There have been many talks about different herbicide-resistant strands of Poa annua in warm-season turf over the last few years. This has been primarily further south of our region. However, I have seen what we believe was resistance in Louisville, Ky. This case was not confirmed, but all indications pointed to resistant strands.
For the most part, the resistance is to prodiamine and glysophate used in the spring as a pre-emergent and in clean up applications. We are not blowing the whistle and saying that everyone has resistant strands, but we want everyone to be aware and take the proper precautions in moving forward.
The most important aspect of this resistance is a rotation of herbicides. A rotation of Prodiamine, Dithiopyr, and Oxidiazon, among others, is the best course of action for pre-emergent. While prodiamine use has been the most common because of its lower cost, the cost in the future when resistance is greater may cost more in the long run. The rotation of these herbicides should begin before you start to see the resistance. According to Patrick McCullough, Ph.D., in an article in Golfdom from January 2016, dithiopyr is not effective in controlling Poa in population with known resistance to prodiamine. By starting your rotation now, you not only stop resistance to one but two, good-quality, cost-effective pre-emergents.
As well as pre-emergent resistance, selective and non-selective post-emergent herbicides should be rotated as well. The most common of these is glysophate. Glysophate is the most cost-effective herbicide to use, however a rotation with sulfonylureas will help lessen this issue.
While additional budget dollars may be required to change these applications, you can always put your areas of use on a rotation as well. Instead of eliminating glysophate, rotate half or a third of your warm season turf each year. This will take less immediate budget dollars and begins a good resistance management program.
Thanks again as always!
