This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, firstname.lastname@example.org
Sorghum Physiology & Management IV
This is the fourth of five physiological Sorghum Tips AgriLife is sharing over fall and winter of 2017-2018. See the library of previous Sorghum Tips at http://texassorghum.org/sorghum-tips for the previous information.
The Grain Sorghum Panicle (Head)
Sorghum panicles or heads exhibit a range of appearance depending on the hybrid and growing conditions. Panicles can range from compact (tight) to semi-open (Fig. 1) to open (loose) (Fig. 2) depending upon the length of the primary branches of each spikelet. Compact panicles have short primary branches and loose panicles have long primary branches. Panicle length and seed number per panicle are dependent upon when floral initiation takes places. Adequate soil moisture and less stress will result in larger panicles and higher yield potential. Adverse conditions during flowering including hot dry winds can lead to reduced pollen viability with fewer grains (‘blasting’) developing.
Morphology driven sorghum management consideration #4:
Environment and feeding insect potential may influence hybrid choice of panicle type.
Loose panicle hybrids that are fast growing and dry down rapidly are generally more preferred in areas with higher humidity and greater panicle feeding insect pressure. Tight panicles may enable insects and worms to better hide from feeding birds. Likewise, tight panicles also reduce insecticide penetration for feeding worms and other insects that may move into the head (e.g., feeding sugarcane aphids). Furthermore, tight panicles are more likely to develop grain molds in humid environments due to poor drying within the panicle. This was an example given to me recently from Haiti where most U.S. grain sorghum hybrids suffer from tighter heads.) Most Texas producers probably don’t consider panicle type, but accept whatever hybrid is best adapted or recommended for their area regardless of panicle type (or plant or grain color).
Grain Sorghum Flowering
Flowering of grain sorghum panicles begins from the tip and moves downward, completing flowering in 4 to 7 days for typical size sorghum heads. The larger the head, the more likely producers should check grain maturity as defined by black layer at the bottom of the head (as well as on tillers, which may be later to bloom by several days vs. the main panicle).