WEED CONTROL LESSONS LEARNED IN 2018 By Jim Brosnan, PhD, Greg Breeden, and José J. Vargas
Editor’s note: Tis article was originally published in Tennessee Turfgrass and has been slightly modified for publication in Turf News.
Each year the turfgrass weed science program at the University of Tennessee conducts hundreds of research trials in the field, greenhouse, and laboratory. Despite having an array of different objectives, all of these trials have a singular focus: to help turfgrass managers with weed management issues. Te article below outlines key lessons learned in our program last year that will hopefully be of use to turfgrass managers in the coming season.
Lesson #1 – Explore Weather Data Mother Nature certainly threw sod producers across the southern United States many curveballs in 2018. Te year began with air temperatures measuring much higher than historical averages leading to spring emergence of warm-season turfgrasses (and weeds) occurring earlier than normal. Air temperatures fell in April, measuring nearly 10 degrees cooler (on average) than April 2017. Warming in 2018 (as measured by growing degree day accumulation) was higher than the previous two seasons and this period of warming continued into the fall. Sod producers are encouraged to identify local weather resources in their area for more information about factors potentially affecting production of warm- and cool-season turfgrasses. A detailed breakdown of erratic weather across Tennessee in 2018 is available at:
https://medium.com/@ UTTurfWeeds/several-curveballs-from-mother-nature-in- 2018-d487c9b2015d.
Irregular weather patterns will not only affect the severity of weed infestations in warm- and cool-season turfgrasses
but the efficacy of several herbicide treatments as well. Tat said, local university Extension offices can help. Should sod producers encounter oddities during the 2019 season, they are highly encouraged to contact their local Extension office for a breakdown of climatic conditions that may help explain the situation.
Lesson #2 – Know Your Poa One of the biggest lessons learned last year is that Poa annua populations across the state of Tennessee are very different from one another; and this will likely be true in other regions as well. Tanks to support from the Golf Course Superintendents Association of America (GCSAA) and Tennessee GCSA, our team is currently conducting a survey of Poa annua across the state. Efforts have allowed us to study 72 different populations randomly selected from golf courses during spring 2018 in East, Middle and West Tennessee that had either bermudagrass (Cynodon spp.) or zoysiagrass (Zoysia spp.) as a primary turfgrass species. Tings we’ve learned studying these populations include:
• Poa annua from West Tennessee takes longer to germinate from seed than that found in Middle or East Tennessee. Moreover, populations from West Tennessee grow less vigorously from seed as well.
• Over 64 percent of the Poa annua collected in this survey has some level of resistance to glyphosate (e.g., Roundup)
• Over 58 percent of the Poa annua collected in this survey has some level of resistance to prodiamine (e.g., Barricade)
Herbicide resistant annual bluegrass (Poa annua) infesting a dormant zoysiagrass (Zoysia spp.) turf. 34 TPI Turf News May/June 2019
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