Soil Ph and Irrigation Effects on Residual Control of White Grubs with Triumph 4 E, 1991

Abstract

Abstract This study was conducted in a Kentucky bluegrass plot at the Univeristy 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 = 5.8. Thatch accumulation was <0.25 inch. Experimental plots for separate tests of residual effectiveness of isazophos (Triumph 4 E) as affected by irrigation and soil pH were established in late Jun. A split-plot design with 5 replications was used for each test. For the irrigation test, there were two levels of watering (3" total per wk in two watering periods, or natural rainfall). Main plots (6 × 5 ft) were divided into two subplots (3 × 5 ft) maintained under the different irrigation regimes. For the pH test, each main plot (9 × 5 ft) was divided into three subplots (3 X 5 ft). Subplots were treated either with ammonium sulfate to lower soil pH, calcium hydroxide to elevate soil pH, or were left untreated. Two applications of ammonium sulfate (0.9 lbs/15 ft2) were applied to acidic subplots on 3 Jul and 8 Jul. Calcium hydroxide (1.8 lbs/15 ft2) was applied to basic subplots on 3 Jul. Soil samples were taken from each-plot at the beginning (11 Jul) and end of the test (15 Sep) and analyzed for pH. On 19 Jul, we sunk five, 8 inch diam cylinders made from PVC sewer pipe into each subplot to 7.5 inch depth in both tests. Cylinders represented microplots which were either left untreated or treated with isazophos (Triumph 4 E) at 2 lbs AI/A. Non-watered microplots in the irrigation test were covered with aluminum foil before the rest of the site was irrigated. Treatments were applied 19 Jul, 2, 16 Aug, or 3 Sep, representing 6 wk, 4 wk, or 2 wk before grubs were present, or 3 Sep, after grubs were added (remedial treatment). Third instar JB were collected from an untreated golf course rough on 1 Sept, and 10 active grubs were placed in each cylinder. Grubs that had not burrowed into the turf within 10 min were replaced. Treatments were prepared by mixing 1.52 ml of isazophos in 1 liter of water, and applying 10 ml to each microplot using a trigger-type hand sprayer. Posttreatment irrigation (0.75 inch) was applied to all microplots immediately following isazophos treatments. The cylinders were harvested on 15 Sep. The soil was carefully examined in large plastic pans and the no. of surviving grubs was counted.