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FILLING THE NICHE: The Search for an MSMA Replacement
By Michael Flessner, Graduate Research Assistant, and Scott McElroy, Ph.D., Assistant Professor, Auburn University
M
onosodium methane arsonate, better known as MSMA, faces an uncertain future since the U.S. Environmental Protection Agency (EPA) moved to eliminate all organical arsencial herbicides (organical arsenicals were not eligible for re-registration) in August 2006. While MSMA supporters continue to challenge the EPA restrictions, Auburn University, with support of the Alabama Turfgrass Research Foundation, is conducting research on alternative herbicides. While some currently unlabeled alternatives such as Accent (nicosulfuron) and Discover (clodinafop) could be potential useful as replacements for organical arsenicals, the new options are often more expensive for the turf manager or sod producer, and they typically have a more limited range of weed control.
At the heart of the push to save MSMA is the fact that no good alternatives to MSMA are currently available. New herbicides can control some of the weeds once controlled by MSMA; no herbicide, however, is a complete replacement. The problem is further compounded with the need to find a herbicide that also has adequate turfgrass safety.
We hypothesize that such a replacement could potentially be found by searching for herbicides currently labeled for use in the crop market. Such herbicides, if found effective, could possibly be registered for use in turfgrass and could then be pursued for long-term registration. However, for a herbicide to be deemed a true MSMA replacement,
Table 1. Herbicides Tested. Herbicide
Active Ingredient
Manufacturer
Labeled for use in
Mode of Action
Percent ai in product varies
MSMA
MSMA
many
various
Not well understood
Accent
nicosulfuron
DuPont
Corn
ALS Inhibitor
75%
Discover
Clodinafop
Syngenta
Wheat
ACCase Inhibitor
6.35%
Impact
Topramezone
BASF
Corn
Laudis
Tembotrione
Bayer
Corn
Olympus
Propoxycarbazone
Bayer
Wheat
Carotenoid Biosynthesis Inhibitor Carotenoid Biosynthesis Inhibitor ALS Inhibitor
29.70% 34.5% 70%
Alabama Turf Times >>> S p r i n g 20 09
Table 2. Turfgrass injury and weed control as rated at 4 WAI (2 weeks after second application).**** Herbicide
Rate*
active ingredient (trade name)
lb ai/a (product rate)
Zoysiagrass
Injury** Bermudagrass
Crabgrass
Dallisgrass
Control*** Goosegrass
MSMA (many)
2.025 lb ai/a (2.7 pt/a)
10.0 cd
6.7 c
41.7 b
56.7 a
35.0 b
nicosulfuron (Accent)
0.094 lb ai/a (2 oz/a)
18.3 c
25.0 b
36.7 b
31.7 b
85.0 a
Clodinafop (Discover)
0.063 lb ai/a (16 oz/a)
15.0 c
60.0 a
35.0 b
15.0 c
81.7 a
Topramezone (Impact)
0.016 lb ai/a (0.75 oz/a)
60.0 a
66.7 a
45.0 b
36.7 b
93.3 a
Tembotrione (Laudis)
0.082 lb ai/a (3 oz/a)
36.7 b
73.3 a
60.0 a
48.3 ab
88.3 a
Propoxycarbazone (Olympus)
0.039 lb ai/a (0.9 oz/a)
3.3 de
0.0 c
3.3 c
10.0 c
18.3 c
* Rate denotes rate of herbicide at each of two applications ** Control ratings based on a 0 to 100 scale with 0 equal to no control, 100 equal to complete plant death, and > 80 denotes acceptable control. *** Injury ratings based on a 0 to 100 scale with 0 equal to no injury, 100 equal to complete plant death, < 10 denotes acceptable injury, and > 60 denotes plant necrosis **** Means followed by similar letters are not statistically different
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