Optimizing Wheat Straw and Grain with Growth Regulators

By Blake Jackson

Farmers in the U.S. Mid-Atlantic region commonly grow winter wheat for both grain and straw, with grain serving as feed and straw used for animal bedding on poultry farms.

To improve grain yields, many producers apply plant growth regulators, which limit vertical growth and reduce the risk of lodging a condition where tall wheat plants fall over, potentially ruining the grain. While the impact of growth regulators on grain yield is well understood, their effect on straw yield and quality remained unclear.

To address this, researchers at Penn State conducted a study to evaluate how a growth regulator, combined with varying nitrogen fertilizer rates, influences both straw yield and quality. The research took place at Penn State’s Russell E. Larson Agricultural Research Center.

“Farmers don’t want their wheat to get so high that it falls over and the grain is ruined, so many have been using plant growth regulators for a long time,” said Daniel Carrijo, assistant professor and extension specialist in grain crop production in the Penn State College of Agricultural Sciences.

“We know that growth regulators can mitigate lodging risk and improve grain yield, but farmers and some of our stakeholders wanted to know their influence on straw yield and quality. This was a very applied project in which we tested a commonly used product called trinexapac-ethyl to determine how it affects straw yield and quality, which also is important on mixed-use farms.”

Over two years, the study tested nine combinations of three nitrogen fertilizer rates and three trinexapac-ethyl treatments. The results showed that trinexapac-ethyl reduced plant height but did not increase stem thickness.

Straw yield declined slightly 8% with two applications and 5% with one but these reductions were not statistically significant. Importantly, the regulator did not affect straw quality or water absorbency, so it remains suitable for bedding. No lodging occurred in any treatment plots, and higher nitrogen rates improved grain protein content.

“Our findings were mixed - we saw that trinexapac-ethyl might slightly reduce straw yield, but it doesn’t harm straw quality or grain yield,” Carrijo said.

“Farmers using trinexapac-ethyl should consider the trade-off: It may help reduce lodging, if that’s a concern, but it might slightly cut straw yield. If straw is a valuable product for a farm, used for bedding, that trade-off could be important.”

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