Plant Growth Regulator Considerations for Winter Small Grains
The Jointing Stage
Some wheat fields in southern PA are already at the Feekes 6 stage also known as jointing. This stage marks the end of tillering and the beginning of the stem elongation phase. It is characterized by the first node of the stem being visible at the base of the shoot (Figure 1). This stage coincides with the initial window for some growth regulators (PGR) including Palisade EC (trinexapac-ethyl). PGRs can be applied to small grains to decrease plant height and reduce the risk of plant lodging.
Figure 1. Wheat plant at stage Feekes 6. Source: University of Wisconsin, Madison.
Effect of Palisade EC on plant height
Results from a study we conducted in Centre County in the 2022-2023 and 2023-2024 growing seasons showed that the application of Palisade EC at 14 oz/ac decreased wheat plant height by 3-10%, depending on the year and mode of application. This is on par with other studies, which have also reported modest but consistent reductions in wheat plant height with Palisade EC.
Effect of Palisade EC on grain and straw yield
In the absence of lodging, the application of Palisade EC will not hurt or increase grain yield. Therefore, if lodging is a concern, making an application now can be a good strategy to protect the crop against future wind damage. However, it is important to keep in mind that if lodging does not occur, the application would have been in vain, so one must weigh the risks according to their situation (and a bit of luck in predicting the weather). Another consideration is the effect of Palisade EC on wheat straw. Our research showed that when lodging did not occur, while Palisade EC did not decrease grain yield, in some situations, it decreased straw yield by up to 8%. This was caused by Palisade EC making the plants shorter but not thicker. In other words, stem length was reduced and stem diameter remained the same, resulting in lower straw biomass. This is a consideration for producers who rely on wheat straw for animal bedding and other end uses.
