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June 17, 2002
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Black cutworm (Agrostis ipsilon) feeding activity
has been reported on several sites in Chicagoland (Photo
1). The night-flying cutworm moth (Photo 2) overwinters
in the southern states and migrates northward each spring
to lay eggs on turf or weeds. The eggs hatch in four to
five days and the larvae feed on putting greens at night,
with large fifth and sixth instars (# of molts) eating all
of the grass blades in a small, roughly circular area from
their burrow. The younger third and fourth instars frequently
live in taller grass near the green, and migrate 30 feet
or more onto the green at night to feed. Oftentimes, the
damage from feeding of these younger worms is trivial compared
to the damage caused by birds feeding on the cutworms.
Paying attention to farm reports may help us track this
pest, as black cutworms are also a very serious pest of
corn (Photo 3). The cool fronts that followed on
the heels of our unusually warm weather during the week
of April 15 resulted in "intense" captures of
migrating black cutworm moths in central Illinois. According
to a model for corn "cutting" (emergence of fourth
instars), which is based on these "intense" captures,
activity would have begun around May 19th for Knox county,
near Peoria. A report on June 14th stated that black cutworm
damage to corn had begun to have an economic impact on production
in central IL.
Aspects of management
Timing of mowing & insecticide applications
Studies have shown that greatest cutworm larval activity
occurs between 1:30 to 5:30 a.m. with most larvae burrowing
into the turf just before dawn. This indicates that a significant
amount of mechanical cutworm control could be gained by
mowing putting green surfaces an hour or so earlier than
usual at sunrise. Likewise, insecticide treatments for cutworm
control could be more beneficial if made earlier in the
morning. Also, since cutworm larvae can move a considerable
distance during a night (between 30 to 74 feet), it is important
to treat a 25-30 feet buffer zone around putting greens
to reduce the likelihood of cutworm reinfestation.
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Clipping removal
Nearly all of the eggs deposited by black cutworms on creeping
bentgrass greens are laid singly, on the tips of the leaf blades.
In one study, a single mowing at greens height (1/8 or 3/16 inch)
removed 75 to 97% of the eggs from a putting surface. However,
90% of the eggs on the discarded grass clippings survived. Therefore,
disposal of green and collar clippings away from
putting surfaces (at least 20-30 feet away) can significantly
reduce cutworm levels.
Aerification/Topdressing
It has become standard belief that aerification attracts black
cutworm larvae, resulting in greater damage than unaerified surfaces.
Observations in research plots by Williamson & Potter, however,
indicate that just as many cutworms established themselves in
the non-aerified parts of the plots than in aerified turf. A high
percentage of larvae however do exploit aerification holes as
burrows, which may lead to superintendents noticing more cutworm
damage after aerification. Aerification does not increase densities
of the pest, although it may increase the damage caused by fifth
or sixth instar larvae.
Although topdressing sand has been shown not to kill cutworm
larvae, in the same study by Williamson & Potter, cutworms
were consistently less abundant in topdressed plots than on plots
that were not topdressed. The thought is that the angular properties
of the sand may act as an irritant and has the potential to be
abrasive to the insect cuticle (similar to topdressing effect
on earthworms).
Photo #1. Characteristic damage by a fifth or sixth
instar cutworm larvae that has burrowed, and feeds along edges
at night.
Photo #2. Black cutworm moths fly at night and deposit eggs singly
on tips of grass blades.
Photo #3. Cutworm damage on corn, known as "cutting".
Feeding starts with 4th instar larvae.
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