Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 4214 IREC Farmers' Newsletter No. 196 — Summer 2016 Did pesticide treatments reduce thrips numbers? In the 2014–15 season, two sprays of sulfoxaflor were applied before the high-threshold sprays were triggered. Neither showed any effects in thrips control at the Whitton site (Figure 2). In fact, larval thrips numbers continued to increase despite two sprays. In an effort to bring down thrips numbers at Whitton, fipronil was applied in lieu of sulfoxaflor at the time when the first high-threshold sprays were triggered. Whereas at the Darlington Point site, the sulfoxaflor was used as the thrips numbers were not so high. Following this round of sprays, larval thrips numbers in treated plots were significantly reduced compared with unsprayed plots at both sites. At Whitton, thrips numbers again hit the 10 thrips/plant threshold so both plots were sprayed and thrips numbers, although remaining above the threshold, were less than a quarter of the numbers of the unsprayed plots. At Darlington Point the overall numbers were lower and only the 1 thrips/plant plots were re-sprayed and only that plot remained significantly lower than the other treatments at the end of the establishment phase. In 2015–16 rainfall prevented either site being sprayed at the 1 thrips/ plant threshold. The Whitton site, planted 9 October 2015, was sprayed with a single fipronil spray when thrips numbers were around 10 thrips/plant and the plants were at 5–6 leaf stage (Figure 3). The thiomethoxam seed treatment significantly reduced larval thrips numbers in the first monitoring period but not subsequently. The Darlington Point site was planted a week later and initially became waterlogged, so on 15 November when the first foliar fipronil spray could be applied, the plants had only two leaves and significant cupping, and thrips numbers were greater than 10 thrips/plant for almost two weeks prior. The thiomethoxam seed treatment had no noticeable effect on thrips numbers. The thrips numbers dropped post-fipronil spray in all plots even the unsprayed seed treatment plots, although there were significantly less thrips in both sprayed fipronil treatments (approximately 2 versus 5 thrips/plant). The second fipronil spray on the 2-spray plot again reduced thrips numbers and again both fipronil treatments had lower numbers of thrips compared with the unsprayed thiomethoxam seed treatment plots. There were high levels of variability in both the cotton plants and thrips numbers at the Darlington Point site. 0 1 2 3 4 5 6 7 8 9 10 28 Oct 15 9 Nov 15 23 Nov 15 Larval thrips per plant Monitoring dates 2015 Fipronil + Cruiser Fipronil Unsprayed control a b a a a a a a b Fipronil Figure 3. Average numbers of larval thrips in different threshold treatments at Whitton 2015–16. Error bars show the standard errors. Arrows indicate spray timing. Note that the significance difference in treatments on 28 Oct 2015 was with log transformed data. 0 20 40 60 80 100 120 140 21 Oct 27 Oct 3 Nov 13 Nov 20 Nov 1 Dec Larval thrips per plant Monitoring dates 2014 Transform @ 1 thrips/plant Transform @ 10 thrips/plant Unsprayed T1 T1 Fipronil (T1),T10 T1,T10 a a b a a b Figure 2. Average numbers of larval thrips in different threshold treatments at Whitton 2014–15. T1 = sulfoxaflor (Transform) applied at 1 thrips/plant, T10 = sulfoxaflor applied at 10 thrips/plant. Error bars show the standard errors. Arrows indicate spray timings. There was no effect on yield results in two seasons of the experiment, suggesting growing conditions have been adequate to allow plants to recover from early season thrips damage. Thrips on the underside of the cotyledon of a cotton plant. Monitoring dates 2014 Monitoring dates 2015 Larval thrips per plant Larval thrips per plant