Primo Changes Plant Hormone Levels That Prompt Beneficial Side Effects For Healthy Turf

Primo (trinexapac-ethyl) is probably the most commonly used plant growth regulator (PGR) on fine turf surfaces throughout the world. Most of us are quite familiar with the fact that, when used at label rates and timings, Primo reduces leaf elongation at four to seven days after initial application and will usually provide a 50 percent reduction in clippings. However, for many turf managers, reduced mowing frequency is often not the primary reason for continued Primo use. What they come to value most are many of the sideor secondary-effects that Primo has on turfgrass growth and development. A recent hypothesis that we were able to test is that increased tillering and prolonged green color of Primotreated leaves may be correlated with increased levels of cytokinins, a group of hormones responsible for cell division, new tiller initiation and delayed senescence. However, before discussing these results, we need to spend some time trying to understand the data and observations on secondary effects that led to this hypothesis. To guide and visualize this discussion, a "Primo roadmap" has been developed presenting primary and secondary effects (Figure 1).