Golf Course Management

JAN 2019

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106 GOLF COURSE MANAGEMENT 01.19 Toxicity and efficacy Figure 3. Toxicity (LC 50 in kilograms/hectare) of formulated bifenthrin (Talstar) (top left) and chlorpyrifos (Dursban) (top right) and efficacy (% control relative to untreated control) at select rates (1× is standard field rate; 0.112 kilograms/ hectare = 0.1 pound a.i./acre for bifenthrin; 1.21 kilograms/hectare = 1.0 pound a.i./acre for chlorpyrifos) determined in a greenhouse assay with formulated product and evaluated at 72 hours after treatment. Numbers above bars are resistance ratios (RR 50 = LC 50 resistant/LD 50 most susceptible) calculated with PB as the population most susceptible to bifenthrin and HP as the most susceptible to chlorpyrifos. NC, not calculated because the population was a baseline population. NA, not applied. susceptible PB and HP populations, but only 11% control of the moderately resistant GB population (Figure 3). Even at 3.0 pounds a.i./ acre, bifenthrin provided only 42%-53% con - trol of the resistant CN, EW and JC popula- tions and no control of the highly resistant LI population. Chlorpyrifos provided 73%-89% control of the pyrethroid-susceptible PB and HP populations at the standard field rate of 1.0 pound a.i./acre, but was ineffective (3%- 14%) against the pyrethroid-resistant popula - tions except for the JC population (48%) (Fig- ure 3). At 6.0 pounds a.i./acre, chlorpyrifos provided 42%-86% control of the pyrethroid- resistant populations. Conclusions is study expanded the geographic range of confirmed pyrethroid resistance in ABW adults from southern New England (5, 6) to include the New York metropolitan area, New Jersey and eastern Pennsylvania. Moreover, we observed two to three times higher resis - tance ratios (RR 50 ) and LD 50 s in the topical assay than had been observed previously (5). e study clearly showed cross-resistance not only within the pyrethroid class, but also to several other chemical classes, albeit at lower levels than for the pyrethroids. Several of the tested insecticides (spinosad, indoxacarb, clothianidin, chlorantraniliprole) had low toxicity against ABW adults in the topical assay. We suspected that the route of exposure is important for, at least, clothiani - din and chlorantraniliprole. Clothianidin and chlorantraniliprole have mostly systemic ac - tivity and low contact activity, which could ex- plain their low toxicity against ABW adults in the topical assay. However, even in the feeding assays, toxicity was low for clothianidin and indoxacarb and not significant for chlorantra - niliprole. ese compounds are recommended as larvicides for ABW management. For bet - ter understanding of cross-resistance patterns with these compounds, larval assays should be developed and conducted. e study showed that the resistance levels determined using the topical assay under opti - mal laboratory conditions were consistent with those made under more realistic conditions in potted grass in the greenhouse with formu - lated products. In the field, several routes of exposure could contribute to the compound toxicity: through direct exposure to the spray or through feeding on contaminated grass. 100 80 60 40 20 0 100 80 60 40 20 0 100 90 80 70 60 50 40 30 20 10 0 100 90 80 70 60 50 40 30 20 10 0 PB HP GB CN EW JC LI PB HP GB CN EW JC LI % control % control % control kg a.i./ha 40 35 30 25 20 15 10 5 0 100 90 80 70 60 50 40 30 20 10 0 Talstar – LC 50 (bifenthrin) 6 4 2 0 100 80 60 40 20 0 Dursban – LC 50 (chlorpyrifos) % control % control % control kg a.i./ha ABW populations Talstar 1x Talstar 10x Talstar 30x Dursban 6x Dursban 3x Dursban 1x NA NA NA NA NA NA NA NA NA NA NA NA NA NC 1.6 503* 63* 41* 51* 7.7* 1.3 NC 28* 3.9* 13* 13* 7.4*

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