Turf Talk
CUMYLURON: A New Herbicide for Annual Bluegrass Control in Creeping Bentgrass Putting Greens Scott McElroy, Assistant Professor, Turfgrass Weed Science, Auburn University and Jack Rose, Research Assistant, Turfgrass Weed Science, Auburn University
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umyluron (HM9930) is a new herbicide currently being evaluated for annual bluegrass (Poa annua or simply Poa) control in creeping bentgrass putting greens. Little is known about cumyluron other than what can be gleaned from Internet searches. It is classified as a urea herbicide (http://www.alanwood.net) and is structurally similar to the substituted urea herbicide siduron (Tupersan). This leads one to believe that it is acting on photosystem II similar to other substituted ureas such as diuron. Cumyluron also possible inhibits root development similar to siduron. There are currently limited options for Poa control in creeping bentgrass putting greens (Table 1). Current options are limited to plant growth regulators (PGRs) that behave as slow-acting postemergence herbicides and preemergence control. The PGRs Trimmit (paclobutrazol) and Cutless (flurprimidol) are applied as repeat applications on a 21 to 28 day schedule over one to two years for Poa suppression. Trimmit is the faster and more effective of the two PGRs. One can easily decrease Poa contamination to <5% after four to six applications; however, one must continue to apply Trimmit on a less frequent basis to maintain low Poa levels. Preemergence applications of Bensumec (bensulide) are also utilized for Poa control in creeping bentgrass putting greens. Superintendents are concerned about “root-pruning” and the additional stress this herbicide potentially induces. Regardless of this potential problem, bensumec is the only pre-
emergence herbicides available for Poa control in creeping bentgrass putting greens. Cumyluron has the potential for overcoming the limitation of currently labeled herbicides. First, cumyluron seems to have both preemergence and postemergence activity-thus killing actively growing plants and preventing new from emerging. Second, no negative effects on creeping bentgrass have been observed on initial studies conducted at Auburn University. This is essential to developing a herbicide for an already stressed and sensitive turfgrass management situation.
Research at Grand National Golf Course Materials and Methods: Research was conducted beginning spring 2008 at Grand National Golf Course in Opelika, AL. Research was conducted on a USGA spec creeping bentgrass practice putting green infested with perennial (annual) bluegrass (Poa annua ssp. reptans). The practice green was contaminated with approximately 60% Poa at the time of application. Treatments are listed in Table 2. Cumyluron is thought to be primarily root absorbed; thus irrigation schemes were evaluated to determine if it is advisable to irrigate immediately after application or allow the herbicide to remain on the leaf surface for 24 h before irrigation. Applications were made with a CO2 pressurized sprayer calibrated to deliver approximately 90 gal/A. Results: No injury symptoms were observed on the creeping bentgrass
at any time during the study from 4 March 2008 to 19 March 2009. However, cumyluron at 4.5 fl oz/ 1000 ft2 did reduce overall turfgrass quality in July (Figure 1). Upon closer inspection it appears that the turfgrass quality reduction was due to Poa injury and not creeping bentgrass injury. Superintendent Jeff Oelman referred to these areas as “wilt areas” and he did express a concern regarding the decrease in quality. No turfgrass necrosis or plant death was observed at any time. No changes in Poa composition was observed until late winter-early spring 2009. This was primarily due to the increased growth and seed production of Poa during this time period. Cumyluron at 4.5 fl oz/1000 ft2 controlled Poa the greatest amount (Figure 3; see pictures also). While cumyluron at 1.5 and 3.0 fl oz did decrease Poa numerically; there was no difference in these treatments from the nontreated. No difference was observed between rates when comparing irrigation schemes. Conclusions: Initial results are positive for cumyluron. From these results, it is concluded that two cumyluron applications at 4.5 fl oz/ 1000 ft2 reduce Poa density from approximately 60% to 10 to 20% with little to no disturbance to the playing surface and no injury to the creeping bentgrass putting green. One should consider the Poa density before apply cumyluron, as in densely populated greens Poa control may decrease quality. In such a situation, lower rates over multiple years may be more appropriate.
Table 1. Currently registered products for Poa annua control in creeping bentgrass putting greens.
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PRODUCT
CHEMICAL NAME
CONTROL MODE
RATE- TIMING
LIMITATION
Bensumec
bensulide
Preemergence
2-3 gallons — prior to emergence
Pre only; potential root pruning
Trimmit
paclobutrazol
Postemergence; growth regulation
8 to 16 fl oz/a — 21 to 28 day
Suppression to control
Cutless
fluprimidol
Postemergence; growth regulation
2 to 8 oz wt/a — 14 to 28 day
Suppression only