Biological Control of Poa annua in Fairways

Note:  This is an abbreviated report.  The complete 2017 NTA Research Report with figures, application dates, etc. is available at (Research – Pullman; Biological Control of Poa annua in Fairways)

William Johnston and Charles Golob

Department of Crop and Soils Sciences, Washington State University

Project Background:  

Elimination of P. annua from golf course turf has been an objective of turfgrass managers and research personnel for decades.  Its elimination from golf course fairways will enhance aesthetics, playability, save money and labor, and make the game a more positive experience for golfers.  The use of a biological control to achieve this objective will be proactive environmental stewardship by the turfgrass industry.

Showing promise and warranting additional research is Pseudomonas fluorescens strain D7, a deleterious rhizosphere bacteria that has been registered (EPA Reg No. 71975-U, 71975-WA-001) by Verdesian Life Sciences primarily as a biological control (herbicide) in the agricultural sector for the control of downy brome, aka cheatgrass (Bromus tectorum).  D7 shows promise to provide biological control of weeds in the PNW, it was developed at WSU, has been under ongoing WSU research for over 20 years, and has been tested on numerous soils in the PNW.  Anecdotal observations have indicated that D7 might have some control of annual bluegrass.  However, research is needed to confirm, or dispute, the potential of D7 for the control of P. annua in turf.  

Uniqueness of the study:

1. Potentially identify a biological control of P. annua.
2. A single application may provide long-term control.
3. Biological control may eliminate P. annua seed presently in the seed bank over time, which is not possible with currently available herbicides.

Research Objectives:

1) Golf course study to determine the effect of timing and rates of D7 (fall only vs. fall + spring) on P. annua control in a mix P. annua/Kentucky bluegrass fairway over several years.
2) Fairway study to determine the effect of herbicide treatments (Tenacity + Xonerate and PoaCure) to initially knock down the P. annua population followed by D7 applications for long-term control. 
3) Evaluation of P. fluorescens strains, other than D7, to control P. annua.   

Experimental Design & Methods:

Study 1 - evaluate timing and rates of D7 (D7 applied only in year 1 for P. annua control over 3 years.  Field studies were initiated at Palouse Ridge Golf Course in late fall 2015 with applications of D7 to a Kentucky bluegrass/P. annua fairway.  

D7 applied fall only.  D7, 3 applications, was applied fall 2015 at 0, 2, 10, or 30 g/acre.  PoaCure was also applied at 1.26 fl oz/1000 ft2 for a chemical treatment for comparison fall 2015.  Three applications of PoaCure were made fall 2017.  Plots were evaluated for P. annua control and turfgrass quality during 2016 and 2017.

D7 applied fall + spring.  D7 was applied, 1 application, fall 2015 and spring 2016.  PoaCure was applied fall 2015, 1 application, and spring 2016, 3 applications.  Three applications of PoaCure were made spring 2017 and 3 applications of PoaCure were made fall 2017.  Plots were evaluated for P. annua control and turfgrass quality during 2016 and 2017.

Study 2 – Chemical + Biological study to evaluate applications of herbicides (to initially knock back the P. annua population) followed by D7 applications over the top of the initial herbicide treatments.  Herbicide treatments were: 1) PoaCure at 1.26 fl oz/1000 ft2 in 3 applications spring 2016, 3 applications fall 2016, and 3 applications summer 2017.  2) Tenacity (4 fl oz/1000 ft2) + Xonerate (1.4 fl oz/1000 ft2) in 3 applications fall 2016 and 3 applications summer 2017.  D7 was applied at 2, 10, or 30 g/acre fall 2016 and 1, 5, or 15 fl oz/A fall 2017; note, change in D7 formulation but equivalent rates.  Plots were evaluated for P. annua control, turfgrass quality, etc. during 2016 and 2017.

Study 3 (new objective) – evaluation of P. fluorescens strains (other than D7) to selectively control P. annua.  A combination of three P. fluorescens strains reported to have selective control of P. annua were applied to a fairway and a green at the Palouse Ridge Golf Course at WSU on 11/2/17.  Also, currently underway are growth chamber and greenhouse studies evaluating formulations and rates on germination and growth of 6 turfgrass species.  


2016 (Year 1) – see 2016 Biological Control of Poa annua in Fairways at

2017 (Year 2)   

Study 1.  D7 applied fall 2015 only.  

On the final 2017 rating date, 2 years after the initial application of D7, there was no statistical differences in P. annua control by any D7 treatment.  Kennedy, Hansen, and Stubbs had observed approximately a 50% reduction in cheatgrass, a cool-season grass with a growth habit similar to P. annua, 2 years following an application of D7.  To date we have seen little evidence of P. annua control with a single fall only application of D7; however, we will continue to monitor these plots in 2018.  

PoaCure numerically showed 4% less P. annua than the check, which indicates that the P. annua population was at least not increasing, as is the usual case.  Three fall 2017 applications of PoaCure made were after the 9/15/17 rating date; thus, any control will not be evident till 2018.  

Study 1.  D7 applied fall 2015 + spring 2016.

Applying D7 in both the fall 2015 and the spring 2016 did not improve the control of P. annua.  There was no statistical difference between any of the D7 treatments and the check.  

PoaCure numerically showed 11% less P. annua than the check, which was better P. annua control than noted above in the fall 2015 only study.  Johnston and Golob (2015) have noted that spring applications of PoaCure, which these plots received in 2016 and 2017, in the Pacific Northwest have not provided the significant control of P. annua seen with fall applications.  Three fall 2017 applications of PoaCure made in 2017 were after the 9/15/17 rating date and thus any control will not be evident till 2018.  

Study 2.  Chemical + Biocontrol.  

Unlike study 1, the reduction in P. annua compared to the check by both Tenacity + Xonerate and PoaCure treatments was evident.  Compared to the 5/26/16 rating (36% P. annua) by fall 2017 P. annua in the check had increased to 56% while P. annua in the Tenacity + Xonerate plots had decreased to 17% and the PoaCure plots had a decrease to 22%.  Thus, a reduction in P. annua was accomplished with chemical treatments.  

D7 was applied in late fall 2016 and 2017.  Although there were no D7 alone treatments in the study, based on results from study 1, to date there does not appear to be additional control of P. annua by D7.  

As anticipated, based on previous research (Golob and Johnston, 2015), the decrease in turfgrass quality due to the Tenacity + Xonerate application in fall 2016 and summer 2017 was completely gone by 9/15/17.  Tenacity + Xonerate and PoaCure treatments had turfgrass quality ratings significantly better than the check.  

Study 3.  (new objective)  Evaluation of additional strains of P. fluorescens.  Field and laboratory studies were initiated late 2017.  Field evaluation, on a green and fairway at Palouse Ridge Golf Course, of treatments applied fall 2017 will begin spring 2018.


Golob, C.T., and W.J. Johnston.  2015.  Tenacity 4SC and Xonerate 70WDG in a spring-summer program for selective Poa annua control (post-emergence) in Kentucky bluegrass fairways.  2015 Washington State Weed Conference.  Wenatchee, WA.

Kennedy, A.C.  2016.  Pseudomonas fluorescens strains selectively suppress annual bluegrass (Poa annua L.).  Biological Control 103:210-217.

Kennedy, A.C., B.N. Johnson, and T.L. Stubbs.  2001.  Host range of a deleterious rhizobacterium for biological control of downy brome.  Weed Sci. 49(6):792-797.

Kennedy, A.C., T.L. Stubbs, and J.C. Hansen.  2011.  Microbial control of cheatgrass, jointed goatrass, and medusahead. p_kennedy.ann.pdf.

Verdesian Life Sciences.  2016.  Verdesian Life Sciences announces new biological herbicide.