Bermudagrass is most susceptible to injury from root-inhibiting herbicides in spring when soil temperatures are between 50 F and 60 F. This is also the optimal time for preemergence herbicide applications targeting summer annual grasses like crabgrass, which begins germinating around 55 F and increases rapidly as soil temperatures reach 60-70 F. Preemergence applications for goosegrass typically occur slightly later. All of this means that the preemergence application window overlaps with bermudagrass transition from winter overseeding, which creates a trade-off between prioritizing a better transition or suppressing summer weeds.
For decades, many superintendents have successfully managed both bermudagrass transitions and weed pressure using root-inhibiting herbicides such as prodiamine (Barricade), dithiopyr (Dimension), indaziflam (Specticle) and pendimethalin (Pendulum). However, on courses with a history of poor transition, these products may further delay bermudagrass recovery in early summer. In those situations, alternative strategies should be considered.
Bermudagrass tolerance to root-inhibiting herbicides improves as soil temperatures increase. One option is to delay dithiopyr applications until soil temperatures reach 60-65 F, providing early postemergence control of crabgrass and preemergence control of goosegrass. This can be followed by sequential applications of herbicides that do not inhibit root growth like dimethenamid-P (Tower) at 21 fluid ounces of product per acre. Other options include S-metolachlor (Pennant Magnum) and pethoxamid (StriCore), which require multiple applications to achieve extended control. Oxadiazon (Ronstar) remains an excellent and often preferred option, though treated acreage limitations apply under current label restrictions.
Should a weed control program that has historically worked well be adjusted to improve bermudagrass recovery? Weed scientists consistently emphasize that dense, healthy turf is the most effective weed control strategy, and I believe that achieving dense bermudagrass fairways is worth changing up the herbicide regimen. Modifying programs to reduce reliance on root-inhibiting herbicides may be a necessary step to achieving a more successful bermudagrass transition. For more information, reach out to your regional USGA agronomist.
West Region Agronomists:
Brian Whitlark, regional director, West Region – bwhitlark@usga.org
Ross Niewola, agronomist – rniewola@usga.org