COVER STORY
Controlling Bermudagrass in Tall Fescue and Zoysiagrass while Reducing Turf Injury By Scott McElroy, Ph.D., Assistant Professor, Turfgrass Weed Science, and Greg Breeden, Research and Extension Associate, Weed Science, University of Tennessee
B
ermudagrass is one of the most difficult-to-control species in turfgrass systems. Its extensive rhizome and stolon system, its aggressive nature and its tolerance to environmental and management stresses are reasons why it is an excellent (and desirable) turfgrass in some situations, as well as why it is difficult to eradicate in situations where it is not wanted. Bermudagrass is problematic in other warm-season grasses, such as zoysiagrass, centipedegrass and St. Augustinegrass, in addition to cool-season grasses, such as tall fescue, Kentucky bluegrass and bentgrass. Bermudagrass is especially problematic in zoysiagrass turf because both species are C-4 warm-season grasses with similar herbicide tolerances.
Previous research on bermudagrass control
In the past, fenoxaprop (Acclaim Extra) and fluazifop (Fusilade II) have been the primary herbicides evaluated for bermudagrass control in tall fescue and zoysiagrass turf. However, injury or quality reduction of tall fescue or zoysiagrass from multiple fenoxaprop or fluazifop applications has been previously reported, decreasing the potential use of these herbicides due to potential phytotoxicity.
Table 1. Active ingredient and product names, along with equivalent active ingredient and product rates utilized in the studies. Herbicide Active Ingredient
Herbicide Product
Active Ingredient Rate1
Product Rate
lb. ai or ae/acre oz./acre fenoxaprop
Acclaim Extra
0.12
28
fluazifop
Fusilade II
0.09
6
fluroxypyr
Spotlight
0.23
20
triclopyr
Turflon Ester
1.00
32
1 Due to differences in herbicide chemistry, fluroxypyr and triclopyr active ingredient rates are presented in acid equivalents per acre, while fenoxaprop and fluazifop are presented as active ingredient per acre. Abbreviations: ai = active ingredient; ae = acid equivalents.
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TENNESSEE TURFGRASS OCTOBER/NOVEMBER 2006
Although triclopyr (Turflon Ester) is an herbicide that is primarily active on broadleaf (dicotyledenous) weeds species, it has also been reported to significantly injure both common and hybrid bermudagrass when applied at twice the labeled rate (4.3 lb./acre). Multiple applications of triclopyr (0.45 lb./a) or triclopyr + clopyralid (0.45 + 0.56 lb./acre) have been reported to injure bermudagrass up to 30%. In fact, injury is so significant that attempts have been made to utilize triclopyr as a selective bermudagrass-control herbicide.
Our research
The goal of our research was to evaluate the use of triclopyr in tank-mix combinations with fluazifop and fenoxaprop for bermudagrass suppression in tall fescue and zoysiagrass turf. In addition, fluroxypyr (Spotlight) was also evaluated in this research because of its similar chemistry to triclopyr and its recent registration for turfgrass use.
Materials and methods
We conducted our research in 2004 and 2005 at the Little Course at Conner Lane (in Franklin, TN) and in 2005 at the West Tennessee Research and Education Center (WTREC) in
Key Research Points at a Glance • Fluazifop (Fusilade II) and fenoxaprop (Acclaim Extra) are two of the most effective products for bermudagrass control in tall fescue and zoysiagrass. • When applied alone for selective bermudagrass control in established turfgrass, fluazifop and fenoxaprop can injure tall fescue and zoysiagrass. • Adding triclopyr (Turflon Ester) safens the use of fluazifop and fenoxaprop, while improving or providing similar bermudagrass control, compared to the same products applied alone.
Email TTA at: tnturfgrassassn@aol.com