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University
of Rhode Island GreenShare Factsheets
Cutworms
on Turf Agrotis
ipsilon (Hufnagel)
Lepidoptera: Noctuidae
Cutworms can
be destructive insects, particularly on golf courses and other highly
maintained turf areas. Damage can occur any time from late May through
the rest of the growing season. Damage is usually most obvious in
June through August, when temperatures are highest and cool season
grasses are not growing vigorously. Damaged spots look like unrepaired
ball marks and can persist for several days.
There are several species of cutworms which attack turfgrasses in
New England. The adults are dull colored moths with a wingspan of
one to two inches. The front wings have distinct scale patterns
(faint lines, circles and kidney-shaped spots) which can be used
to identify species. The
black cutworm, which is the most common species in most of New England,
has a band of dark brown scales in the midsection of the front wing
and has a dagger shaped marking on the outer edge of a kidney shaped
spot.
The caterpillars (the stage that actually damages turfgrass) reach
50 mm (2 inches) in length. Most species have a background color
of dull gray or brown but usually have some stripes of brighter
or sometimes darker colors. Black cutworms are normally dark gray
or nearly black but may have a hint of green in the stripes. The
lower half of the body is slightly lighter in color. Each cutworm species
has its own life cycle, but most species which occur in New
England cannot survive the local winters. Adults migrate
south (to Maryland or the Carolinas) in the autumn and return on
weather fronts in the spring. When the adults return, they
begin
to lay eggs on the tips of grass blades. Tiny caterpillars only
1 mm (1/32 inch) long hatch and begin to feed on the foliage.
Caterpillars
go through six or seven molts during their development. As they
grow, they gradually move deeper into the thatch, carving "burrows" which
they line with green excrement. Some large caterpillars stick
their heads out of their burrows at night, chop off grass plants
which are within reach and pull the blades back into the burrow
for subsequent feeding. After feeding for two to four weeks,
the
caterpillars transform in the soil to pupae (cocoons), which are
relatively smooth, torpedo-shaped and brown. In
some parts of the country the black cutworm may complete as many
as six generations per year. In New England the population
appears
to complete two or three generations in a "normal" year, but there
is considerable overlap so that a turf manager may be able to find
any stage (adult, egg, caterpillar or pupa) at any time during
the
growing season. Cutworms feed on
several kinds of grasses. They seem to be most apparent in
turf areas maintained at very low mowing heights. Cutworm
damage on turf looks like small pock marks (or ball marks on a
putting green). Closer examination reveals a small burrow and
several grass
plants around the perimeter of the burrow which have been sheared
off near ground level. Often these burrows are lined with green,
pellet-like matter. This is caterpillar "frass," or excrement. Cutworm
moths and caterpillars are nocturnal (active at night), so normal
daytime inspections will not unveil the insects. The easiest way
to determine whether cutworm caterpillars are present in a turf
setting is to conduct an irritating drench or soapy flush. This
is done by putting two ounces of lemon-scented dish detergent in
two gallons of water and pouring the soapy solution over an area
which is about two feet on each side. The caterpillars will respond
to the soapy solution within two to five minutes. This technique
is particularly helpful for determining what stages (sizes) of caterpillars
are present. Do not sample on putting greens or other closely mown
turf at midday in the summer; the soapy solution may damage the
turfgrass. Visual
inspection can give an indication of the presence of caterpillars.
Take a close look at suspicious looking pock marks and look for
sheared grass plants on the perimeter. A rough estimate of the number
of damage spots (number of spots per square foot) is helpful when
comparing one area to another. Or make a small open frame, perhaps
one foot on each side, and toss it randomly in the general area
where cutworms are present. Count and record the number of damage
marks inside the frame. Black light traps attract adult moths very
effectively. Use the traps to determine when the adults first begin
to fly and when those flights peak in number. Cutworms are relatively
susceptible to several turf insecticides, as well as some biological
control agents. The key to successful
control is to apply a control agent (whether it is a biological
control agent or a traditional insecticide) when most of the
caterpillars
are still very small (around 6 mm (1/4 inch), if possible). Because
cutworms are nocturnal, traditional insecticide applications
should
be made as late in the day as possible. This will ensure that the
insecticide is as "fresh" as possible when the caterpillars
leave their burrows in the evening and begin foraging on the
surface.
This material should be watered in lightly, just enough to move
the insecticide off the blades and into the upper thatch. If
possible,
the area should not be mowed for one or two days after application.
One guideline for timing of applications is to make an application
two or three weeks after a peak in moth flight activity. This allows
time for the moths to lay eggs and for the eggs to hatch into small
caterpillars, which are the most vulnerable stage. There
are several biological control options which appear to work reasonably
well for controlling cutworms in turfgrass, as long as the biological
control agent is handled properly and applied with adequate water
and irrigation. Bacillus thuringiensis var. kurstaki,
available in a variety of commercial formulations, is a bacterium
which produces a toxin and paralyzes the gut of the caterpillar.
The bacterium will not kill the caterpillars quickly, but it does
cause the caterpillars to stop feeding, so damage should not continue
to spread after application. An
entomopathogenic nematode, Steinernema carpocapsae, is able
to seek out caterpillars and penetrate the host, where it introduces
a different bacterium. This bacterium causes a massive infection
in the host caterpillar. The nematode then reproduces inside the
insect cadaver and moves on in search of new potential targets.
Field trials in Ohio, New Hampshire and other places indicate that
this nematode can reduce caterpillar populations substantially.
However, the nematode is very sensitive to desiccation, so applications
should not be made at mid-day and should be watered in (at least
12 mm (1/2 inch) if possible) immediately after application. Some
perennial ryegrasses and fescues contain endophytes, which are fungi
that grow inside the grass plant. These endophytes produce two compounds,
one of which is toxic to some insects (including cutworms and webworms)
and one of which is toxic to grazing stock. The endophytes do provide
a level of resistance to caterpillar activity, and endophytic grasses
seem to experience considerably less damage than their non-endophytic
counterparts. So if a turf area is scheduled for renovation, consider
using endophytic cultivars (available in some perennial ryegrasses
and fescues). Besides being more tolerant to cutworms,
webworms and chinchbugs,
these cultivars often appear to be more drought tolerant. For more
information, see GreenShare Factsheet on Endophyte-enhanced
Grasses. Adapted
from the University of Massachusetts Extension, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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