Golf Course Management

JAN 2019

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104 GOLF COURSE MANAGEMENT 01.19 343 (LI). (Resistance ratio or RR 50 = LD 50 or LC 50 of resistant population/LD 50 or LC 50 of the most susceptible population.) Adults from the HF population and the PB (LD 50 0.005) and HP (LD 50 0.011) popu- lations were highly susceptible to bifenthrin. No control failures have been reported from these three locations where frequency of pesti - cide applications was relatively low. erefore, these populations were used as susceptible contrast in most of our assays to calculate re - sistance ratios. Adults from all other locations, where dif - ficulties in controlling ABW with synthetic insecticides had been reported, demonstrated moderate to high levels of resistance to bifen - thrin, ranging from an RR 50 of 31 (GB) to an RR 50 of 343 (LI). e LD 50 s for λ-cyhalothrin (0.001-0.363 microgram/insect) were, on av - erage, about half of those for bifenthrin and followed a very similar pattern with respect to resistance levels (RR 50 s = 18-324) (Figure 1). e populations that showed resistance to bifenthrin also had significantly higher LD 50 s for chlorpyrifos (RR 50 range = 3.3-15.3), spi- nosad (RR 50 range = 2.5-7.7) and clothiani- din (RR 50 range = 4.2-9.7) compared with the most susceptible population (Figure 1). However, the RR 50 s were much lower than for the pyrethroids. e LI population also was clearly the least susceptible to chlorpyrifos and spinosad, but for populations at the other locations, the ranking of resistance levels fol - lowed a pattern different from that for the py- rethroids. Feeding assays Mortality from indoxacarb and chloran- traniliprole in the topical assays was too low (≤20%) to allow calculation of LD 50 s. erefore, feeding assays were conducted to determine resistance levels of ABW popula - tions to these active ingredients. Clothiani- din is systemic and has demonstrated higher toxicity if ingested. erefore, clothianidin, which showed relatively low toxicity in the topical assay, was also included in the feed - ing assays. Two susceptible (HP, PB) and five resistant (GB, CN, EW, JC, LI) popula - tions were tested. A small disc (0.16 inch [4 mm] diameter, 0.04 inch [1 mm] thick) pre - pared from cutworm diet was placed in the middle of each petri dish (3.5 inches [9 cm] diameter) lined with one moistened (1 mil - liliter tap water/dish) filter paper. Diet discs were treated with 10 microliters of acetone or active ingredient solution in acetone. Ten adults starved for 24 hours prior to assays were introduced per dish. ere were three dishes for each of five concentrations (rang - ing from 0.1 to 30 milligrams a.i./milliliter) of each insecticide for each ABW popula - tion. Mortality was assessed at 24, 48 and 72 hours after weevil introduction. In the feeding assay, chlorantraniliprole was not toxic enough to cause significant ABW mortality even at the highest rates, and the data were thus not presented. Py - rethroid-resistant populations showed sig- nificantly increased tolerance to indoxacarb with the highest RR 50 for LI (9.7) and the lowest for GB (2.8) (Figure 2). Toxicity of clothianidin was similar to that observed in the topical assay, except that the LC 50 s at the most susceptible (PB) and most tolerant sites (CN) were three and two times, respectively, higher in the feeding assay than in the topical assay (Figures 1, 2). Toxicity of formulated bifenthrin and chlorpyrifos in greenhouse assays Five concentrations of bifenthrin (Talstar, range 0.003-60 pounds a.i/acre [0.003-67.2 kg a.i./hectare]) and chlorpyrifos (Dursban, range 0.003-15 pounds a.i./acre [0.003-16.8 kg a.i./hectare]) were tested against spring- generation adults from two susceptible (PB, HP) and five resistant (GB, CN, EW, JC, LI) populations. Ten adults were introduced into each pot with P. annua established from seed in pasteurized sandy loam soil mixed with sand. After two hours, treatments were ap - plied using a Generation III Research sprayer at a spray volume of 80 gallons/acre (756 li - ters/hectare). Treatments were lightly watered in with 0.05 inch (1.3 mm) irrigation. Pots were covered with ventilated lids and left in the greenhouse. After 72 hours, pots were submerged in lukewarm water to extract the adults. ree replications were arranged per treatment. LC 50 s for formulated bifenthrin and chlor- pyrifos were comparable to results obtained in the topical assay with technical-grade ac - tive ingredients. Populations HP and PB were highly susceptible. RR 50 s were the highest for the LI population (503), intermediate for the EW, JC and CN populations (41-63), and lowest for the GB population (7.7). For chlor - pyrifos, the LI population had the highest RR 50 (28), with RR 50 s for the other resistant populations ranging from 3.9 to 13 (Figure 3). At the standard field rate of 0.1 pound a.i./ acre, bifenthrin provided 60% control of the This sprayer system was used in the greenhouse assays.

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