Virginia Turfgrass Journal – Emeline Daly, Graduate student, School of Plant and Environmental Science – Turfgrass Management; Tom Kuhar, Ph.D., Professor, Department of Entomology; David McCall, Ph.D., Assistant Professor, Department of Plant Pathology, Physiology, and Weed Science
Annual bluegrass weevil (ABW) (Listronotus maculicollis) is the most damaging insect pest of golf course turfgrass in the northeastern United States (McGraw and Koppenhöfer 2007). The pest was discovered in New England in 1931, but until recent years, was largely confined to the northeastern states and not considered to be an issue in Virginia. That situation has changed drastically.
ABW Biology and Damage
While this weevil prefers to feed and lay eggs on annual bluegrass (Poa annua L.), it can also survive on creeping bentgrass (Agrostis stolonifera L.) if necessary. Annual bluegrass weevil is particularly damaging to short mowed areas of golf courses including tees, fairways, collars, and greens (McGraw and Koppenhöfer 2007).
Overwintering adult weevils (Fig. 1) will emerge in early spring and crawl to shortly-mowed grass and begin laying eggs that will hatch into larvae (Fig. 2) that feed on roots and root crowns. There are likely multiple generations of this weevil in Virginia based on multiple peaks of adult activity observed in 2019 from three Virginia golf courses based on weekly soap drenches on untreated turf plots (Fig. 3). Our data indicated three distinct peaks in ABW adults for each location. Because ABW can quickly cycle through their generations and continue to oviposit for a long time, often, multiple life stages are present at any given time once summer arrives. As a result, there is a difficulty with correct and effective application timing for management of ABW.
Distribution of ABW in Virginia
It is believed that ABW has been in Virginia since at least the mid-2000s, but the overall establishment and damage caused by this pest across Virginia golf courses has not been completely studied. Based on a survey by McGraw and Koppenhöfer (2017) of golf course superintendents in the northeastern states, several from Virginia reported ABW to be present on their golf courses. Thus, in 2019, we attempted to contact 203 golf course superintendents in Virginia with regards to whether they had a confirmed case of ABW at their golf course. Based on 49 responses, 36 golf courses (73.5%) responded with confirmed cases of ABW (Fig. 4), leaving 12 courses unaffected. Eleven of the 12 courses that reported not having ABW also have bermudagrass fairways, however 10 of the 12 courses have cool-season putting greens. There was only one course that reported no ABW and had an all cool-season turfgrass course.
Although annual bluegrass suffers the most damage from ABW, we have observed that creeping bentgrass is also damaged. Creeping bentgrass is a popular cool-season turfgrass that is widely used for golf course putting greens across America, as it can be mowed at significantly shorter heights. In Virginia, however, creeping bentgrass is used for more than just putting greens, and many courses use it for fairways, collars, and tee boxes as well. Because of Virginia’s transition zone climate and creeping bentgrass being a cool-season grass, keeping creeping bentgrass healthy throughout the summer is challenging enough without ABW threatening it. This summer specifically, Virginia golf courses were affected with damage primarily showing on fairways, tee boxes, and collars.
Insecticides and ABW
Effective control of ABW is a major challenge. Different insecticides are typically used to target adults and larvae. With regards to larvicides, some preventive larval control of ABW can be achieved with standard neonicotinoids or chlorantraniliprole (Acelepryn®) typically applied for white grubs. However, research has shown that these standard soil turf insecticides only provide about 50% control of ABW larval populations (McGraw and Koppenhöfer 2017). The aforementioned survey also reported that the most effective larvicides for ABW include: Ference, Provaunt, Matchpoint, and Dursban. Insecticides most commonly used for ABW adults include pyrethroids such as deltamethrin (Deltagard®), bifenthrin (Talstar®), cyfluthrin (Tempo®), and lambda-cyhalothrin (Scimitar®, Battle®). The organophosphate chlorpyrifos (Dursban) also provides great control of adult ABW.
Repeated and frequent use of pyrethroids on golf courses in the northeast has led to pyrethroid resistance development in populations of ABW. Because we do not know where our ABW populations on Virginia golf courses came from, it is possible that pyrethoid resistance genes may be present in our ABW populations already. Thus, monitoring for pyrethroid resistance will be a focus of research at Virginia Tech for the coming years. In 2019, we collected several populations of ABW adults from Virginia golf courses and tested them for pyrethroid susceptibility using a filter paper dip bioassay. With this bioassay, a typical spray tank concentration of bifenthrin was applied to filter paper discs and compared with water dipped control paper placed in Petri dishes. Weevil adults were placed in the dishes and were maintained on the treated filter paper. This assay should result in near-complete mortality of weevils in 24 hours as pyrethroids have rapid activity on insects leading to quick death. Based on ABW populations collected from Harrisonburg, Stanardsville, Nokesville, Crozet, Roanoke, and Blacksburg, mortality ranged from 32.5% to 100% with a lot of variation. This is an indication that our Virginia ABW populations may likely have different levels of pyrethroid resistance in them. This is indeed something that should be closely monitored. Pyrethroids are still a good option for adult control, especially given their cheap cost, but rotation of insecticide classes is strongly recommended as a resistance management tool. We plan to closely and more thoroughly examine this topic in the future in Virginia. Please contact us if you have a high population of ABW and you are interested in screening them for susceptibility to insecticides.READ THE ISSUE