We asked Paul Giordano, Ph.D., from Bayer’s Green Solutions Team, a few questions about the annual bluegrass weevil. Learn where the insect predominantly is today, if it’s spreading, how to treat for it, and a few other things in this Q&A.

In what areas does the annual bluegrass weevil predominantly cause issues?

Historically, the annual bluegrass weevil (ABW) has been a problem throughout much of the northeastern United States. Identification and early reports came from the Metropolitan NY area including southern CT, Northern NJ, Long Island, and Westchester Country. These areas are essentially the epicenter for ABW issues, but the pest is prevalent throughout New England, the Mid-Atlantic through Washington, D.C. and as far north as Montreal, Quebec in Canada.

Is the annual bluegrass weevil spreading into other areas? If so, why and where?

Yes, over the years reports of damage on both annual bluegrass and creeping bentgrass have shown the ABW to be spreading both westward and to more southern regions. Damaging populations are now frequently found west of Cleveland, OH and more recently reports from as far west as Cincinnati and Kentucky. ABW also seems to be well established in North Carolina, particularly in the higher elevation areas of the state. The expanding distribution of ABW is likely due to several factors including natural movement of the pest, changing/evolving weather patterns, and the forced movement of the pest via sod, equipment, golfers, etc.

What are the indicators of an annual bluegrass weevil issue?

Damage to closely mowed annual bluegrass surfaces, especially fairways and tees are the primary indicators. Damage from ABW typically begins along edges of fairways, greens, and tees, especially next to overwintering areas like tree lots. Symptoms begin as yellowish to browning spots or small dead patches that eventually coalesce into large areas as larvae develop. Stems break off easily from the root system of affected plants, which is one good indicator of an ABW issue. Symptoms are often mistaken with anthracnose or summer patch since they are localized to poa annua and typically do not affect surrounding bentgrass or other turf species.

How can we definitively diagnose an annual bluegrass weevil problem?

A sound diagnosis should occur by identifying the pest physically either in its adult or larval stage. Adult ABW are small 1/8 long dark gray/black beetles. The snout of the ABW is blunt compared to the bluegrass billbug’s extended snout. Adults lay eggs inside the whorl of the plant between leaf sheaths. Hatching larvae feed inside turfgrass stems and eventually burrow out of the stem and feed on crowns. Larvae are creamy white with a brown head, ranging from 1/32-inch-long as newly hatched (L1) to 3/16-inch-long fully developed (L5). Since these larvae reside in the upper thatch/soil interface, they are not very difficult to spot with shallow dig scouting or soap flushes.

What are the challenges we face when controlling the annual bluegrass weevil?

The ABW is one of the most difficult to control pests we face in turfgrass management. This is due to several factors:

  • First, the lifestyle and habits of the pest itself. Controlling adult ABW requires very specific timing and relies on the insecticide product to come into direct contact with the pest because adults don’t feed much, thus ingestion of systemic products isn’t a very effective option. Controlling larvae requires an effective chemistry that can get into the plant quickly and stick around a long time. This is often difficult and requires effective strategies to target the earlier larval stages in the pests development.
  • The second big challenge is the multiple generations of this pest per season. This causes major issues when trying to properly time applications with the appropriate chemistry. It also makes for prolific reproduction potential and greater genetic diversity in the population.
  • The third challenge, which is related to the first two in many ways, is the resistance to common insecticides. Many populations of ABW across the northeast and mid-Atlantic are now resistant to synthetic pyrethroids and increasingly insensitive to other chemical classes. These once effective products are no longer useful for many superintendents, leaving very limited options in an increasingly difficult regulatory environment.

When should we start our insecticide applications to control the annual bluegrass weevil?

In general, applications for adults should begin in the early spring. A good indicator for when population densities are at their height (and thus insecticide apps are most effective) is when forsythia is half gold/half green. When targeting first generation larvae, applications should begin in late April/early May, usually around the time rhododendron are in full bloom. Research with a new active ingredient from Bayer, tetraniliprole*, has shown great efficacy with good flexibility in targeting first generation larvae at all life stages (L1-L5).

What other insects do you see causing big problems this year that we can help control in the spring?

White Grubs are always somewhat elusive, especially coming off two very wet years. I expect to see spikes in grub populations as well as the continued movement/migration of different beetle species to new geographies. I also continue to see more issues with chinch bugs affecting different areas of turf around golf courses where historically they were never a problem. Getting away from older, broad spectrum insecticides and relying on some of the newer products has likely given rise to growing chinch bug populations. This is an interesting dynamic to keep an eye on moving forward. The best strategies for management involve understanding individual insect species life cycles and staying ahead of populations with timely and effective applications. Tailoring a program to your individual property, pests, and agronomic needs is always a better approach than the “one and done” mentality which opens itself to many uncontrollable variables.

What is the best way to treat for them?

The best way to treat for both ABW and other insect issues you may be dealing with is to plan your program with a good rotation of products, sound agronomics, and a scheduled approach that incorporates a keen understanding of the pest’s life cycles. Many different classes of chemistry can be used to target different stages of ABW development, but in general, the most effective and broad-spectrum class that can target both ABW and most other damaging turf insects on the golf course is the anthranilic diamide class. Bayer’s new insecticide (coming soon), is an exciting new member of the diamide class that has shown excellent efficacy on ABW, white grubs, caterpillar pests, and even chinch bugs. More info on tetraniliprole to come later in 2020, stay tuned!


*tetraniliprole is not yet registered nor offered for sale