Yield response and efficacy of registered and experimental fungicides for the control of target spot in cotton, 2016

摘要

On 9 May, cotton variety Phytogen 499 WRF was hill dropped behind a KMC strip till unit at a rate of 2.2 seed/row ft in a Malbis fine sandy loam (organic matter <1%) at the Gulf Coast Research and Extension Center in Fairhope, AL. The study received 0.5 in. water via a lateral irrigation system on 22 Jun, 27 Jun, 8 Jul, 11 Jul, and 1 Sep. Plots consisted of four 30-ft rows spaced 3.2 ft apart arranged in a randomized complete block with four replications. Velum Total was applied two days after planting with a single nozzle center over the row middle in 18 gal/A spray volume at 30 psi. Fungicides were applied with a Spider sprayer with 11002 tips mounted on a four row boom in 15 gal/A of spray volume at 55 psi at 3rd and 5th week of bloom on 19 Jul and 2 Aug, respectively, while the single application programs were treated at the 3rd wk of bloom on 19 Jul. The four applications of Headline + Bravo WeatherStik were made on 5 Jul, 19 Jul, 2 Aug, and 17 Aug. Target spot intensity was visually assessedon 20 Jul, 1 Aug, 15 Aug, and 31 Aug using a 1 to 10 leaf spot scoring system where 1 = no disease, 2 = very few lesions in canopy, 3 = few lesions noticed in lower and upper canopy, 4 = some lesions seen and < 10% defoliation, 5 = lesions noticeable and< 25% defoliation, 6 = lesions numerous and < 50% defoliation, 7 = lesions very numerous and < 75% defoliation, 8 = numerous lesions on few remaining leaves and < 90% defoliation, 9 = very few remaining leaves covered with lesions and < 95% defoliation,and 10 = plants defoliated. Defoliation values were calculated using the formula [% Defoliation = 100/(1+e(-(leaf spot scale value-6.0672)/0.7975))] (Li et al, 2012. Peanut Sci. 39:30-37). Cotton was mechanically harvested on 29 Sep. Statistical analysis was done on rank transformations of non-normal target spot defoliation and normal yield data. Non-transformed data are reported. Means were separated using Fisher's protected least significant difference (LSD) test (P<0.05).