P. G. Mulder, S. K. Seuhs
2003 Arthropod Management Tests  
Alfalfa weevil (AW): Hypera Postica (Gyllenhal) Fourteen chemical insecticide treatments were evaluated for efficacy in controlling Alfalfa weevil (AW) larvae infesting the first crop of a 3 yr stand of 'OK 49' alfalfa at the South Central Research Station, Chickasha, OK. Pretreatment samples indicated a population of 88 and 77 larvae/25 stems on the days when stubble and threshold treatments were applied, respectively. Insecticides were applied on 22 Feb (stubble) and 4 Mar (threshold) using a
more » ... CO 2 pressurized bicycle sprayer calibrated to deliver 20 gpa at 19 psi through seven, 11004 flat fan nozzles, when traveling at 3 mph. Treatments were arranged in a RCB design using plots 3.9 x 9.1 m in size, replicated four times. Sampling was conducted 3 and 7 DAT (stubble) and continued 4, 7, 21, and 28 DAT from the threshold application, by pulling 25 stems per plot and placing them in standard Berlese funnels to extract insects for counting. Dry matter yields were estimated for first harvest on 23 Apr by removing forage from a 1 x 5 m area in each plot using a flail-type harvester. Subsamples were dried for determination of moisture content and yields were calculated on a dry weight/acre basis. Weather conditions for the first four days after the threshold treatment were good for activity of insects with no rainfall and a mean daily high temperature of 71.0ºF. During the remaining days of Mar, a total of 1.86 inch of rainfall occurred and the mean daily high temperature was 63.1°F. The population density of AW was above the economic threshold at the time of stubble treatment; however, most larvae were quite small. Seven out of the next 10 DAT (stubble), temperatures reached lethal levels (< 20ºF) for AW larvae. Temperatures considered lethal to AW larvae were also attained twice after the threshold treatment. This accounted for the decrease in larval populations 4 and 7 DAT. No data were gathered 14 DAT due to rainfall in the area. Three weeks after the threshold treatment, conditions became quite favorable for weevil activity and subsequent hatch of larvae. Performance of insecticides applied at stubble was initially unsatisfactory; with approximately 50% control 4 and 7 DAT (stubble). These two stubble treatments (Warrior and Fury) did; however, suppress populations enough that the 2 days of lethal temperatures experienced after threshold treatment were sufficient in controlling the remaining larvae well below damaging levels. In fact, the alfalfa treated with Warrior-T (stubble) provided the best control of AW larvae and produced the greatest yields. AW populations peaked 28 DAT in untreated alfalfa; however, all treated alfalfa had significantly less numbers of larvae than the untreated. All alfalfa treated with Warrior-T, Fury, Baythroid and the Lorsban/ Pounce tank mix provided 75% control or better. Average percent control of AW larvae from 4 to 28 DAT ranged from a low of 8.7% for the low rate of Intrepid to a high of 90.5% for Warrior-T applied at stubble. Yield of alfalfa at first harvest ranged from 3974.3 lbs./acre in plants treated with Warrior-T at stubble, to 477.9 lbs/acre in the untreated plots. With the exception of alfalfa treated with Intrepid (both rates) or Tracer (lower rates), all treatments yielded significantly greater than the untreated, with a range of 169% (Tracer-high rate) to 732% greater (Warrior-T stubble). Alfalfa treated with Intrepid yielded significantly less than all other treatments except Tracer applied at the lower rate. No significant differences in yield were obtained between any treatments receiving a synthetic pyrethroid; and each of these plots yielded significantly better than Lorsban (alone), Furadan or Tracer. Alfalfa treated with Lorsban
doi:10.1093/amt/28.1.f6 fatcat:mvx5hokwmzbhpixfjebk2nryxi