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University
of Rhode Island GreenShare Factsheets
Billbugs Spenophorus
parvulus
Coleoptera: Cuculionidae
There
are several species of billbugs which occur on turf in New England,
but the bluegrass billbug is probably the most common species on
lawns. As its name suggests, its primary host is Kentucky bluegrass,
but it also attacks perennial ryegrass and fescues. Occurrence of
the bluegrass billbug in New England is generally very sporadic,
but when it does occur, it can cause severe damage. Adult
billbugs are grayish or black weevils. The body is not quite 6
mm (1/4 inch) long, with a relatively broad thorax ("shoulder")
which extends about a third of the total length. A fairly long,
narrow
snout extrudes from the head. Larvae are white or cream-colored
with brown, hardened head capsules. They have no legs but can
move
through the soil and thatch by pushing and pulling like worms.
They range in size from 2 to 6 mm (1/16 to 1/4 inch) as they
mature. The
bluegrass billbug completes one generation per year. Billbugs overwinter
as adults in semi-protected areas (in surface litter around
buildings,
in leaf litter, or in hedgerows). Adults emerge during the first
warm periods in the spring and begin to move to suitable turf
sites.
Adults can be observed crossing paved areas on sunny days in late
May or early June. The adult females lay eggs in June, which
hatch
into small larvae and feed within the grass stems for about two
weeks. As they grow, they molt and move to the bases of plants,
where they feed on the crowns. Eventually they also feed on
roots
and rhizomes. In areas where bluegrass billbug larvae have been
feeding actively, there will be accumulations of "frass," or insect
excrement, which is white and has the texture of fine sawdust. The
"frass" serves as positive identification of bluegrass billbug damage.
Feeding damage usually is evident along the edges of paved areas
and may resemble salt damage (except that billbug damage appears
in July). Eventually the damage may spread throughout the turfgrass
expanse. Larvae continue to feed for most of the summer and then
pass through a brief pupa ("resting") stage in the soil in late
August. Young adults then emerge and seek out suitable overwintering
sites during September and October. Thus the primary period for
damage is in late July and most of August, while the larvae are
feeding actively. Bluegrass
billbug adult activity is surveyed most easily by observing paved
areas near bluegrass or primarily bluegrass lawns on sunny days
in late May or early June. When two or more adults are observed
per minute, damage along the adjacent turf area can be expected.Thus,
if you observe the pavement for five minutes and see 12 billbugs,
you can expect to see billbug damage about six weeks later. The
estimate for tolerance levels (thresholds) for larvae varies widely,
but a reasonable starting point for moderately maintained turfgrass
in New England appears to be 8 to 12 larvae per square foot. Several
cultivars of lawn-type turfgrass have demonstrated resistance to
bluegrass billbug feeding. The resistance appears to be associated
with the presence of an endophytic fungus, which grows inside the
plant and makes it unpalatable to a variety of surface-feeding insects.
Endophytes have not yet been discovered in any Kentucky bluegrass
varieties but are available in several perennial ryegrass and fescue
cultivars. Unfortunately
most bluegrass billbug problems become apparent in late July or
early August as the larval population increases in size and feed
more voraciously. Once the population increases in stage, it is
too late to obtain acceptable levels of control. Studies in Pennsylvania
and Ohio have shown that timing of applications is particularly
difficult because there are at least four species of billbugs which
may be present and that timing for each is a little different. Some
turf managers like to target adults (in late April or May), but
the period of time when those adults are present and vulnerable
appears to be seven to ten days, so there is plenty of opportunity
for improper timing. The most reliable timing of application for
New England appears to be June, targeting some small larvae. Several
insecticides have shown reasonable activity against billbugs. In addition
to endophytic ryegrass and fescues, turf managers can consider using
entomopathogenic nematodes on billbugs. Field trials in the Northeast
have been very limited so far, but trials in Alabama and Ohio looked
promising. Entomopathogenic nematodes cause disease in the target
insects. The nematodes are packaged such that they can be sprayed
through a standard hydraulic sprayer. The species which looks most
promising (Steinernema carpocapsae) is very sensitive to
desiccation, so it should not be applied in drying conditions (midday
in midsummer, low humidity, and breezes) and should be irrigated
immediately after application. Applications probably should be timed
to coincide with emergence of small larvae, usually late June or
early July. 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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