring. In Massachusetts, winter moths affect maple, oak, and ash as well as fruit producers such as apple, crabapple, and blueberry. Newly-hatched caterpillars burrow into the buds of trees and shrubs before they open, and begin to feed; when they finish with one bud they move to another.

The most heavily infested trees may be completely defoliated, and while healthy trees are capable of putting out a second set of leaves, the process puts severe stress on the tree. Research has shown that complete defoliation can reduce the annual growth rate of some oak species by as much as 47%, and successive defoliations can kill branches or entire trees.

The impact of the caterpillars may also be exacerbated by secondary effects such as prolonged, cool springs, which allow the caterpillars to feed longer in the buds; dry years which put trees under additional stress; and infestations of other insects such as bark beetles, fungal parasites, or other moth species.

Controlling Winter Moths

In 2005 and 2006, in a cooperative effort by the Department of Entomology at the University of Massachusetts and the Forest Health Program at the Massachusetts Department of Conservation and Recreation, hundreds of parasitic flies known as Cyzenis albicans were released at Wompatuck State Park in Hingham and on town-owned property in Wenham, MA. In 2011, the university shared an update on the project. Cyzenis albicans has been effective in combating winter moth populations in Nova Scotia, as well as other parts of Canada.

The fly lays its eggs on the leaves eaten by winter moth caterpillars during the spring. When the eggs are consumed, along with leaves, the eggs hatch inside the caterpillar and the larvae consume the caterpillar from within, eventually causing the moth to die. The fly pupates inside the carcass of the caterpillar and, the following spring, emerges as an adult fly to mate and begin the cycle again.

Homeowners concerned about damage to trees and shrubs should check susceptible plants for the little green “inchworm” caterpillars in early to mid-April. If a serious infestation is apparent, there are a few steps that can be taken to minimize damage.

Supplemental watering. Providing extra water throughout the season will help trees recover from the stress of defoliation and re-foliation,

Tree banding. Paper or plastic strips covered with a sticky substance are commercially available to create a barrier that entraps the adult females and caterpillars. Though logical, this method has not proven to be effective for major infestations because:

  • The sticky bands fill up and lose their effectiveness rapidly
  • Some insects are able to pass under the bands
  • Female moths confronted with the band will lay their eggs below it.

Nevertheless, it may be worth a try for minor infestations on individual specimen trees.

Oil sprays Available at garden stores, these sprays are applied to tree trunks and branches to kill eggs before they hatch. This treatment also gives imperfect results, but has been recommended for fruit orchards, where flower bud damage can be devastating to crops.

B.t. kurtstaki (Bacillus thuringiensis kurtstaki) This bacterial pesticide has proven effective in killing young caterpillars of a number of pest species. Unfortunately, it can also kill many of our native butterflies and moths, the vast majority of which are either harmless or beneficial. For B.t. to be effective, it must be applied to the surface of the leaves once they have expanded for the caterpillars to ingest it, i.e. after much damage has already been done within the leaf buds. Also the mature caterpillars feeding on expanded leaves may be resistant to the bacillus.

Rhode Island Apple IPM

When winter moth eggs hatch depends on temperature and other factors. I don’t expect eggs to hatch until after red maples start blooming and when McIntosh apple buds begin to crack open and expose a little bit of green tissue.

Winter moth eggs tend to hatch at McIntosh apple ‘green tip’ and red maple tree bloom.

Tree wraps have been set up to monitor eggs in 14 locations in RI, one in CT and by at least two Massachusetts blueberry growers. Tree wraps encouraged female winter moths to deposit eggs below tree wraps back in November and December. Tree wraps have been removed and we found hundreds of eggs to monitor. Winter moth eggs are orange now, but turn blue a couple of days before hatching. Very handy for monitoring egg hatch! I’m asking egg monitors to start watching their eggs March 20th.

Tree wrap and close up winter moth eggs. Eggs are nearly impossible to see without setting up tree wrap in the fall.

For landscape trees it’s not important to control winter moth when eggs start hatching, but for apple, pear, and blueberry growers it’s very important. Once eggs hatch, winter moth caterpillars wriggle into swollen buds and begin feeding. For apple & pear trees and blueberry bushes, swollen buds are primarily flower buds. Caterpillars crawl inside flower buds and begin feeding. Once caterpillars are inside buds they are protected from insecticide sprays until close to bloom and by this time many flowers may have been damaged or destroyed, destroying the crop. Landscape trees, on the other hand, can withstand early winter moth feeding damage. To save landscape trees from being defoliated, insecticides can be applied after trees leaf-out, but while caterpillars are still small and before excessive feeding damage has occurred.

Dormant oil can be applied before eggs hatch, but this may not be very effective if unsprayed trees are nearby or if you cannot get complete coverage with an oil spray. Winter moth eggs are often located in bark nooks and crannies, so complete oil coverage is very difficult. When applying oil, temperature must be above freezing and remain above freezing for 24 hours after application or plant damage can occur.

Winter moth caterpillars are pretty easy to kill, provided they are not inside closed buds. Insecticide choices for when caterpillars start to hatch for fruit growers include, but are not limited to, spinosad, Imidan, Sevin, Malathion and synthetic pyrethroids such as Asana. Spinosad product names are Delegate (for commercial growers), Entrust (for organic growers), and Captain Jack’s Deadbug Brew (for backyard growers). Adding a dormant oil may be useful for the first spray of any of the listed insecticides.

Once buds open, B.t. kurstaki products (Bacillus thuringiensis kurstaki) such as DiPel and Biobit work well. For landscape trees, winter moth caterpillars can be controlled once trees leaf out with spinosad (Conserve), B.t. kurstaki (Dipel Pro, Javelin, and others), as well as synthetic pyrethroids such as bifenthrin. B.t. products are a good choice because they kill only caterpillars, but B.t. products break down in sunlight after 3-5 days so may need to be reapplied more frequently.

There is a lot of interest in gypsy moths this year, but gypsy moth eggs won’t hatch until late April or early May. This time of year gypsy moth egg masses can be found and scraped off trees. This may be beneficial in some situations, but not many.

Gypsy moth egg masses can be scraped off now before they hatch.
Egg masses are weathered and harder to see now than they were last summer.

Heather Faubert
URI Cooperative Extension

How to Avoid Another Devastating Year of Winter Moth Infestation

The winter moth (Operophtera brumata, of the insect order Lepidoptera—moths and butterflies—and the family Geometridae for the bug geeks) is an invasive species that is now a major problem in Massachusetts. Infestation is expected to be even worse this year than in previous ones. Some of the more common trees that the winter moth targets are maple, oak, ash, birch, beech, apple, cherry, pear and rose.
Most people notice winter moths around Thanksgiving (late Nov. to early Dec.) when adult moths emerge and the males begin to fly. At this point in their life cycle, there is no effective treatment for the moths, but they don’t do any damage at this time either, because they’re not feeding. At this stage, the male moths are able to fly; the female moths are flightless because, although both sexes have wings, the females’ wings are very small and therefore ineffective for flight.
Female winter moths have to climb the side of the host tree to lay their eggs on the trunk and branches. After the eggs are laid, the adults die and the eggs remain on the stem of the tree throughout the winter and into spring.
The caterpillars begin to emerge from late March to early April, and this is when the attack begins. After the winter moths emerge from the eggs, they spin a silk thread and drop down from the tree and are carried by the wind to a feeding spot, in a process known as ballooning. At this early point in their life the leaves have yet to emerge so they will squeeze their way into a bud on the tree and begin feeding on the swollen bud. As the plant continues to grow, the caterpillar grows as well and continues to eat the plant’s leaves until the end of May to the beginning of June.
Obviously, this is the time period when the insect does the most damage to your plants. In many cases, all of the leaves are destroyed, leaving the trees completely defoliated, which is obviously very detrimental to the trees’ long-term health. Many healthy, well-rooted trees can withstand being defoliated; while the trees have enough reserve nutrients to push out new leaves, they have enough reserve for only one year. If the defoliation occurs year after year, the tree will eventually be unable to recover. After a few years of this level of stress on the tree, it will start to show signs of dieback throughout the canopy, such as, a loss of leaves or a thin canopy, and eventually it will die.
It is during this time in the moths’ life cycle that control and treatment are most effective. One of the best methods of treatment is with a Spinosad product that works by attacking the nervous system of the winter moth. Treatment is effective if the moth has direct contact with the chemical or it feeds on treated foliage.
If left untreated, winter moths will continue to eat until fully grown, into the beginning of June. Once they are done feeding, they will drop down from the tree into the soil and immediately spin a cocoon and pupate. When they are in their pupate stage there is no control, except for a few natural predators. This is where they will stay for most of their life cycle. They do not emerge from the soil until around Thanksgiving, when the cycle of devastation begins again.
For more information or to have your trees sprayed to prevent winter moth damage, contact a local licensed arborist.
Written by Ryan Anzivino, Certified Arborist # NE-6914A, of Bellingham-based, family-owned Outdoor Maintenance Co. Office tel: (508) 883-3564; cell: 508-498-4397.

Operophtera brumata

pdf version


Winter moth was introduced into North America from Europe. It was first recorded in Nova Scotia in the 1930s and then in the Pacific Northwest (British Columbia, Oregon and Washington) in the 1970’s. Winter moth showed up in eastern Massachusetts in the early 2000’s and has since spread westward in MA, into Rhode Island and now coastal Maine from Kittery to Bar Harbor.

The larvae of winter moth defoliate deciduous trees and shrubs in early spring. Trees heavily defoliated by winter moth for three or more years can exhibit branch dieback and mortality.

At least some of the winter moths were likely introduced into Maine as cocoons in the soil of landscape trees and plants from infested areas in southern New England.

This insect is very closely related to the native Bruce spanworm, Operophtera bruceata. It is extremely difficult, (and impossible in the field), to tell the two species apart. Bruce spanworm is an occasional pest of trees in Maine and rarely remains a problem for long. This is in contrast to winter moth that has no natural enemies in North America to keep the populations in check.


Winter moth feed on the leaves of many deciduous trees and shrubs in Maine. Preferred hosts include oak, maple, apple, elm, ash, crabapple, cherry, and blueberry. The larvae will feed on many other plants as well.

Life Cycle and Description

The larvae hatch in early spring from eggs laid on the trunks of host trees. They crawl up the trees and burrow into both leaf and flower buds, feeding on the expanding buds and foliage. The larvae also produce silk that they use to “balloon” to new locations. They also use the silk to tie buds and leaves together when they are young. Winter moth larvae are light green to brownish-green inchworms with longitudinal white stripes on each side of the body and are ½” long when full-grown.

Mature larvae spin down out of the trees to pupate in the soil, not only under the trees, but also in the surrounding area. The larvae form earthen cocoons where they stay from June to November. They are well protected during this time and are not affected by pesticides.

Adults are active from late November to January whenever the temperature is above freezing. Males are small, light brown to tan moths. They are attracted to lights and a pheromone released by the females. Female adults are small, gray, with reduced wings and flightless. They are most commonly found crawling at the base of trees. After mating, females deposit their eggs in host tree bark crevices, scales, or loose lichen. The eggs over-winter and hatch in the spring when temperatures reach ~55° F.

Above: adult male (left) and female (right) winter moths, Operophtera brumata (Photos: Bo Zamba (L), P. Johnson)


An early April horticultural oil spray on trunks and branches of infested trees to kill eggs may be helpful. However, some eggs are protected under bark flaps and lichens.

Some products are available to act as a barrier to climbing adults. Generally, heavy weight paper strips that are covered with a sticky substance are put on the tree to snare the climbing moth or caterpillar. This should be done in November when the adults are active.

Research is being done at the University of Massachusetts in Amherst on a parasitic fly (Cyzenis albicans) that has been effective in controlling winter moth in Canada and the Pacific Northwest. This is a long term biocontrol option but it will take years for it to become effective after releases are begun.

DO NOT MOVE LANDSCAPE MATERIAL from infested areas as the cocoons of winter moth are in the soil from June through November.

*Note: These recommendations are not a substitute for pesticide labeling. Read the label before applying any pesticide. Pesticide recommendations are contingent on continued EPA and Maine Board of Pesticide Control registration and are subject to change.


For your own protection and that of the environment, apply the pesticide only in strict accordance with label directions and precautions.

Maine Forest Service – Forest Health and Monitoring Division
January 2013


By Faye

Winter moth (Operophtera brumata) originated in Europe, and came to BC in the 1970s. The larvae, smooth green ‘inchworms’ about ¾” long, hatch in spring and can cause serious damage to emerging leaves if not controlled; after three years of infestation the tree can become so weakened that dieback and possible mortality can occur.

Their favourite hosts include oak, apple, crabapple, ash, birch, maple, and other broadleaf trees. Damage from winter moth has been extensive this year, with blueberries and roses also falling prey to their voracious appetites.

The following excerpt from Linda Gilkeson’s website explains the most effective means of control, and the time is right now to get this done.

Tree Bands: If winter moth caterpillars ate holes in your tree leaves early last spring (apples and other fruit, oaks, other deciduous trees), then mid-October is good timing to put up sticky tree bands to intercept the females before they lay eggs. The female moths can’t fly so when they emerge from their cocoons at the base of trees they have to walk up the trunk to lay eggs out on the branches. Spread insect glues – ‘Tanglefoot’, ‘Tangletrap’ (‘Tree Guard Tape’ is a ready to use – double sided sticky tape) available at garden centres on a foot-wide band around tree trunks. The band can be anything that is easy to wrap around the trunk: plastic food wrap, waterproof package tape, or other waterproof material that can be spread with glue. If the tree has deep crevices in the bark, wrap a layer of cotton batting around the tree first, pushing it into the cracks to block moths from crawling under the sticky band. Don’t put the glue directly on bark—it will damage young bark and will also keep on catching insects—mainly beneficial ones–during the growing season (and also kid’s hair, dog’s tails, shirt sleeves, etc.). The moths lay eggs from late October to January so you can remove the tree bands in February.

There is a more extensive section on Winter Moth in Linda’s book Natural Insect, Weed and Disease Control. She mentions removing and replacing the bands when they become full of trapped moths, and making sure that each trunk of a multi-trunked tree is banded. On a lighter note, she advises placing the bands high enough to avoid the aforementioned small children’s hair or dogs’ tails!
Some further options mentioned are:

*** Spray dormant oil between December and February, which smothers the eggs. This must be done before buds begin to swell.

***Spray BTK (Bacillus thuringiensis kurstaki) in the spring, when caterpillars are small and actively feeding, but make sure to get the spray into new buds and rolled leaves.

***More of a prevention than a cure, planting to attract beneficial insects, beetles, ants and birds which will eat the cocoons left on the ground. (planting chart p. 108 in the book)

As always, we thank Linda Gilkeson, PhD entomologist for her help and advice regarding these pesky varmints!

Wildlife & Nature

Gypsy moth caterpillars defoliated about 43,000 acres of Rhode Island forest last year, thanks to a dry May that aided their survival. In years when it’s rainy in May, the moisture abets several diseases that get passed back and forth between gypsy moth caterpillars, causing the population to crash. So Faubert has her fingers crossed that Rhode Island will experience a wet May.

Homeowners seeking to protect their trees from winter moth defoliation should take action immediately. Faubert said it’s best to spray insecticide on trees while the winter moth caterpillars are still small.

“Waiting until the trees are halfway defoliated won’t really do much good,” she said.

According to DEM, the recommended treatment against the caterpillars is a pesticide containing the relatively safe bacterium Bacillus thuringiensis or Bt. Caterpillars die when they consume leaves sprayed with the pesticide, which is most effective before the caterpillars are full grown.

“That’s the safest thing to do,” Faubert said. “The problem is that the spray only lasts from three to five days before it breaks down. So if you have a prized tree you’re trying to save and there are untreated trees nearby, caterpillars may get blown onto your tree after the pesticide is no longer effective. So one shot of insecticide may not do the job.”

Physical barriers such as sticky tape or grease applied to the base of trees isn’t considered effective at stopping winter moths.

One strategy that Faubert has experimented with is biological control. Researchers have identified a parasitic fly that is known to control the spread of winter moths in their native Europe. The fly lays its tiny eggs on tree leaves, and when the caterpillar consumes the eggs while eating the leaves, the eggs hatch inside the caterpillar and eat the caterpillar from the inside out.

Faubert released groups of the parasitic flies in seven locations in Rhode Island between 2011 and 2014. But, she said, “if it’s going to work, it takes years.”

In the meantime, she advises residents concerned about their trees to contact a local landscaper or arborist who can assess and treat their trees. The Rhode Island Nursery and Landscape Association has a list of those who can do the job.

Rhode Island resident and author Todd McLeish runs a wildlife blog.

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