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ANNUAL BLUEGRASS WEEVIL

Jake Dosckocil, Entomologist1

CAUTION: These recommendations were developed for North Carolina and may not apply to other areas.
[General Information] [Biology] [Control] [Other Resources

Annual Bluegrass Weevil , Listronotus maculicollis (Dietz), Curculionidae, COLEOPTERA


Introduction

annual bluegrass weevil lateral viewThe annual bluegrass weevil (ABW), formerly known as the Hyperodes weevil, is a pest of turfgrass in the northeastern United States. This native beetle is most prevalent and injurious in low-cut, high maintenance turf such as golf course greens, tees and fairways. First reported damaging turfgrass in Connecticut in 1931, it has spread from the metropolitan New York area where it had been concentrated. Severe infestations are now experienced across the Northeast and into the Mid-Atlantic, including north to Maine and Quebec, west to Pennsylvania and Ontario, and south to Maryland. It was believed that the ABW was restricted to annual bluegrass (Poa annua) and isolated to the northeastern states.  In 2006-2007 it was identified in Ohio, West Virginia,Virginia, and in 2008 the first North Carolina report came from a golf course near Asheville. ABW larvae and adults feed primarily on annual bluegrass, often considered a weed by golf course superintendents since it is an aggressive invader of newly seeded stands of creeping bentgrass (Agrostis palustris).  Although annual bluegrass is its primary host, ABW has also been reported to feed on creeping bentgrass and perennial ryegrass (Lolium perenne). In areas where annual bluegrass is prevalent, high populations of weevils can cause substantial areas of dead turf that affect both the visual and functional quality of golf course turf.

Biology

annual bluegrass weevil stagesABW has a complete life cycle with 1-2 generations per year in the Northeast. The body of the adult is covered with fine hairs and scales, which are easily observed under magnification, and they possess a snout characteristic of all weevils. They measure 3-4 mm (~1/8 in.) long, about the same size as black turfgrass ataenius, or about 1/3 the size of a billbug, another common turfgrass weevil. In addition to overall size, ABW can be differentiated from billbugs because their antennae arise from the tip of the snout, rather than the base.  Newly emerged adults, known as “callows” or “tenerals,” are chestnut to brown in color, making the young adults distinguishable from mature adults that are dark grey to black. Adults feed on grass blades, carving out notches on the edges, but cause insignificant damage.  Weevils over-winter mainly as adults in litter under pine trees and clippings deposited in roughs along the sides of fairways.  They begin to migrate from turf areas to these sites in early autumn and return in early spring.

During oviposition, females chew holes in the outer leaf sheath and insert eggs between the sheath and the stem. Eggs are oval in shape, measure 0.25 x 0.8 mm (1/100 x 3/100 in.) and hatch in 4-5 days. Young larvae live as stem borers, feeding on tissue within the protection of the stem and fill it with sawdust-like frass. When they outgrow the stem, older larvae drop to the soil surface where they shape crude burrows and forage out to chew on surface roots and crowns.

Larvae are legless with bodies that are straight to slightly curved. This makes them easily distinguished from white grubs, which have six legs and are “C”-shaped. Their bodies are creamy white in color with a well-defined brown head capsule. The larval stage contains five instars ranging in size from 1 mm (1/25 in.) long for first instars to 4.5 mm (1/6 in.) long for fifth instars. Small larvae are the size of P. annua seeds while large larvae are the size, shape and color of rice grains with brown heads.  Fifth instars mature to a prepupa within the top 1 cm of the soil. This stage is active for 2-5 days and builds a cell in which the inactive pupa will reside for 6-14 days before a callow adult emerges.  Prepupae, including the head capsule, are creamy white, while pupae resemble adults, but remain creamy white until they darken with maturation and take on the brown coloration of new adults.

Damage

ABW has an affinity for close-cut P. annua although; it will feed on perennial ryegrass and creeping bentgrass in those same close-cut habitats. As such, home lawns, athletic fields, and turf habitats other than golf courses and tennis courts are not affected, even though ABW and P. annua might be present.

Most damage is attributed to the larvae feeding on and killing stems. A single individual can injure up to 20 stems. Stems are weakened and broken due to the boring activities of the young larvae. Older larvae reside at the soil or thatch surface where they feed on the crowns. ABW injury is generally expressed as growing areas of yellow and brown patches.  It is usually first noticed around the collar and perimeter of the greens, tees or fairways. ABW damage can be superficially similar to the injury caused by some other pests and diseases. Therefore, be sure to use the “tug-test” as part of your diagnosis. A light tug on affected grass will pull up stems if they have been weakened by the activity of larvae. It may also reveal the frass, or excrement, left behind after their feeding.  Damage from second generation ABW occurs in late July until early August.

Monitoring

ABW is challenging to monitor due to its small size. In the spring, mower baskets can be monitored for adults because they are picked up along with clippings. This can be a useful way to stay on top of when adults are appearing in the spring, and, with more careful monitoring, on which areas of the course they are most prevalent. Some areas of the course may always harbor ABW so it is a good idea to monitor consistently those historically affected areas from year to year.

A more site-specific approach to monitor adults is to pour a soapy water solution on the turf surface (1-2 tablespoons of lemon-scented dish detergent mixed in 2 gallons water). This irritant forces adults to emerge from the thatch and ascend to the surface where they can be counted. Shallow soil core sampling or simply digging around at the soil surface / thatch interface will reveal older larvae and pupae. If more detailed information is desired, larvae of all sizes (even stem boring stages) will float to the surface when an infested core is submerged and agitated in a saturated salt solution. This is a good way to confirm that your adult controls were adequate; if too many larvae are found, the application may have been poorly timed to suppress adults and another application against the developing population may be necessary.

Damage thresholds are considered to be 30-80 larvae/sq. ft for the spring generation. Given summer heat stress, thresholds drop to 20-40 larvae/sq. ft for the summer generation. Nevertheless, field experience indicates that action may have to be taken at thresholds as low as 5-10 larvae/sq. ft in order to avoid injury and minimize the threat of the subsequent generation.

Management

Before an informed decision about any management technique can be made, scouting must be conducted to gather information on which life stages are present, where infestations are located, and whether those populations are large enough to warrant intervention.  Cultural management options include proper nutrition and irrigation, which often helps mask symptoms of ABW damage. Converting from a susceptible turf species to one that is tolerant to ABW is also an effective management strategy. Overwintering adults are sometimes very abundant in white pine litter, leading some golf courses to remove pine litter or even remove stands of white pine trees. Tree removal is not recommended, because these sites are not actually preferred locations for overwintering. Weevils will overwinter elsewhere.

Few natural enemies to ABW are known. Biological control has been achieved with late spring applications of a parasitic nematode (Steinernema carpocapsae) as well as the fungus Beauveria bassiana. Studies with wasps (Microctonus aethiopoides and M. hyperodae) that parasitize ABW have provided minimal control.  At this time, controlling ABW with insecticides seems to be the most effective strategy.

Timing for traditional chemical control of adults with spring applications has been based on a plant phenological indicator. The most widely used is the period that occurs between Forsythia  full bloom, and dogwood, Cornus florida, full bract. It is better to make the spring application a little late rather than a little early so aim for the time when Forsythia is in full bloom and has already acquired many new leaves (i.e. “half gold/half green”). Choose a relatively insoluble insecticide that stays in the thatch where adults are active. Synthetic pyrethroids (Bifenthrin, Cyfluthrin, lambda-Cyhalothrin, Deltamethrin) are the best options. Combination products containing clothianidin + bifenthrin are also effective. Water-in the application lightly to move the material off the leaves. Widespread fairway applications are usually not necessary. It should be sufficient to limit applications to periphery sprays along historically susceptible greens, collars, tees and fairway perimeters. These products generally provide over 85% control. With this in mind, failure of a well-timed pyrethroid application can occur due to resistance. Researchers in the Northeast are working to determine how widespread pyrethroid resistance is.  Spinosad can be an alternative when the use of pyrethroids results in less than adequate control. Combination insecticides are also helpful to reduce resistance. Work done recently at the University of Massachusetts has shown that spinosad applied as a curative treatment targeting larvae provided control better than 90% when applied in June.  This approach is a break in the traditional treatment of ABW but can provide the desired control.

For preventive ABW control in chronically infested sites, a long residual insecticide such as imidacloprid or halofenozide should be applied before egg hatch to control larvae. However, these chemicals typically only reduce populations 40-60%.  Long-residual, preventatively-applied insecticides used for white grub control often provide less control of ABW than the curatively-applied pyrethoids that target adults.  Since water dilution rates, rainfall, mowing and other factors affect control, it is important to follow insecticide label instructions.

References

1. Peck, D.C., M. D. Diaz, and M. Seto. 2007. Annual bluegrass weevil turfgrass fact sheet. New York State Integrated Pest Management Program.
2. Rothwell, N., and P.J.Vittum. 2003. The annual bluegrass weevil: A little weevil causing big problems in the Northeast. USGA Green Section Record. Vol. 41 (1): 6-7.
3. Vittum, P.J., M.G.Villani, and H. Tashiro. 1999. Turfgrass Insects of the United States and Canada, 2nd ed. Cornell University Press, NY. 422pp.

Other interesting links-

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service.
Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

© 2009 NC Cooperative Extension Service

ENT/ort-146 April, 2009
1Prepared by Jake Doskocil, Dept. Entomology, NCSU. Currently with The Scotts Co. LLC, Columbus, OH.
Photo credits: S. Bambara. Lifestage drawing from Vittum et al. Acknowledgements: R. Brandenburg and S. Bambara for their suggestions; D. Stephan for identification.

Web page last reviewed January, 2011 by the webperson.