This time of year is usually a welcome relief for many in the golf industry. Turning the calendar to October may mean different things for different people but I hope you find some extra time to focus on things away from the golf course now that summer has passed. With that said, there are still a few things to keep a close eye on as fall sets in, especially soil temperatures. Soil temperatures dictate the activity of many pests, including weeds and diseases. Amongst these challenges are two of the most important for bermudagrass managers in the Southeast: Poa annua and spring dead spot.
Whether you monitor soil temperatures with a thermometer or use a soil temperature map, I hope you are paying attention because many in the Southeast are close to some critical windows. A soil temperature of 70 F at a 2-inch depth is a good trigger for preventative fungicide applications for spring dead spot and preemergence herbicide applications for Poa annua control. Here’s what the research shows:
Poa annua germinates when soil temperatures drop below 67 F for five consecutive days with adequate soil moisture (Taylor et al., 2021). To be effective, preemergence herbicide applications must begin before these conditions are present. Successful control will likely require a combination of cultural practices along with pre and postemergence applications.
The causal pathogen of spring dead spot, Ophiosphaerella spp., is best controlled with fungicide applications made in the fall when soil temperatures are between 70 F and 55 F (Hutchens, 2022). These applications need to be watered in. SDHI and DMI fungicides have provided the best control.
Timing is just one factor in managing spring dead spot or Poa annua. Pesticide selection, rate and application method, soil conditions, equipment calibration and post-application irrigation all play critical roles in effective control. Furthermore, tolerance or resistance to control products can throw a significant curveball into management programs. Research into these pests is ongoing and routinely provides superintendents with new information and improved control methods. In fact, the Resist Poa research team recently published a paper on developing and implementing a sustainable integrated weed management program for herbicide-resistant Poa annua in turfgrass. No matter your pest, nailing your application timing based on soil temperatures will be critical to success.
References
Hutchens, W. J. (2022). Biology, Epidemiology, and Management of Spring Dead Spot of Bermudagrass [Doctoral dissertation, Virginia Polytechnic Institute and University]. Virginia Tech University Libraries.
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
Chris Neff, agronomist – cneff@usga.org