Annual Bluegrass Weevil: What Happened in Spring 2025?

By Shaohui Wu, Ph.D.

The annual bluegrass weevil (ABW) appears to be an expanding issue in Ohio golf courses as the increasing reports of ABW damage (Figure 1) in low-cut turf in recent a few years. This weevil usually has 2-3 generations in Ohio, overwinters as the adult in tree lines, leaf liters and tall grasses, and migrates to nearby low-cut turf (preferably annual bluegrass, secondarily creeping bentgrass) in spring to start new generations. Due to fluctuating weather conditions in spring, there is a long time-span for adult populations to move out of hibernating sites, usually in March to April. Such a variation in the time of adult emergence leads to asynchrony in developmental stages and overlapping generation, making the control more challenging. Thus, most of the management programs target the first-generation adults and/or larvae, and monitoring of ABW stage progression is essential to the control success.

The commonly used monitoring tools include installing linear pitfall traps (Figure 2) on the paths of ABW migration (between overwintering sites and nearby low-cut turf), using soap flushing (0.6% to 0.8% soap water, i.e., one fluid ounce of soap mixed in one gallon of water) to track ABW adult numbers, and larval scouting from turf plugs with the saline extraction (with saturated salt water) or heat extraction method (1) (Figure 3). These allow for threshold-based applications to reach optimal control efficacy, while avoiding unnecessary sprays. Also, these methods can be used to scout ABW presence in new infestations, given that ABW problems can be misdiagnosed as disease or environmental stresses.

Our program has been closely monitoring ABW activities in Ohio, including sites in Cincinnati, Columbus, Cleveland and Toledo areas. Due to the inclement climate conditions in last winter, ABW adult migration from overwintering sites was 1-2 weeks delayed compared to the previous year. Also, usually the time of ABW population progression coincides with plant phenology; for example, ABW adult migration from overwintering sites begins when forthysia and daffodil are in full bloom and peaks when forthysia in half green: half gold and eastern redbud in early bloom at growing degree days (GDD, based 50°F) of 100-120. However, in this spring we noticed asynchrony in ABW progression and plant phenology, with plant growth being more advanced. For example, we observed peak ABW populations at the time of nearly full green of forthysia and full bloom of eastern redbud at GDD around 200. This suggests that plant indicators and GDD were not reliable for timing ABW stages this spring. This scenario, in combination with frequent rainfalls, made the timely application of ABW adulticides even more challenging, especially most of insecticides targeting adults had short residual periods. Superintendents complained that the optimal application window was too narrow, especially this spring, and many of them had to apply adulticides at a delayed schedule. Larvicides can serve as a remedy for such a situation. Actually, they may serve as a more reliable approach than adulticides, as it is the larval stage (especially late instars) that damages turf, and it can provide more informative control based on scouting of ABW larval stages and densities. Treatment options targeting ABW adults and larvae can be referred to the ABW factsheet (1).

Among our monitoring sites, we noticed dramatic differences in ABW population progression across Ohio in 2025. The Cincinnati and Columbus sites have had similar status, while the northern sites have been approximately 2 weeks behind (with the Toledo site being further behind of Cleveland). For example, overwintered ABW adults reached peak densities in mid-April in Cincinnati and Columbus areas and peaked in late-April in Cleveland and Toledo regions. This phenomenon has also shown in the following larval development as well as plant phenology. Such a geographic difference has also affected the treatment plans in different regions, with timings of application in northern areas 1-2 weeks behind of southern and central Ohio.  At this time, the first generation ABW have started to emerge as adults in Cincinnati and Columbus areas, while they are still in damaging larval stages in Cleveland and Toledo sites.

Despite that the majority of control efforts has focused to the first generation of ABW, the second and potentially third generations may also cause damage, especially when the control of the first generation fails, leading to accumulative population growths in the following generation(s). In attempting to manage ABW with multiple applications, it is critical to rotate products with different chemistries and modes of action to avoid potential development of resistance. Insecticide resistance has been known in this pest, especially after repeated uses of pyrethroids, which could also cause resistance problems to other insecticides.

For management of ABW with non-chemical approaches, microbial biopesticides based on entomopathogenic nematodes and fungi can be used for biological control. In particular, the beneficial nematodes can be used in combination with insecticides and may potentially alleviate insecticide resistance (2). For cultural control, removing mowing clippings can reduce ABW adults active on the turf surface (3), but the clippings need to be processed or disposed far from the play surface as the majority of weevils can survive mowing unharmed and return to low-cut turf. In general, healthy turf tolerates higher ABW numbers, and it is desirable to maintain a balanced management program for healthy turf growth and higher pest tolerance.

1. Rice, H., Wu, S. Annual Bluegrass Weevil. https://ohioline.osu.edu/factsheet/ent-0095
2. Koppenhöfer, A.M., Sousa, A.L., Kostromytska, O.S., Wu, S. 2025. Effect of pyrethroid resistance on the efficacy of entomopathogenic nematodes for the control of Listronotus maculicollis (Coleoptera: Curculionidae). Biological Control. 200, 105683. https://doi.org/10.1016/j.biocontrol.2024.105683
3. de Sousa, A.L.V., Kostromytska, O.S., Wu, S., Koppenhöfer, A.M. 2023. Optimizing sampling technique parameters for increased precision and practicality in annual bluegrass weevil population monitoring. Insects. 14, 509. https://doi.org/10.3390/insects14060509

Shaohui Wu, Ph.D. is an Assistant Professor and Turfgrass Health Specialist in the Departments of Entomology and Plant Pathology at The Ohio State University.