Growth regulator offers tradeoffs for winter wheat grown for both grain, straw

UNIVERSITY PARK, Pa. — Growing winter wheat for both grain and straw production is common in poultry farms in the U.S. Mid-Atlantic region, where grain is used for feed and straw is used for animal bedding. Grain yield can be improved by spraying plants with a regulator that halts vertical growth and makes them less prone to falling over, a phenomenon farmers call “lodging” that can greatly reduce grain yields. However, the effect of growth regulators on straw yield and quality was unknown, so a team of researchers at Penn State conducted a study to evaluate the effect of a growth regulator in combination with nitrogen fertilizer applied at different rates. The study was conducted on winter wheat field trials at Penn State’s Russell E. Larson Agricultural Research Center.

The researchers published their findings in Crop, Forage and Turfgrass Management.

“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 Daniela 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 researchers tested nine combinations of three nitrogen fertilizer amounts and three trinexapac-ethyl treatments. They found that trinexapac-ethyl reduced plant height but didn’t increase stem thickness, leading to 8% lower straw yield with two trinexapac-ethyl applications and 5% lower straw yield with a single trinexapac-ethyl application, a difference that was not statistically significant. They found the trinexapac-ethyl didn’t change straw quality or absorbency — meaning it didn’t affect how much water the straw could hold, so it could still be used for animal bedding. The researchers reported that no lodging occurred in any plots and that adding more nitrogen fertilizer resulted in higher 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.”

Larissa Correia, first author on the study, was a visiting scholar in Penn State’s Department of Plant Science. She currently is a research associate at the University of Wisconsin, Madison, Ronald Hoover, senior project associate in the Department of Plant Science, contributed to the research.

The research was funded by Syngenta and the U.S. Department of Agriculture’s National Institute of Food and Agriculture.