Headline application timing impacts target spot control and yield of two cotton varieties

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 499WRF and Deltapine (DPL) 1252B2RF 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-emergent 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-direct 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 applications of 12 fl oz/A Mepichlor on 27 Jun and 8 oz/A Mepichlor + 6 fl ozBidrin on 17 Jul. Cotton was prepared for harvest with an application of 1 fl oz/A ET + 3 fl oz/A Takedown + 1 qt/A Boll Buster on 26 Sep 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 factorial arranged in a split plot with cotton variety as the main plot and fungicide program as the split plot treatment. Individual split plots consisted of four 30 ft rows spaced 3.2 ft apart. The study had four replications. Fungicides were applied with a Spider sprayer with 11002 tips mounted on a four row boom in 15 gal/A of spray volume at 40 psi at pinhead square, 1st, 3rd, 5th and 7th week of bloom on 18 Jun,16 Jul, 31 Jul, 12 Aug, and 27 Aug, respectively. Timing treatments included two applications of Headline 2.09SC at 9 fl oz/A at 1) pinhead square & 1st week of bloom, 2) 1st & 3rd week of bloom, 3) 3rd & 5th week of bloom, and 4) 5th & 7th week of bloom. For the full season Bravo WeatherStik at 1.5 pt/A and Headline 2.09SC 9 fl oz/A + Bravo WeatherStik at 1.5 pt/A programs, applications were made on 2 Jul, 16 Jul, 31 Jul, 12 Aug, and 27 Aug. A non-fungicide treated control was included. Target spot intensity was visually assessed on 15 Jul, 29 Jul, 14 Aug, 26 Aug, 9Sep, 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. Data collected on 24 Sep is displayed in the table. Cotton was mechanically harvested on 14 Oct. Significance of interactions was determined using the PROC GLIMMIX procedure in SAS. Statistical analysis on target spot intensity was done on rank transformations of data, which were back transformed for presentation. Means were separated using Fisher's protected least significant difference (LSD) test (P<0.05). The cotton variety x fungicide interaction for target spot intensity on 24 Sep was significant and fungicide data are presented by cotton variety. Since the cotton variety x fungicide interaction for yield was not significant, pooled data are presented.