Effect of Trinexapac-Ethyl Plant Growth Regulator on Red Clover Seed Crops.

The plant growth regulator trinexapac-ethyl (TE) has been used to increase seed yields and reduce lodging in temperate grass seed crops; however, little is known about the use of TE on clover seed crops. In six on-farm field trials, five rate and timing combinations were used to determine the effect of TE on red clover seed crops over two years. Treatments consisted of 240 and 480 g ai ha^-1 TE applied at stem elongation (BBCH scale 32), TE applied at bud emergence stage (BBCH scale 50) at 240 g ai ha^-1, 240 g ai ha^-1 split among the two timings, and an untreated control.  In both years, seed yield and weight were measured, and head counts, stem counts, and canopy height measurements were made in year two.  TE increased seed yields by 15 to 34 % compared to the control in year one and by 5 to 13% in year two. In both years a split application of 240 g ai ha^-1TE applied at both morphological timings was among the best treatments for increasing seed yield. Seed weight was inversely related to seed yield; treatments producing the highest seed yield had the lowest seed weight. Heads m^-2 were increased by TE. The 480 g ai ha^-1TE treatment applied at stem elongation reduced canopy height, and that tendency was evident in other treatments. Our results suggest that the cause of seed yield increase was increased production of seed heads and reduction in canopy height.  Field observations indicate that in addition to increasing seed yield, TE also promoted earlier maturation of the crop, allowing for a more timely harvest.