Maturity Elongation of Mid-Season Upland Cotton Varieties Through the Use of Pyraclostrobin and Azoxystrobin Fungicides

Cotton (Gossypium hirsutum L.) is subject to stress and yield reducing factors throughout the growing season. The loss of Delta and Pine Land 555 Bollgard® Roundup Ready® (DPL 555 BR) cotton in September 2009 removes a variety from the commercial market that proved to be a useful tool for farmers. This true full-season variety gave producers in regions of the U.S. Cotton Belt, where long growing season windows are established, the opportunity to take full advantage of extended growing days until harvest. The potential to delay the maturity of a mid-full season upland cotton variety, to that of the established full season variety, DPL 555 BR, may be possible through the determent of stress with fungicides. A two-year field study was conducted at the Texas AgriLife Research Farm in Burleson County in 2008 and 2009. The study evaluated the impact of pyraclostrobin, Headline®, and azoxystrobin, Quadris®, fungicides and their effect on yield and maturity after application to a mid-full season upland cotton variety, Stoneville 4554 Bollgard II® Roundup Ready Flex® (STV 4554 B2RF). These fungicides, along with commercially available tank-mix compounds, were applied to the study area at two defined growth stages: Early Bloom (EB), and Early Bloom +14 days (EB+14). Data analyzed over the years of both studies indicated statistical and numerical differences for fungicidal treatments. Statistical differences were noted in measurements throughout the years of both Study 1 and Study 2. Final plant mapping measurements and fiber properties for both studies failed to show improvements of increased nodes or plant height, as well as the measurements obtained from HVI analysis, due to the additions of either pyraclostrobin or azoxystrobin compounds. Combining these strobilurin fungicides with the labeled compounds of mepiquat chloride or mepiquat chloride did not yield results detrimental to plant characteristics measured in these studies. The treatment timing of EB+14 that contained the pyraclostrobin compound increased lint yield versus the untreated control by 213 kg ha^(-1)