Evaluation of Trinexapac-Ethyl to Reduce Lodging for Hybrid Rice.

Hybrid rice technology is offered by private companies in the United States; however, adoption has not exceeded 20% of the United States planted area. Reasons for low adoption in the southern USA rice belt is partly due to hybrids being taller and more prone to premature lodging and grain shattering compared to inbred cultivars. Trinexapac-ethyl, a gibberellic acid (GA) biosynthesis inhibitor stops production of GA19 to GA20 in the GA pathway. The result is growth inhibition. A two-year study (2007 and 2008) was conducted at the Delta Research and Extension Center, Stoneville, MS, to determine if a foliar application of trinexapac-ethyl would reduce plant height and decrease lodging for hybrid rice. Additionally, the experiment sought to determine if trinexapac-ethyl affected grain yield and milling quality for hybrid rice. Eight treatments which consisted of combinations of two preflood N rates (134 and 202 kg N ha-1), two topdress N timings [panicle differentiation (PD) and panicle emergence (PE)] where 52 kg N ha-1 was applied, and two rates of trinexepac-ethyl (0 and 85 ml ai ha-1) applied at 14 days after PD were included with replication. Averaged across years, preflood N rates, and topdress N timings, trinexepac-ethyl reduced plant height from 117 cm to 94 cm. Lodging was not observed in 2007; however, in 2008, an interaction among main effects was present for lodging. No lodging was observed where trinexepac-ethyl was applied; however, lodging ranged from 28 to 83% of the plots depending on PF N rate and topdress N timing where no trinexepac-ethyl was applied. Grain yield or whole milled rice was not affected by trinexepac-ethyl. However, grain yields were greatest when 202 kg N ha-1 was applied. Thus, trinexepac-ethyl showed potential to allow hybrids to be fertilized for near maximum yields while minimizing the risk for lodging.