Golf Course Management

JAN 2019

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114 GOLF COURSE MANAGEMENT 01.19 Adulticides Adulticides were sprayed when densities of overwintered adults peaked, when Forsythia species were about 50% gold (bloom):50% green (leafing out), and growing degree days were 100-120 GDD 50 . Individual replicates consisted of 5-foot × 5-foot (153 cm × 153 cm) areas separated from adjacent replicates by 1 foot (31 cm) on each side. Treatments were bifenthrin, chlorpyrifos, indoxacarb and spi - nosad (Table 2). Adulticides were watered in with 0.04 inch (1 mm) of overhead irrigation. When used against the susceptible (HP, PB; Figure 1A) and moderately resistant (GB; Figure 1C) populations, all treatments sig - nificantly reduced ABW counts, with no sig- nificant differences among treatments (42%- 69%). No treatment provided significant control against the resistant (EW; Figure 1E) and highly resistant (LI; Figure 1G) popula - tions (Figure 1). No significant decrease in control in the resistant populations was observed for chlor - pyrifos when insecticide efficacy was com- pared among populations. Spinosad efficacy was significantly lower against the LI popu - lation than against the susceptible and GB populations, with the EW population not dif - fering from any other population. Bifenthrin efficacy was significantly lower against the LI population than all other populations. Indox - acarb efficacy was significantly lower against the EW and LI populations than against the susceptible and GB populations. Larvicides Early larvicides targeting the young lar - vae inside the plants were applied around the time of late bloom to just past bloom of dog - wood (200 GDD 50 ). Late larvicides targeting the older larvae outside the plants were ap - plied around the onset of full bloom of rhodo- dendron (400 GDD 50 ). Individual replicates consisted of 3-foot × 3-foot (92 cm × 92 cm) areas separated from adjacent replicates by 1 foot (31 cm). Treatments were the early larvi - cides chlorantraniliprole, cyantraniliprole and clothianidin, and the late larvicides chloran - traniliprole, cyantraniliprole, clothianidin, indoxacarb, spinosad and trichlorfon. Early larvicides were watered in with 0.1 inch (2.5 mm) of overhead irrigation, and late larvicides with 0.2 inch (5 mm). Against the susceptible populations (HP, PB; Figure 1B), all treatments significantly reduced ABW counts, with the late cyantra - niliprole application (93%) being the most ef- fective and the late clothianidin application (45%) the least effective. Against the moder - ately resistant GB population (Figure 1D), all treatments provided significant control, with spinosad (88%) being the most effective and the late clothianidin application (47%) the least effective. Against the resistant EW pop - ulation (Figure 1F), all treatments except the early clothianidin (5%) and early chlorantra - niliprole (19%) applications provided signifi- cant control, with the cyantraniliprole appli- cations (91%-94%) being the most effective. Against the highly resistant LI population (Figure 1H), only the cyantraniliprole appli - cations (76%-86%) and spinosad (65%) sig- nificantly reduced ABW counts. e only treatments not significantly af - fected by the resistance level were the early (83%-91%) and late (76%-94%) cyantranili - prole applications, spinosad (64%-88%), and the late clothianidin application (10%-47%). Indoxacarb (21%-80%) provided significantly lower control against the LI population than against other populations. e late chloran - traniliprole application (8%-64%) was signifi- cantly less effective against the LI population than against the susceptible and GB popula - tions. e early clothianidin application (6%- 57%), the early chlorantraniliprole application (17%-71%), and trichlorfon (25%-73%) pro - vided significantly less control against the LI and EW populations than against the suscep - tible and GB populations. Conclusions Our study clearly showed pyrethroid re- sistance in adult ABW under field condi- tions. Control of ABW by bifenthrin was significantly lower against the highly resis - tant populations than against the susceptible populations; however, bifenthrin showed no significant control of either the highly resis - tant or the resistant populations. Under green- house conditions, bifenthrin efficacy against adults from the same populations clearly de - clined from the susceptible to the moderately resistant and resistant to the highly resistant populations (2). Chlorpyrifos is not an effective adulticide alternative to pyrethroids against pyrethroid- susceptible and pyrethroid-resistant popula - tions. While the decline in efficacy against the resistant populations was statistically not sig - nificant, chlorpyrifos provided no significant control of resistant and highly resistant pop - ulations and only 50% control of susceptible populations. Under greenhouse conditions, chlorpyrifos efficacy against adults of the same populations clearly declined from the suscepti - ble to the moderately resistant and from the re- sistant to the highly resistant populations (2). When used against adults, indoxacarb and spinosad showed a similar decline in efficacy with increasing pyrethroid-resistance level in our study, but overall tended to be somewhat less effective than bifenthrin. In the present study, adulticides no longer provided signifi - cant control starting at a bifenthrin RR 50 of 95, but unsatisfactory performance of adulti - cides seems to become obvious to golf course superintendents, starting at bifenthrin RR 50 s of about 50. Among the larvicides tested, only cyantra - niliprole and spinosad were not significantly affected by resistance. Indoxacarb efficacy declined only against the highly resistant population, but it declined by 55%. Efficacy of chlorantraniliprole, clothianidin and tri - chlorfon declined by 32%-48% against the resistant population and even more against the highly resistant population. ese obser - vations are consistent with observations in previous field efficacy tests against suspected pyrethroid-resistant ABW populations (1). e pattern of insecticide efficacy against ABW populations with different resistance levels may vary somewhat between different golf courses based on their specific history of insecticide use. Nonetheless, the findings in this study combined with previous ob - servations (1, 2) show a robust pattern that can serve as a basis for recommendations for ABW control at different pyrethroid-resis - tance levels. In view of the serious resistance issues, the first recommendation for ABW management is to minimize synthetic insecticide applica - tions both in space and time as much as possi- ble, whether managing susceptible or resistant populations. is goal can be achieved more easily by following the second recommenda - tion, which is to shift control measures from management of adults to management of lar - vae. is allows for more informed decisions on the need for applications, because early lar - vicides allow monitoring adults past their peak densities in spring, and late larvicides allow monitoring of actual larval densities.

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