Submitted to: Society for Range Management Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/30/2002
Publication Date: 2/1/2003
Citation: LOUHAICHI, M., RICHMAN, L.M., JOHNSON, D.E., CARPINELLI, M.F. 2003. EFFECT OF OUST® HERBICIDE ON SELECTED RANGELAND FORBS. SOCIETY FOR RANGE MANAGEMENT ANNUAL MEETING. CASPER, WY, FEB. 1-6. PAPER NO. 149.
Interpretive Summary: MEDUSAHEAD IS AN AGGRESSIVE ANNUAL GRASS INTRODUCED FROM EURASIA THAT HAS SPREAD OVER MILLIONS OF ACRES IN THE SEMI-ARID WEST. MEDUSAHEAD FORMS EXCLUSIVE STANDS THAT BURN READILY AND RESIST REESTABLISHMENT OF NATIVE PLANT SPECIES. MEDUSAHEAD INVASION ALSO RESULTS IN ECONOMIC LOSSES TO RURAL COMMUNITIES, AND IT HAS BEEN REPORT THAT MEDUSAHEAD-DOMINATED RANGES HAVE SUFFERED A 40 TO 75% REDUCTION IN GRAZING CAPACITY. A CURRENT STUDY ASSESSED THE EFFECTIVENESS OF THE HERBICIDE SULFOMETURON METHYL ON MEDUSAHEAD AND THE IMPACTS ON ASSOCIATED NATIVE VEGETATION. THE GOAL IS TO CONTROL MEDUSAHEAD WHILE MAINTAINING NATIVE PLANT COMMUNITIES. THE HERBICIDE TREATMENT CONTROLLED MEDUSAHEAD, BUT REDUCED THE DENSITY OF SEVEN OF THE ELEVEN NATIVE PLANT SPECIES TESTED. tHE DENSITY OF FOUR OTHER SPECIES WERE NOT AFFECTED BY THE HERBICIDE TREATMENT. MORE RESEARCH IS NEEDED TO IDENTIFY OPTIMAL HERBICIDE APPLICATION RATES TO THAT MEDUSAHEAD CAN BE CONTROLLED WITHOUT NEGATIVELY IMPACTING NATIVE PLANT SPECIES.
Technical Abstract: Medusahead (Taeniatherum caput-medusae [L.] Nevski), a non-native, winter-annual grass, invades rangelands and threatens biotic diversity. Oust (sulfometuron methyl) has been used to control medusahead. Oust interferes with enzymes (acetohydroxy acid synthase [AHS] that are necessary for plant cell division. Pre-emergence treatments control weeds through root uptake. We assessed the impacts of fall applications (pre-emergent) of Oust on native forbs on the sagebrush/bunchgrass steppe of central Oregon. We evaluated the population dynamics of selected native plant species on plots that have been treated with Oust and on untreated controls. The experimental design was a split-plot in time (repeated measures) with randomly applied treatments. To ensure that native plant populations were similar across treatments and controls, we employed plot pairing with pairs having similar initial species composition, density, and vigor of native plants. The application rate was 70.0 g ai/ha (1.0 oz. Ai/acre). Seven of eleven native forbs tested had a significant reduction in density (P 0.10): Trifolium macrocephalum (Pursh.) Poir., Lupinus saxosus T. J. Howell, Balsamorhiza serrata A. Nels. & J. F. Macbr., Crepis intermedia Gray, Phlox longifolia Nutt., Allium acuminatum Hook., and Agoseris glauca (Pursh.) Raf. Further research is needed to allow for control of medusahead without negatively impacting native plant species.