Abstract
Desiccant effectiveness in hastening sunflower (Helianthus annuus L.) harvest is based on research conducted for conventional sunflower hybrids; however, information is lacking regarding plant drydown response of more recently developed stay‐green hybrids to desiccation. Stay‐green and conventional sunflower hybrids were evaluated for plant drydown response to desiccant and control treatments in 2000 and 2001 at Carrington, Casselton, and Prosper, ND. The experiment was a randomized complete block arranged in a split‐split‐plot design with desiccation, hybrid, and harvest date representing main, sub‐, and sub‐subplot, respectively. Pioneer Hy‐Bred International oilseed hybrids ‘6338’ (stay‐green) and ‘63M91’ (conventional), and nonoilseed Seeds 2000 stay‐green hybrid ‘Bigfoot’ were evaluated for plant drydown response under natural (control) conditions and when desiccated with paraquat (1,1′‐dimethyl‐4,4′bipyridinium dichloride) applied at the labeled rate. Timing of desiccant application was based on visual characteristics of the capitulm and targeted at physiological maturity when achene moisture ≈ 350 g kg−1. Four harvest dates occurred at 7‐d intervals following desiccant application where achene, receptacle, and stalk moistures were evaluated. Results indicated hybrid achene‐moisture response across harvest dates was similar for the desiccated and control treatments, although desiccation hastened achene‐moisture loss to harvestable levels by 7 d. Harvestable achene and receptacle moistures were concurrent for the conventional hybrid 63M91, however, high receptacle moisture for the stay‐green hybrids 6338 and Bigfoot could prevent harvest even though achene moisture was at harvestable levels. Desiccation hastened hybrids 63M91, 6338, and Bigfoot receptacle drydown to harvestable levels by ≈7 d, however 63M91 reached harvestable moisture ≈5 d earlier than the stay‐green hybrids. Receptacle and stalk moisture differences indicated greater receptacle than stalk moisture differences between stay‐green and conventional hybrids. Desiccation is an important harvest management practice to hasten harvest especially for stay‐green hybrids where receptacle moisture determines harvestability. Increased levels of the stay‐green trait in sunflower may result in desiccation becoming a more common harvest management practice.
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