Boll abortion is increased when cotton (Gossypium hirsutum L.) experiences various stresses during its reproductive development that can consequently reduce lint yield. Before abscission, an increase in ethylene is observed which may be assumed to be the signal necessary to initiate abscission of that particular structure. It is desirable to prevent fruit loss that may be induced by the peak in ethylene before abscission. One potential option to cope with the loss of cotton reproductive structures is the use of ethylene inhibitors. Th us, the objective of this investigation was to determine the impact of 1-methylcyclopropene (1-MCP) on growth and yield components of cotton plants treated with ethephon (ethylene synthetic hormone) under fi eld conditions. Field studies were conducted as a randomized complete block design with four replications in 2007 and 2008. Treatments were three rates of 1-MCP in combination with a surfactant applied at mid-bloom. One day later, ethephon was applied as a source of abiotic stress. At harvest, the fruit set in the upper portion of the canopy was infl uenced by 1-MCP. It had a greater number of full size, yet immature bolls, which potentially could have had a positive infl uence in the lint yield. However, ethephon caused the highest lint yield since ethephon-treated plants had more open as well as total bolls in the lower canopy at harvest. In conclusion, 1-MCP improved growth and yield components mainly in the upper portion of plants canopy at harvest, but such an improvement was not converted into lint yield. V.A. da Costa, Dow AgroSciences LLC, 13147 Jackson Rd., Sloughhouse, CA 95683; J.T. Cothren, Texas A&M Univ., 370 Olsen Blvd., MS 2474, College Station, TX 77843; J.B. Bynum, Monsanto, 700 Chesterfi eld Pkwy. West, Chesterfi eld, MO 63017.

Maintaining profi table and sustainable production of cotton (Gossypium hirsutum L.) relies on improvements in management. Th e objective of this study was to determine the proper defoliation timing to optimize lint yield and fi ber quality through calculating heat unit (HU; DD15.5) accumulation beyond cutout, defi ned as fi ve nodes above white fl ower (NAWF = 5). Experiments were conducted in Burleson County, Texas, in 2003 and 2004, on a Weswood silt loam soil (fi ne-silty, mixed, superactive, thermic, Udifl uventic Halplustepts). Treatments were applied in a split-plot arrangement using a randomized complete block design with four replications. Th e main plots consisted of three nodal positions (NAWF = 3, 4, and 5) and the fi ve subplots were HUs (361, 417, 472, 528, and 583) accumulated beyond the corresponding nodal positions (NAWF), at which time a tank-mix of harvest aids was applied. Immediately before defoliation, 10 plants plot -1 were evaluated for percent open boll (POB) and nodes above cracked boll (NACB). Lint yield was detrimentally impacted in south central Texas when defoliation was initiated at 472 HUs beyond NAWF = 5. Defoliation at 60 POB resulted in as much as 29% more lint yield than defoliation based on the current benchmark of NAWF = 5 plus 472 HUs. Th is fi nding suggests NAWF = 5 is neither an indicator of the last eff ective fl ower population in all production locations, nor a proper guide for timing cutout on which end-of-season management decisions should be based in south central Texas. Abbreviations: DAT, days aft er treatment; HU, heat unit [(maximum temperature + minimum temperature)/2-15.5 in °C]; HVI, high volume instrument; NACB, nodes above cracked boll; NAWF, nodes above white fl ower; POB, percent open boll; POBD, percent open boll at defoliation; POBH, percent open boll at harvest.