BILLBUGS Contents:
Introduction
Billbugs consist of a number of
different species within the Curculionidae or
weevil family. Insects in the weevil family are noted for their
beak-like snouts as adults, legless larvae, and their boring-type
damage.
Identification
Billbugs (Sphenophorus spp. ): Four important species of billbugs will attack
turfgrasses. Adults are gray, black or brown usually 5-12 mm in
length depending on species. These ground colors are often
obscured by soil that adheres to pits, punctures and grooves on
the cuticle. Once cleaned the surface sculptures on the pronotum
and wing covers can be used to separate the various species.
Billbugs are weevils with a unique characteristic snout. All four
billbug species have the antennae attached at the base of the
snout nearest the eyes. The other major grass feeding weevils have
the antennae attached near the tip of the snout.
The two most common species in Maryland are the bluegrass billbug (S. parvulus Gyltenhal) and the hunting billbug (S. venatus vestitus Chiltenden). The Sphenophous larva is white, legless and with a brown head capsule. The larvae of the various species are nearly identical and almost impossible to identify. Eggs are sausage shaped, clear to creamy white. The female inserts 10-20 eggs individually into the stem or leaf sheath at the base of the plant.
Distribution
Wherever grasses are grown in the
U.S. one or more of the Sphenophorus
species can be found.
Hosts
The bluegrass billbug is a
potential key pest wherever Kentucky bluegrass is grown. This
species also attacks perennial ryegrass, fescues and timothy. The
hunting billbug although found feeding in other grasses, is most
serious in zoysiagrass and bermudagrass. Any turf with accumulated
thatch offers the adult good over wintering harborage and
protection from predators. In home landscapes, accumulations of
leaves, pine needles and bark mulches adjacent to turfgrass also
provides good protection. Any landscape site that conserves heat
during the early spring such as a sidewalk, driveway, asphalt
pathway and concrete or brick walls encourage females to
congregate and deposit higher numbers of eggs in the adjacent
turf. Other turf sites in full sunlight are preferred over shaded
area for the same reasons.
Life Cycle
Both species have identical one
year life cycles. The adult overwinters and begins egg laying in
the spring. They feed and disperse for a short period and begin
egg laying in May and early June in the Mid-Atlantic states and
Ohio. The adult female chews a small hole in the grass stem or
leaf sheath and deposits an egg.
The first instar larva stage feeds inside and hollows the stem. This feeding activity results in a light tan powder or fine sawdust like material to accumulate inside the stem. The same material is evident in the crown area where the growing larva exits into the soil. The presence of this material helps separate billbug damage from disease injury. The older larva feeds on roots at the thatch-soil interface. A partial overwintering second generation will occur in the southern states. In warmer climate older larvae can be found in soil throughout the year. This results from a prolonged egg laying period in the spring and late summer.
Damage
Damage is two-fold and both
species are similar in their habits. Early damage occurs in late
June into mid-July. At this time the larva tunnels into the stem
and crown causing the
stems to brown and die. A good
diagnostic sign of billbug injury is the compacted frass found
inside the dead stems. Older larvae feed
on roots. These larvae are often
intermixed with white grub larvae in the soil.
The collection of 6-8 adults in a five minute search period is considered a moderate infestation. These observations are made on sidewalks, driveways and patio areas around the house. The adult rarely flies but usually walks from lawn to lawn. However this sampling method is limited because of the daily variation in adult activity caused by differences in weather, site microclimate, sampling time during the day and landscape topography. Not all the billbugs are active at one time and most are inactive on cool, rainy days. If scouts make observations on one of these "off" days, the population estimate will be suspect.
The pitfall trap sampling method is preferable to the above mentioned visual counts. The pitfall trap samples populations throughout the adult activity period from early April to late May when egg laying begins. This technique provides a more accurate population estimate because the traps function even when the scouts can't. When trap counts range 2-5 adults per day, moderate, spotty turf injury can be expected in 2-3 weeks. Whereas, severe losses can occur when adult counts exceed 7-10 per day over several days sampling.
Ideally, pitfall traps should be used in combination with degree-day heat unit models and visual scouting. The degree-day models help predict developmental activity and thus can better estimate these peak activity periods during the years with abnormal growing seasons. Using a threshold temperature of 50 degrees Fahrenheit adult activity is first noticed at 280-352 degree-days and egg-laying beginning after 560-624 degree-days.
Biological-Biorational
Control
Natural occurring fungal diseases
within the Beauveria genera
frequently kill adults during cool, prolonged rainy periods in
spring and late fall. No fungal agents are registered in the U.S.
This may change within 3-4 years as overseas products are tested
and labeled for the U.S. market.
Several commercial strains of entomophathogenic nematodes have been evaluated Currently the nematode Steinernema carpocapsae and marketed as Vector has labeling for billbug control. This product needs to be irrigated in after application with best results occurring in the early morning or evening periods.
Cultural Control
Watering and fertilizing to
stimulate regrowth of infested turfgrasses is an important
cultural method for recovery. Varieties of grasses with extensive
rhizome and underground stem systems are better able to recover
from billbug damage. Tall fescue and perennial ryegrasses appear
to better tolerate billbug damage but once severely damaged they
may not recover. Avoid using Kentucky bluegrass cultivars in
problem situations that historically host high billbug
populations. Some genetic resistant varieties are available but
these may have limited geographic usefulness because of other
agronomic factors. However endophyte-enhanced resistance within
tall fescues and perennial ryegrass make these grasses excellent
choices for high risk billbug areas.
Chemical Control
An adult control program offers
the best option when billbugs become habitual problems. Two
behavior characteristics strengthen this choice. Since the adult
female rarely flies they migrate slowly into uninfested turf area
each spring, and once established, they require a pre oviposition
period of 2-3 weeks before egg laying. Secondly they have only one
generation a year. Thus an April to mid-May application of an
insecticide will kill the adult females before they lay eggs and
reinfestations may not reoccur for 2-3 years after
treatment.
Insecticides which are labeled for adult control of billbugs are as follows:
Pyrethroids: Tempo, Battle, Scimitar, and Talstar
Larval control is difficult since young billbug larva will feed within the stem before they eventually move into the soil to feed on the root systems. Merit, a new insecticide and which has systemic activity, has shown good control for the larva stage of billbugs.
Other insecticides which are labeled for billbug larvae that are in the soil are as follows:
Carbamates: Sevin and Turcam+
*Not registered for golf course turf and sod farms.
+Have restrictive labeling
Billbug grub control methods in our experience have been less satisfactory than the adult treatments.
by Dr. Lee Hellman, Department of Entomology and Dr. J. Kevin Mathias, Institute of Applied Agriculture