Target spot intensity and yield of two cotton varieties impacted by Headline application number

摘要

The study site was tilled with a KMC ripper/roller on 19 Mar. On 24 Apr, 180 lb/A of 11-0-33 fertilizer with 10 lb/A sulfur and 0.5 lb/A boron was broadcast. A layby application of 23 gal/A 28-0-0-5S (70-0-0) liquid fertilizer was made on 19 Jun. On 9May, Phytogen 499 WRF and Deltapine (DPL) 1252 B2RF cotton varieties were hill dropped behind a KMC strip till unit at a rate of 3 seed/row ft in a Malbis fine sandy loam (organic matter <1%) at the Gulf Coast Research and Extension Center in Fairhope,AL. Weed control was obtained with a pre-emergence incorporated application of 1 qt/A Roundup Weathermax + 2 pt/A Prowl H2O + 2 pt/A Cotoran followed by a 12 Jun broadcast application of 1 qt/A Roundup Weathermax + 1 pt/A Dual Magnum II and a post-directed application of 2.5 pt/A MSMA + 1 pt/A Diuron on 27 Jun with a hooded sprayer. A banded application of the plant growth regulator Mepichlor at 8 fl oz/A on 17 Jun was followed by an application of 12 fl oz/A Mepichlor on 27 Jun and 8 oz/A Mepichlor + 6fl oz Bidrin on 17 Jul. Cotton was prepared for harvest with an application of 1 fl oz/A ET + 3 fl oz/A Takedown followed by 1 qt/A Diuron + 2 oz/A Dropp 50W + 21 fl oz/A Ethephon on 8 Oct. The study was not irrigated. The experimental design was a split plot with cotton variety as the whole plot and Headline 2.09SC application number as the split plot treatment. Individual split plots consisted of four 30-ft rows spaced 3.2 ft apart. Four replications of treatments were included. Headline 2.09SC at 12fl oz/A was applied with a Spider sprayer with 11002 tips mounted on a four row boom in 15 gal/A of spray volume at 45 psi on 10 Jul, 31 Jul, 12 Aug, and 27 Aug, which corresponds to the 2nd, 4th, 6th, and 8th week of bloom, respectively. Headline 2.09SC programs included application(s) at 1) 2nd; 2) 2nd & 4th; 3) 2nd, 4th, and 6th; 4) 2nd, 4th, 6th, and 8th week of bloom. A non-fungicide treated control was included. Target spot intensity was assessed on 15 Jul, 29 Jul, 14 Aug, 26 Aug, 9 Sep, and 24 Sep 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. Cottonwas mechanically harvested on 14 Oct. Significance of interactions was done using the PROC GLIMMIX procedure in SAS. Means were separated using Fisher's protected least significant difference (LSD) test (P<0.05). Since the cotton variety x fungicide interaction for target spot intensity and yield are not significant, data presented for each variable are pooled by variety and fungicide program.