Efficacy of ‘Tenacity’ in Late Spring to Eliminate Poa annua in Kentucky Bluegrass Fairways

W.J. Johnston, PhD and C.T. Golob, MS Crop and Soil Sciences, Washington State University, Pullman, WA

You can download this article as a pdf file at this very bottom of this post.

Kentucky bluegrass (Poa pratensis L.) golf course fairway infested with annual bluegrass (Poa annua L.) can be unattractive, hard to manage, and have reduced playability during much of the golf season.  Although not currently registered for use in Canada, we thought it might be of interest to Canadian turfgrass managers to review our effort in the USA to control annual bluegrass in Kentucky bluegrass fairways. 

OBJECTIVE

Determine the efficacy of Tenacity 4SC combined with several herbicides to eliminate Poa annua from Kentucky bluegrass fairways.

MATERIALS & METHODS

Research was conducted on a Kentucky bluegrass fairway infested with P. annua at the Palouse Ridge Golf Club at Washington State University in Pullman, WA.  Treatments were: Tenacity 5 fl oz/A + Xonerate 2 oz/A, Tenacity 4 fl oz/A + Xonerate 1 oz/A, Tenacity 5 fl oz/A + Turflon 16 fl oz/A, 19660A 1 fl oz/A + Turflon 16 fl oz/A, Tenacity 5 fl oz/A + Trimmit 16 fl oz/A, and Tenacity 5 fl oz/A + Trimmit 16 fl oz/A + Turflon 16 fl oz/A.  Initial treatments were made on May 2, 2013 followed by repeat applications on May 23, and June 13, 2013.  Applications in 2014 are currently being evaluated in a spring/spring program (only 2013 data presented).

RESULTS

Tenacity 5 fl oz/A + Xonerate 2 oz/A and Tenacity 4 fl oz/A + Xonerate 1 oz/A resulted in the greatest reduction of P. annua, 86 and 82%, respectively, compared to the controls (Fig. 1).  However, associated with the Tenacity 5 fl oz/A + Xonerate 2 oz/A treatment was a high level of P. annua phytotoxicity and at times an unacceptable phytotoxicity on Kentucky bluegrass (Fig. 2).  In addition, open, depressed areas in the fairway where the P. annua had died presented undesirable playing conditions during peak summer play.  It was not till the early fall that the Kentucky bluegrass aggressively began to fill these depressions and a noticeable shift in the fairway population toward Kentucky bluegrass was evident (Fig. 3 and 4).  Tenacity 4 fl oz/A + Xonerate 1 oz/A also resulted in a high level of P. annua phytotoxicity for several weeks, but at a lower level of Kentucky bluegrass phytotoxicity and did not cause P. annua to quickly disappear creating open areas and depressions in the fairway.

CONCLUSIONS

Tenacity 4 fl oz/A + Xonerate 1 oz/A may be the most desirable P. annua control option to consider in terms of seasonal playability.  Complete P. annua control was not achieved with any treatment; therefore, a multi-year program may be needed to achieve this goal.   

  Fig. 1.  Percent change in Poa annua in a Kentucky bluegrass fairway 6, 12, and 18 weeks after initial treatment. (see pdf for figures)

  Fig. 2.  Kentucky bluegrass phytotoxicity following application on May 2 + May 23 + June 13, 2013. (see pdf for figures)  

Fig. 3. Tenacity combined with other herbicides to control Poa annua 18 WAIT on a Kentucky bluegrass fairway.

Fig. 4. Tenacity combined with other herbicides to control Poa annua 18 WAIT on a Kentucky bluegrass fairway.