It’s a native insect
that has taken a liking to annual bluegrass. It’s a pest that started
small in the New York City area and has moved outward, and it’s so
damaging to its host plants that a turfgrass manager will want to get rid
of it as quickly as possible.
So says someone who has been studying the annual
bluegrass weevil (commonly referred to as ABW) for 30 years. Pat Vittum,
professor of turfgrass entomology at the University of Massachusetts,
Amherst, says that the 1/8-inch brown insect with the familiar weevil snout
has become a tremendous nuisance. The adult nibbles on Poa annua foliage, but it’s
the larval stages that really do a lot of damage.
|Photos by Masanori Seto.
|Larvae, here emerging from the soil, are the most
damaging to turfgrass.
|Adult annual bluegrass weevils add to the damage done
|Damage to Poa annuacan be extensive from the annual
bluegrass weevil, but controls are effective.
The adults deposit eggs in Poa annua between the outer leaf
sheath and the stem, and the relatively straight, white larvae feed until
they ultimately chew their way out. Then they continue feeding on the crown
of the plants. They will also feed a bit on bentgrass, but they prefer
annual bluegrass, even when it is cut short. The turf manager will see
patchy damage that resembles that made by anthracnose, and in New York
state, two to four generations can emerge.
“So you can have larvae feeding all summer
long,” Vittum says. Once there are overlapping phases of larvae and
adults feeding, the damage can be extensive. It is first noticed around the
edges of the turfgrass because ABW adults overwinter in surrounding leaf
litter and walk in to feed in the spring.
Vittum notes that there are several effective
treatments. The primary controls for ABW for many years were the pyrethroid
chemicals, but in areas where they have been used extensively, resistance
to the insecticides has developed. In some areas there is up to 95 percent
resistance in weevil populations. She still lists the pyrethroids in her
controls because in the pest’s outer range—as far south as
Maryland and north into Canada, with sightings in about 40
states—they can be effective.
The old standbys for her are bifenthrin (Telstar),
cyfluthrin (Tempo) and cyhalothrin (Scimitar or Battle). The first
application is made to curb-emerging adults, with a handy timing device in
New York being the period after the full bloom of local forsythia bushes
when the plants are acquiring green leaves. Repeated treatments may be
needed, and it is smart to rotate labels to avert resistance as much as
Another methodology is to attack the larvae after
hatching, Vittum says, and there are several options here. One is the use
of trichlorfon (Dylox), a wettable powder, as soon as you start seeing the
wilt on Poa from ABW, Vittum says. She notes that in the New York City
area, that will typically be around the first of June. Treatment should be
repeated as new larvae emerge and foliage wilts, about three weeks apart.
She has also tested the use of flowable spinosad
(Conserve) in place of trichlorfon, and found that it works when used in
the same methodology, but she doesn’t recommend it as consistently,
even though it may be preferred because it is a synthetic, bio-based
A wettable powder approved in 2007, indoxacarb
(Provaunt), is a new class of material that affects the insect’s
nerve function and is highly efficacious, Vittum says. This larvae killer
may also have to be applied more than once as subsequent generations emerge
during the summer. Again, the university’s recommendation is that
managers rotate usage of these larvae controls to avoid long-term
development of resistance.
Another new chemical, approved last year, is
chlorantraniliprole (Acelepryn). Vittum says this affects muscle control in
both adult and larval ABW, but has low toxicity to humans, pets and
wildlife. She has tested it for three years, and it has proven especially
deadly on the larvae.
“I’m very excited about this one,”
she says of chlorantraniliprole, because it is the only treatment that has
some carryover effects. A systemic pesticide, one application definitely
will kill two generations of the pest and may be good for the entire
season. This is the first year it has been widely available.
Vittum says that there is one other chemical approach
to ABW control, and that is compounds that are a combination of two
products. The first is Aloft, which is a mix of a neonicotinoid and a
generic bifenthrin. The other is Allectus, a blend of a neonicotinoid and
the bifenthrin Telstar. She says that neonicotinoids by themselves are not
She says there are also some cultural methods that can
help avert ABW through management. In general, they consist of minimizing
either the amount of Poa, or minimizing the amount of stress to the Poa.
Another way to reduce the number of emerging adults in
the springtime is to remove their winter shelters. This is usually plant
litter where adults overwinter by burrowing under leaves or other detritus
and gaining some protection from the cold. The litter under white pines has
been found to be a favorite hiding place, so particular attention should be
paid to removing it.
Nowadays, the weevil is a primary spring pest in a
wide area on the Eastern Seaboard and beyond, and a damaging one, but it
can be controlled, particularly with the use of the newest insecticides.
Don Dale resides in Altadena, Calif., and is a
frequent contributor to Turf. He has covered the green industry for more
than 10 years.