To say that the spring of 2023 has been frustrating would be an understatement. The sporadic temperature swings we experienced throughout the winter have continued into spring and have made Poa annua control a real challenge for many golf courses in the Southeast. A month ago, I wrote that golf courses were slowly “Ramping Up” and golfers and maintenance teams both needed to be patient while we wait for warmer weather to arrive. Unfortunately, not much has changed since then. Soil temperatures are just starting to rise in many areas and turfgrasses are just starting to begin active growth. Bentgrass greens are still recovering from spring aeration and winter weeds are still thriving.
I have seen Poa annua on every warm-season golf course I have been to this year. Many factors contributed to the abundance of Poa annua, including:
- Prolonged weather that favored Poa annua germination and growth. Research from the University of Tennessee shows that Poa annua germinates when soil temperatures are below 67 degrees F for seven consecutive days with at least 0.5 inch of rainfall (Taylor et al., 2021).
- The same soil temperatures that are ideal for Poa annua are not optimal for warm-season turfgrass growth. These grasses grow best when air temperatures are between 80 and 95 degrees F. There has been a prolonged period of time since last October where Poa annua has been germinating and thriving while warm-season turfgrass growth was slow or inactive.
- An increase in traffic at most golf courses creates thin turfgrass with poor density – perfect for Poa annua germination.
- Herbicide resistance means many herbicide modes of action no longer provide acceptable control of Poa annua. Rotating chemistries and using sound application methods can prevent or delay the onset of resistance.
Poa annua will naturally be less prevalent as temperatures increase and warm-season turfgrasses begin to grow. I would wait to make postemergence applications until warm-season turfgrasses are actively growing and air temperatures are consistently above 75 degrees F. If you want a deeper dive into Poa annua, I recommend the research paper “Current Understanding of the Poa annua Life Cycle.” To learn more about resistance management or screening for resistance, visit the website of the USDA-SCRI Annual Bluegrass Collective at Resist Poa, or reach out to your regional USGA agronomist.
Reference
Taylor, D.R., Prorock, M., Horvath, B.J., Brosnan, J.T. (2021). Modeling seasonal emergence of Poa annua in urban greenspace. Scientific Reports, 11(1), 18960.
Southeast Region Agronomists:
Chris Hartwiger, director, Agronomy – chartwiger@usga.org
Jordan Booth, Ph.D., director, USGA Course Consulting Service – jbooth@usga.org
John Rowland, Ph.D., agronomist – jrowland@usga.org