R E S E A R C H U P D AT E S F R O M
FIG. 1. Weekly number of annual bluegrass weevil adults (blue solid line) per ft2 and total number of immatures (orange dotted line) from three 2.5-inch soil core plugs recorded from a golf course in central VA during several collection dates (X-axis) in 2021.
Detecting Annual Bluegrass Weevil in Virginia Golf Courses By Alejandro Del-Pozo Ph.D., David McCall Ph.D. and Tom Kuhar Ph.D.
A
nnual bluegrass weevil, Listonotrus maculicollis or ABW, is one of the key pests affecting short-cut bluegrass and creeping bentgrass turf on golf courses, especially at greens and tees. Previous research at Virginia Tech has already showed that ABW is present and widespread in VA. Scouting efforts during 2021 added golf course locations with ABW infestations, including sites in Virginia Beach. In fact, an active scouting program is still highly recommended for superintendents. To detect the presence of this weevil, it is suggested to use flushes with soapy water, and also collect soil core plugs to extract immatures using the salt float method. These two videos made by Syngenta Turf, www.youtube.com/ watch?v=Zds1Z1_pYmc for soap flushes and www.youtube.com/ watch?v=4M1rEMYP388 for salt floats, provide information on how to get started and perform these two sampling procedures. Using these traditional methods, the Turf Entomology team at VT continued to document the phenology of this pest across VA in 2021. The main commonality found from our scouting efforts indicates that adults, coming from overwintering, are highly active during the first two weeks of April, with a subsequent peak of immatures during early May (Fig. 1). However, the highest adult densities are usually found during late July to mid-August in western VA, meanwhile the peak of adult activity in central VA can be recorded during mid-July. It is imperative to know when ABW adults are present in the golf course, where local factors among areas in the Commonwealth such as weather and resident ABW population might influence its phenology. Additionally, if managing immatures, it is also important to know when small larvae will be documented. The information provided by an active scouting program in a golf course will aid to properly time insecticide applications targeting either adults, immature of both. Since scouting with these two methods might end up being time consuming, the Turf Entomology team is exploring additional techniques for detecting ABW and its early signs for damage. The team is using light reflectance as a proxy to determine how stressed turf could be while having an active ABW infestation under golf course conditions. Graduate student Shannon Bradley has already started collecting this spectral data from two ABW-infested golf courses in VA. So far, there is a clear and consistent difference between signatures from good-health [GH] turf plots when compared to poor-health / ABW-infested [PH] plots (Fig. 2). From our data, stressed turf by ABW was not reflecting as much light as its healthy counterpart in the 530–570 nm range (green section of the visible light spectrum) as expected. In contrast, ABWinfested turf reflected more light in the 660–690 nm bands (red section) when compared to healthy turf. The team will be exploring up to 12 different spectral indexes, looking for one or a set of them that will highly correlate with ABW visual counts and damage scale. From the data collected in July and August 2021, there were
FIG. 2. Light reflectance profiles from good-health [GH] turf plots (black solid line) and from poor-health / ABW-infested [PH] plots (gray dotted line) collected from a golf course in central VA on July 20th, 2021.
significant differences between the NDVI (Normalized Difference Vegetation Index) calculated from GH vs PH plots (GH = 0.78 ± 0.01, PH = 0.70 ± 0.02; df = 9.24, t = 3.28, P = 0.0092), indicating that this index might aid to accurately discern between healthy and ABW-infested turf. The main goal for this research is to create a library of light reflectance signatures for both healthy and ABWinfested turf, targeting to detect any issue related to this pest by remote sensing and the use of drones. Ultimately, one flight of a drone could potentially provide information on the effects of multiple stressors in a golf course, including insect infestations, disease outbreaks, or water and nutrient management status.
22 | VIRGINIA TURFGRASS JOURNAL January/February 2022 www.vaturf.org
