ARS | Publication request: PHOTOSYNTHETIC RESPONSES OF 15 RANGE GRASSES TO THE SELECTIVE HERBICIDE SULFOSULFURON

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2003
Publication Date: September 15, 2004
Citation: Monaco, T.A. and J.E. Creech. 2004. Sulfosulfuron effects on growth and photosynthesis of 15 range grasses. Journal of Range Management 57:490-496.

Interpretive Summary: Sulfosulfuron, a selective herbicide was applied to 15 range grasses to determine its photosynthetic impacts. Photosynthesis was most damaged in rhizomatous grasses. Caespitose grasses were less damaged. The reasons for selectivity are unknown, but may be associated with a species ability to metabolize the herbicide making it less harmful to photosynthetic function.

Technical Abstract: There is considerable need to control invasive and undesirable grasses in pastures and rangelands without negatively impacting existing desirable perennial grasses. We conducted a greenhouse experiment to compare photosynthetic and growth responses of 2 invasive annual grasses (cheatgrass = Bromus tectorum L. and medusahead = Taeniatherum caput-medusae (L.) Nevski), 6 caespitose grasses ('Goldar' bluebunch wheatgrass = Pseudoroegneria spicata (Pursh) Love, 'Secar' Snake River wheatgrass = Elymus wawawaiensis J. Carlson & Barkw., 'CD II' crested wheatgrass = Agropyron cristatum (L.) Gaertner x A. desertorum [Fisch. ex Link] Schultes, Sand Hollow big squirreltail germplasm = Elymus multisetus (J.G. Smith) M.E. Jones, basin wildrye = Leymus cinereus (Scribn. & Merr.) Love, and 'Bozoisky' Russian wildrye = Psathyrostachys juncea (Fisch.) Nevski) and 7 rhizomatous grasses ('Rosana' western wheatgrass = Pascopyrum smithii (Rydb.) Love, 'Critana' thickspike wheatgrass = Elymus lanceolatus (Scribn. & Sm.) Gould, 'Greenar' intermediate wheatgrass = Thinopyrum intermedium (Host) Barkw. & Dewey), 'NewHy' wheatgrass = Elymus hoffmannii, beardless wildrye = Leymus triticoides (Buckley) Pilger, quackgrass = Elytrigia repens (L.), and 'Manchar' smooth brome = Bromus inermis Leysser) to the herbicide sulfosulfuron (1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea). Plants of each grass were established in 3-L pots and assigned to the following treatments (n = 4): 1) untreated control, 2) sulfosulfuron low rate (53 g ha-1), and 3) sulfosulfuron high rate (93 g ha-1). In general, 6 of the 7 rhizomatous grasses showed significant (P<0.05) reductions in photosynthetic (i.e., carbon assimilation, stomatal conductance, and leaf transpiration) and growth (shoot dry mass) parameters compared to the control. In contrast, only 1 of the 6 caespitose grasses consistently showed a significant (P<0.05) reduction in photosynthetic and growth parameters. Of the 2 invasive annual grasses, only cheatgrass showed a significant (P<0.05) reduction in both photosynthetic and growth parameters. These results indicate a strong association between herbicide impact, photosynthetic performance, and subsequent reduction in growth. Sulfosulfuron may be an effective management tool to selectively suppress some invasive annual and rhizomatous grasses without adversely affecting desirable grass species.