Control of Southern Masked Chafer Grubs, 1991

Abstract

Abstract This study was conducted in a Kentucky bluegrass plot at the University of Kentucky Spindletop Research Farm, Fayette Co., KY. The established turf was on a Maury silt loam soil (fine-silty, mixed, mesic Typic Paleudalf), with pH = 6.2. Thatch accumulation was <0.25 inch. On 15 Aug we sunk 75, 8 inch diam cylinders made from PVC sewer pipe into the turf to a depth of about 7 inches. The turf was first irrigated with about 2 inches of water to soften the soil, after which a heavy (100 lb) tractor weight was used to drive the cylinders into the turf nearly flush with surface. Cylinders were about 12 inches apart, and were arranged in a randomized complete block with 5 replications and 15 treatments. Third instar SMC grubs were dug from an untreated rough on a local golf course on 19 Aug. Grubs were immediately taken to the experimental site and 15 active grubs were placed in each cylinder. Grubs that had not burrowed into the soil within 10 min were replaced. All cylinders except those receiving RH 3045 were treated between 9-11 am on 22 Aug, 72 h after grubs were introduced. Air temperature at the time of treatment was 75-80°F, with clear skies, 72% relative humidity, and 5 mph wind. Liquid formulations were diluted with water and applied as a coarse spray to the turf using a hand-held, triggertype sprayer. A total of 15 ml of diluted formulation was applied per cylinder. Growth regulator formulations (RH 5849, RH 0345) were mixed with Triton AG 98 surfactant (0.313 ml/liter). Nematode formulations were mixed with water and applied at a rate equivalent to 2 billion nematodes/acre. Granular formulations were weighed on a microbalance and sprinkled evenly into the cylinders. The turf within each cylinder was sprinkled with 50 ml of water immediately after treatment to wash the liquid formulations from the foliage and to provide a favorable microenvironment for the nematodes. Immediately after the final treatment was applied, the site was irrigated with about 2 cm of water. Because of a leaking package that was not noticed until the scheduled treatment date, the RH 0345 treatments were delayed for 5 d until a fresh sample had been received. These 15 cylinders were treated on 27 Aug in the manner described earlier. An additional 2 cm of water was applied to all cylinders following application of these treatments. Effectiveness of treatments was evaluated 21 DAT by removing each cylinder with a spade and examining the enclosed soil and turf for surviving grubs. Grubs, which consisted mostly of SMC with smaller no. of endemic Japanese beetle and May beetle grubs, were sorted by species. A small no. of cocoons of Tiphia sp., a parasitoid of SMC, were also recovered and counted. Data for live SMC, SMC & parasitoids, and total grubs were tested separately by ANOVA, and treatment means were separated by LSD test at the 5% significance level following square root transformation of the counts. Data are presented as original means (° SE).