The annual bluegrass weevil (Listronotus maculicollis) has established a reputation as a devastating turfgrass insect pest of golf course turf. This weevil is found in the northeastern, mid-Atlantic and Midwest regions of the U.S. and the eastern provinces of Canada.
In spring, flightless adults walk from overwintering sites in leaf litter and tall grass onto short-mown turfgrass areas to feed and mate. The female will chew a notch in the stem of a turfgrass plant and insert eggs into the stem or under the leaf sheath. The eggs hatch into larvae, and these larvae are stem borers for the first three instars. The larvae feed externally on the crown during the fourth and fifth instars.
The emerging overwintering adult populations are denser than subsequent generations, and the resulting damage in spring from first generation late-instar larval feeding is usually most severe. Damage is particularly noticeable in turf mowed at ≤ 0.5 inch (≤ 1.27 centimeters), especially sites with high populations of annual bluegrass (Poa annua). Therefore, research was conducted to investigate mowing practices for control of the weevil.
The first study wanted to find out if mowing could physically remove the adult weevils. Mature annual bluegrass was obtained from a putting green, placed in the greenhouse, and mowed at 0.100, 0.125, 0.150 or 0.250 inch (2.5, 3.2, 3.8 or 6.4 millimeters). Adults were marked with ultraviolet (UV) ink for detection during mowing events, with five adults inserted per turf core. The reel mower was fit with a basket to capture clippings and any weevils that were ejected by the blades. Adult mortality was based on the number of weevils collected through a combination of manual examination of the turf core and clippings, and the use of UV light to detect the marked weevils. Each mowing treatment was replicated 60 times.
Mowing did not affect adult survival, as most adults collected from each mowing height were alive. However, the highest percentage of adults were removed from the lowest mowing height (0.100 inch; 2.54 centimeters), and very few adults were removed with the higher mowing heights. Daily mowing of putting surfaces may lead to fewer weevils establishing in these areas, but weevil damage is more likely to occur in higher heights-of-cut such as collars and fairways where weevils can lay eggs and larvae feed without being affected.
The second study examined mowing height and egg laying behavior, particularly where eggs are placed. In a field study, annual bluegrass was mowed at 0.100, 0.125, 0.150 or 0.300 inch (2.5, 3.2, 3.8 or 7.6 millimeters). Turf plots were enclosed on all sides with a linear pitfall trap to prevent adult weevil movement into other plots. The number of eggs deposited and the location (i.e., inside or outside the stem, between the leaf and stem) were observed. Each mowing treatment was subjected to 20 mating adult pairs.
Adult weevils were capable of ovipositing at all mowing heights, but fewer eggs were deposited inside the stems at the lowest mowing height. Instead, eggs were placed haphazardly on top of the turf canopy in the lower heights-of-cut, where they may be prone to predation by ant and ground beetles, or subject to abiotic losses (i.e., dessication). This offers a plausible explanation of why weevil establishment is rare on low-mown greens.
The third study evaluated larvae ability to develop into damaging stages (i.e., fourth and fifth instars) in low-mown turf in controlled field studies. Turf plots were subjected to the same mowing heights as the second study. Each mowing treatment was replicated nine times which allowed for multiple larval stage assessments over time.
Larvae populations and instar development were not affected by mowing height. Therefore, putting surfaces mowed as low as 0.100 inch (2.5 millimeters) run the risk of being damaged by annual bluegrass weevil.
The researchers concluded that annual bluegrass weevils’ presence, establishment and foraging ability in putting greens is uncommon at the lower mowing heights. Adult weevils can survive mowing and are viable among clippings, so clipping management is important, so they don’t re-invade the site.
Source: Czyzewski, B.D., and Benjamin A. McGraw. 2017. Mowing height influences Listronotus maculicollis (Coleoptera: Curculionidae) oviposition behavior and mechanical removal from golf course putting greens, but not larval development. Journal of Economic Entomology 110(5):2165-2171
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading. He is a 25-year member of GCSAA.