Days and DD60s to Key Growth Stages in Modern Cultivars of Varying Maturities

Producers rely heavily on accumulated heat units (base 60 F) (DD60) and days after planting guidelines to estimate timing of applications and management practices for their crop.  Over time, changes in cultivars and technology have altered the type and quantity meteorological data collected. Based on these advances, it is likely that 1) guidelines required to reach key growth stages may be different now and 2) other environmental data could be included to strengthen estimates. The objectives of this study were to evaluate heat units and days required to reach six key growth stages of three cultivars of differing maturities to determine if guidelines should be updated and/or environmental parameters could be introduced to strengthen estimates. In 2017, a test was performed at the West TN Research and Education Center, Jackson TN. The three cultivars included were Deltapine (DP) 1612 B2XF (early maturity), DP 1646 B2XF (mid maturity), and DP 1555 B2RF (full maturity). The trial was planted in a randomized complete block with four replications. Based on initial observations, days to growth stage guidelines may need to be adjusted. Initial in-season guidelines of DD60s to a given growth stage appear to be relatively accurate, however, there is variation between the observed number of heat unit it took to reach 60% open and the expected accumulated heat unit based on the DD60 guidelines.