|
Eggs:(see
Fig_13 & 18.jpg): Male and female winter moths
emerge over a period of several weeks beginning in late November
and continue through December. During this time period, the
moths mate and the females lay eggs. Female winter moths lay
their eggs primarily on the trunks and branches of their host
plants. The tiny oval eggs first appear in late November and
continue to appear through December as new female moths appear.
Initially, these eggs are tiny and green in color. They will
be scattered loosely along the bark, in bark furrows, under
lichen, and out on the larger branches. After a short time
period, the eggs turn a pinkish-orange color and thus are more
visible (see Fig_1). Within days prior to
hatching in the early spring, winter moth eggs will turn very
dark in color.
Treatment
for the Eggs: Given that many winter moth eggs are
exposed on the bark, the potential to manage them with a horticultural
oil spray exists. Typically, dormant oil sprays are applied
in the very late winter or very early spring depending on temperatures
and host plant phenology. Oil sprays can be applied in the
fall 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.
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 creating
injury to the plant (phytotoxicity). Any weather conditions,
such as cool and cloudy, can also delay drying time and enhance
the potential for injury. Oils work by suffocation and can
be affective on the eggs. Oils must cover the target organism
at the time of application or no Insecticidal effects will
result. Eggs that are protectively hidden within crevices and
under lichen will not be covered by the spray nor killed. Given
the phenomenal numbers of winter moth eggs in Massachusetts
this year, oil sprays will most likely only achieve limited
results; eggs are virtually everywhere on trees and shrubs
and new caterpillars will quickly migrate from untreated areas
to the oil-treated plants. Commercial spray applicators sometimes
add a chemical companion, such as a specific organophosphate or carbamate, or pyrethroid,
in with the oil spray, according to label instructions. 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. Mixing compounds that should not be together
can cause serious injury to plants, the environment and the
applicator. The theory of mixing a specific insecticide with
the oil spray is to kill any newly hatching caterpillars that
were not affected by the oil alone while still in the egg stage.
Newly
Hatched Caterpillars (see Fig_5): Winter moth is a
generalist feeder and has the potential for a rather wide host
plant range. In general, however, winter moth caterpillars
commonly feed upon all maples, oak, apple, crabapple, ash,
fringetree and blueberry, This pest has been known to drop
from trees and feed on perennials such as roses and others.
It has not been commonly seen feeding on magnolia
and flowering or kousa dogwoods. There is evidence, although
not yet well documented, that winter moth caterpillars time
their hatching from the egg closely to the time of bud-swell
of the specific host plant that the eggs are on. This suspected
phenomenon only occurs in larger stands that consist primarily
of one type of tree (e.g. oaks or maple). It has not been observed
in landscapes with mixed tree species. It is estimated that
winter moth eggs hatch between 20-50 Growing Degree Days (base
50) in Massachusetts. Typically, this can occur anytime late
March (during atypically warm springs) into the second or third
week in April (cool springs). The tiny (less than 1 mm) caterpillars
then spin a small silk strand and become air-buoyant and are
carried upwards on air currents into the tree canopy where
they then try to “weasel” between the bud scales,
bracts, etc. to get into the buds. They do not chew their way
in via an entrance hole. If buds are not yet swollen enough
for them to gain access, these small larvae will then spin
down from the tree on a silken thread and be carried away by
the wind, which is a dispersal process known as ballooning.
This is the
stage where high levels of injury to the host plant can occur.
The longer that the buds stay swollen but unopened, there is
a greater potential for feeding injury. Winter moths will enter
both leaf and flower buds. For blueberry growers, this is the
most critical stage of winter moth activity. If flower buds sustain
heavy feeding, there will be no flowers and thus no fruit. There
are no known controls for winter moth in this life stage.
Free-Feeding
Caterpillars (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. Winter moth will be in this stage until
late May or early June whereupon they drop to the soil and
almost immediately spin a cocoon and pupate. While still on
the host plant, however, they are exposed and very treatable
with a variety of products.
1. 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 pollute 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 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 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).
|
2. Spinosad
Products: The first version of this product in the
USA was only available to commercial licensed pesticide applicators
and was trademarked as Conserve SC™ (Dow AgroScience);
other trade named products are now available for specific
uses. Since 2004, homeowner spinosad products have become
available and two common ones are known as Monterey Garden
Insect Spray™ and
Bull’s-Eye Bioinsecticide™. These products are
derived from a bacterium that is subjected to a specific
fermentation process to derive 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
products work well on caterpillars of all ages, even
caterpillars known as sawfly caterpillars, which are
the larval stage of certain wasps in the order, Hymenoptera.
|
B. Although
fairly safe by not harming parasites and predators,
the label does warn that it 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.
|
3. Tebufenozide (e.g.
Confirm T&O™, Dow Agro Sciences): This product is
only available to licensed commercial applicators and not homeowners.
Its mode of action (how it kills) is that of an IGR (insect
growth regulator). Tebufenozide mimics 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. It 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.
4.
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, the more conservative choices now are the pyrethroids.
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,
often 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.).
4.
Physical Barriers: For years, sticky products have
been available for wrapping around tree trunks to (ostensibly,
at least) prevent such pests as gypsy moth, fall cankerworm
and winter moth caterpillars, as well as the wingless adult
females, from climbing up trees. Initially, the product consisted
of a band that was wrapped or placed around the trunk of
a tree and then coated with a Tanglefoot™-type product,
which is remarkably sticky. In small infestations and with
limited trees to protect, this may or may not be beneficial
overall; the research is still not quite complete. Newer
products now consist of a fiber-batting band (about one inch
thick) that wraps around the tree trunk. A plastic, doublewide
band that is only sticky on one side is placed sticky-side
inward around the batting, and being double-wide, half of
it hangs down below the batting and held out away from the
tree (see Fig_18) As wingless female moths
race up the trunks and encounter the bands, they attempt
to climb over the bands and become stuck on the sticky plastic
band. The current infestation in Massachusetts is so large
(outbreak proportion) that females and attracted males both
become stuck to the band and saturate it within hours. Newly
arriving females can then walk over the bodies of the stuck
ones and gain access to the rest of the tree. These bands
are also marketed to prevent caterpillars from climbing up
trees in the spring. However, caterpillars, due to their
ability to balloon, can blow from one treetop into another
thus by-passing the trunk bands. These bands are not recommended
as a management tool when population numbers are high. (see
Fig_19).
Winter
Moth Pupae in the soil: There are virtually no controls
for this pest in this life stage other than natural predation
but such factors as ground beetles.
Adult
Winter Moths: Male winter moths (see Fig_13) have
wings and are rather drab-colored moths. The hind edge of their
wings is fringed with small hairs and the bottom row of dark
banding near the tip of the wing appears as a series of hash
marks. This becomes important when trying to separate them
from male fall cankerworm moths (see Fig_15),
which are active at the same time. The male Fall Cankerworm
is similar to winter moth males but has a distinctive light
colored patch near the distal end of the front wing on the
leading edge.
Adult female
winter moths (see Fig_20)) are said to be wingless
but they actually have greatly reduced wings (brachypterous)
and are smaller than the totally wingless (apterous) adult female
Fall Cankerworm moths (see Fig_20).
Males and
female moths of both species emerge around Thanksgiving time
and may continue to emerge well through December whenever milder
temperatures prevail during that time period. The moths of both
species are attracted to lights. Females of both species will
orient on a vertical silhouette, such as a tree trunk, and race
up it while emitting a sex pheromone to attract males of her
species. Clouds of male winter moths can be seen flying around
tree trunks, resting on the bark and mating with females at this
time (see Fig_16 & 17). Once mated, the
female may continue scurrying up the tree and begins to lay eggs.
Both males and females die soon after mating and egg deposition.
Each female winter moth lays up to 150 eggs. See the first paragraph
for more on winter moth eggs. Fall Cankerworm females lay their
eggs around the small stems of host plants. These egg clusters
look like tiny individual barrels that are tightly packed together.
There are no control options for the adult stages of these moths.
They do not feed in this life stage. |
