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11.16 GOLF COURSE MANAGEMENT 77 Optimal management programs for annual bluegrass weevil populations with different insecticide resistance levels Albrecht M. Koppenhöfer, Ph.D. Olga Kostromytska, Ph.D. Shaohui Wu, Ph.D. The annual bluegrass weevil (ABW) is a se - rious and expanding pest with a demonstrated ability to develop resistance to a range of in - secticides under the commonly used manage- ment regimes (that is, multiple applications of synthetic insecticides per season). Through previous research, we have developed a bet - ter understanding of the degree and scope of insecticide efficacy in laboratory and green - house experiments. In the ongoing study, we continue these studies in a two-pronged attack on the resistance issues. Insecticide resistance studies in t e field We tested the efficacy of standard insec - ticides against ABW adults, young larvae and midsize larvae on golf course fairways at courses with about 2×, 30×, 100× and 340× pyrethroid resistance compared with our most susceptible population at Rutgers Hort Farm No. 2. Dursban (chlorpyrifos, Dow AgroSciences) applied at 1 pound a.i./ acre (1.12 kilograms/hectare) was no replace - ment for pyrethroids for adult control. Con- trol with Dursban averaged 50%, 39%, 24% and 15% at the 2×, 30×, 100× and 340× sites, respectively. Talstar (bifenthrin, FMC Corp.) applied at 0.1 pound a.i./acre (112 grams/hectare) averaged 70%, 67%, 43% and 10% control at the 2×, 30×, 100× and 340× sites, respectively. Ference (cyantranili - prole, Syngenta) applied at 0.16 pound a.i./ acre (179 grams/hectare) was not affected by pyrethroid-resistance level or timing (versus early larvae, which coincide with late-bloom dogwood; or versus midsize larvae, coinciding with full-bloom rhododendron), and provided 68% to 99% control (88% overall average). Figure 1. Densities of annual bluegrass weevil developmental stages in early June (peak fourth to fifth instar) in two golf course fairways (A, B) treated with BotaniGard (BG), Talstar (Tal), and a combination of the two (BG+Tal). In both fairways A and B, Talstar at the full rate was applied once just before peak densities of overwintered adults, and BotaniGard was applied just before peak adult densities and again one week later. In fairway B, there were two additional treatments: Talstar was tested at half-rate applications one week apart (Tal2) and in combination with BotaniGard (BG+Tal2). Means with the same letter did not differ significantly (P > 0.05). An asterisk indicates a synergistic interaction. Densities of ABW developmental stages (report) 0 5 10 15 20 25 30 35 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 UTC BG Tal BG+Tal UTC BG Tal BG+Tal Tal2 BG+Tal2 A No. of ABW/square foot No. of ABW/square foot a a a b* a ab ab b* a b 40 40 45 45 50 50 55 55 110 120 110 120 B