Cutting edge: controlling bermudagrass, stabilizing creeper grass colonization

Cutting edge: controlling bermudagrass, stabilizing creeper grass colonization

Multi-year evaluation of bermudagrass control on creeping passes from herbicides and mechanical cutting

Bermudagrass (Cynodon dactylon L. Pers.) is one of the most troublesome weeds of creeping bentgrass (Agrostis stolonifera L.) throughout the transition zone of the United States. Aggressive shaft and rhizome development, combined with bermudagrass tolerance to standard herbicides used for weed control in creeping bermudagrass, increases the potential for bermudagrass invasion. By exploiting winter stress, timely physical damage may lead to increased bermudagrass control. Previous research has reported that tobramizone-based herbicide programs have successfully controlled bermudagrass in cool-season turfgrass.

Our preliminary research showed that fall and winter mechanical cutting reduced bermudagrass stand density while having little effect on creeping bentgrass density. Therefore, additional field trials were conducted at Ballyhack Golf Club, Roanoke, Virginia, from September 2018 to September 2020 to compare tobramizone-based herbicide programs alone or in combination with mechanical chipping to control bermudagrass in a creeping grass fairway. The experiment was in a randomized complete block design with four replications.

Treatments included an untreated control, mechanical chipping, application of tobramzone plus triclopyr at 0.09 and 0.37 ounces a.i. per acre (6.4 and 26 grams a.i. per hectare), respectively, and a combination of mechanical chipping and tobramzone plus triclopyr applied in Same rates. A total of six applications per year of herbicides and cutting were made, with herbicides divided evenly between fall and spring and cutting initiated in the fall and continued at three-week intervals through winter. Final bermudagrass coverage after 2 years of herbicide + cutting was 18%, which represents 75% control and no different than herbicide without cutting. Bermuda grass area under the daily cover progress curve was 40% over the 2-year period compared to 85% in untreated grass. Topramezone plus triclopyr programs significantly increased creeping bentgrass coverage and reduced bermudagrass coverage.

Although cutting significantly reduced bermudagrass cover under herbicide cover alone on a few selected evaluation dates, rapid recovery of bermudagrass reduced its overall effectiveness in these studies.

— Navdeep Godara (ngodara@vt.edu); Shawn D. Askew, Ph.D.; john r. Brewer, Ph.D.; and John N. Peppers, Virginia Tech, Blacksburg, Virginia.

An aerial view of Ghost Creek Golf Course

Colonization stability and efficacy of plant growth-promoting rhizobacteria in creeping weeds

Inoculation with plant growth-promoting rhizobacteria (PGPR) is a new method to improve growth and abiotic stress tolerance of cool-season grasses. Many endogenous PGPR colonize plant roots and produce ACC deaminase, which reduces stress-induced ethylene production, effectively reducing leaf senescence. However, for this symbiosis to have the intended effects on improving stress tolerance, the roots must first be colonized by PGPR using successful and proven inoculation methods. In addition, these methods must be verified under field conditions, which can be difficult due to fluctuating temperatures and humidity, as well as the presence of organisms in the local soil.

In this study, plots of creeping pengrass (Pencross) were inoculated with two new strains of Paraburkholderia aspalathi that showed growth-promoting properties using foliar spray and soil drench inoculation method. Pollination treatments were applied to well-irrigated plots that were subjected to 28 days of deficit irrigation (60% evapotranspiration) followed by 14 days of re-irrigation (100% ET). To evaluate the colonization efficiency of bacteria, roots were sampled from the plots to examine the presence, quantity or density of the bacterial strains that were applied.

The presence of bacterial inoculum in plant tissues was determined by bacterial isolation and quantitative real-time PCR (qPCR) that was designed based on the signature sequence of 16S rDNA in P. aspalathi. Both sequence analysis and bacterial flux from plant tissue were able to confirm that the soil drench method was the most effective inoculation method. Plots inoculated with P. aspalathi using the soil drench method also showed the greatest improvements in drought stress tolerance and post-drought recovery, suggesting that inoculation with these new strains of P. aspalathi using the soil drench method is an effective approach to improve drought stress tolerance and reduce water use. In creeping bentgrass.

— William Erickson (william.errickson@njaes.rutgers.edu), Kashif Jalil and Bingru Huang, Ph.D., Rutgers University, New Brunswick, NJ


Darrell J. Pehr (dpehr@gcsaa.org) is GCM's science editor.

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