Seed moisture at physiological maturity in oilseed and confectionary sunflower hybrids in the northern U.S

Desiccating sunflower (Helianthus annuus L.) to hasten harvest has become common practice in the northern U.S. and can aid in reducing yield loss associated with severe weather, plant degradation, and bird predation. Current recommendations are to apply desiccants to sunflower at 35% or less seed moisture corresponding to physiological maturity (PM). However, evidence suggests PM may occur at higher seed moisture. Therefore, a 2-yr field study was conducted at Prosper, ND, and Morris, MN, with the objective being to model the dynamic relationship of seed dry matter accumulation to moisture content in sunflower seed of two high-oleic oilseed hybrids and one confectionary hybrid to estimate seed moisture content at PM. Between stages R6 and R9 (PM), seed samples were collected from capitulum at 4–7d intervals. Seeds were separated from the inner, middle, and outer concentric thirds of the capitulum for analysis. Average moisture content across middle and outer seed at PM for both oilseed hybrids was about 40% regardless of environment, but it was 50% for the confectionary hybrid. Inner seed lagged behind middle and outer zones in reaching PM, but only comprises about 11% of total seed on capitulum. Approximately 600–666°Cd were required for seed to progress from R6 to PM for the oil hybrids and 486–612°Cd for the confectionary hybrid. For both types of hybrids, PM occurred about 3d later in middle seed as compared to outer seed. Indeed, our results indicate modern sunflower hybrids can be desiccated at higher seed moisture than currently recommended without sacrificing yield loss due to not reaching PM.