Variety, seeding rate, and fungicide program impact on target spot defoliation, boll damage, and cotton yield, 2016

摘要

A wheat cover crop, which was drilled at a rate of 1 bu/A on 8 Dec 2015, was killed with 1 qt/A of Makazie on 16 Mar 2016. The study site was tilled with a KMC ripper/roller on 8 Apr. A 23 Mar broadcast application of 227 lb/A of 18-46-0 analysis fertilizer (41N-104P-0K) was followed by a broadcast application of 222 lb/A 0-0-60 analysis fertilizer (0N-0P-133K) on 18 Apr. A layby application of 23 gal/A of 28-0-0-5S liquid fertilizer (70N-0-0-12S) was made on 22 Jun. Broadcast applications of 1 pt/AFull-Bor (0.7 lb boron/A) were made on 6 and 18 Jul. On May 9, the cotton varieties Phytogen 499 WRF (susceptible) and Deltapine 1555 B2XF (tolerant) were hill dropped at seeding rates of 2, 3, and 4 seed/ ft behind a KMC strip till unit in a Malbis finesandy loam (organic matter <1%) at the Gulf Coast Research and Extension Center in Fairhope, AL. Weed control was obtained with a pre-emergent incorporated application of 1 qt/A Makazie + 2 pt/A Prowl H2O + 2 pt/A Cotoran on 9 May followed by a 17 Jun banded application of 0.1 oz/A Envoke + 2 oz/A Staple + 0.25% non-ionic surfactant under hoods, and a 5 Jul banded application of 2 oz/A Valor + 1 qt/A Diuron + 42 fl oz/A MSMA under hoods. Cotton growth was managed with broadcast applications of 8 fl oz/A Pix Plus on 21 Jun and 6 Jul followed by 12 fl oz/A Pix Plus on 18 Jul and 8 fl oz/A Mepiquat on 2 Aug. Cotton was prepared for harvest with an application of 1.5 pt/A Folex + 1 fl oz/A ET + 1 qt/A Boll Buster + 0.25% non-ionic surfactant on 12 Sep followed by 1 fl oz/A Diuron + 2 oz/A Dropp 50W + 0.25% non-ionic surfactant on 26 Sep. Stink bug control was obtained with 21 Jun and 18 Jul broadcast applications of 6.4 fl oz/A bifenthrin followed by a 2 Aug broadcast application of 6.4 fl oz/A Bidrin. The study received 0.5 in. water via a lateral irrigation system on 22 Jun, 27 Jun, 8 Jul, 11 Jul, and 1 Sep. A factorial set of treatments was arranged in a split split-plot with cotton variety as the main plot, seeding rate of 2, 3, and 4 seed/ft (28,000, 41,000 and 55,000 seed/A, respectively) as the split plot, and a fungicide program as the split split-plot treatment. Individual plots consisted of four 30-ft rows spaced 3.2 ft apart in four replications. Priaxor at 8 fl oz/A was broadcast with a Spider sprayer with 11002 tips mounted on a four row boom in 15 gal/A of spray volume at 55 psi at the 3rd, 5th, and 7th week of bloom on 18 Jul, 1 Aug, and 17 Aug respectively. A non-fungicide treated control was also included. Target spot intensity was visually assessed on 20 Jul, 1 Aug, 15 Aug, 31 Aug, and 8 Sep using to 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))]. Defoliation data collected on 8 Sep is presented in the table. Counts of open,locked, and rotted bolls were made on 3.2 ft of row in a border row of each plot on 28 Sep. Cotton was mechanically harvested on 28 Sep. Significance of factor effects was determined using PROC GLIMMIX procedure in SAS. Statistical analysis was done on rank transformations of non-normal target spot defoliation and rotted boll count data. Non-transformed data are reported. Means were separated using Fisher's protected least significant difference (LSD) test (P<0.05) unless otherwise indicated.