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.
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 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.
cutworm (R.A. Casagrande)
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.
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.
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.
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.
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.
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.
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.
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
from the University of Massachusetts Extension, 1999