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ARS Home » Pacific West Area » Burns, Oregon » Range and Meadow Forage Management Research » Research » Publications at this Location » Publication #292488
Title: Effects of integrating mowing and imazapyr application on African rue (Peganum harmala) and native perennial grasses

Author
item JOHNSON, DUSTIN - Oregon State University
item Davies, Kirk

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2013
Publication Date: 1/28/2015
Publication URL: http://handle.nal.usda.gov/10113/60297
Citation: Johnson, D.D., Davies, K.W. 2015. Effects of integrating mowing and imazapyr application on African rue (Peganum harmala) and native perennial grasses. Invasive Plant Science and Management. 7(4):617-623. doi: 10.1614/IPSM-D-13-00019.1.

Interpretive Summary: African rue is a poisonous perennial forb that readily invades salt desert shrub and sagebrush rangelands. Information on effective control of African rue with minimal non-target damage to native perennial grasses in sagebrush rangelands is limited. We evaluated the effects of three application rates of imazapyr with and without a mowing treatment on African rue and native perennial grasses at five sites in eastern Oregon. Imazapyr resulted in significant reductions in African rue, regardless of application rate or mowing treatment. Mowing had no effect on African rue or perennial grasses. Higher rates of imazapyr resulted in significant reductions in perennial grasses, whereas the low rate had minimal effect on perennial grasses. Our results suggest that the recommended rate for controlling African rue (0.85 kg a.i. · ha-1) could be cut to a third on sites similar to those include in this study without reducing the effectiveness of the treatment.

Technical Abstract: African rue (Peganum harmala L.) is a poisonous perennial forb that readily invades salt desert shrub and sagebrush steppe rangelands. Information detailing options for integrated management of African rue are lacking. To date, a limited number of studies have researched the efficacy of different herbicides for controlling African rue, but none have investigated integrated approaches to its management. We broadcast applied three rates (0.275 kg a.i. · ha-1, 0.55 kg a.i. · ha-1, and 0.85 kg a.i. · ha-1) of imazapyr with and without a mowing treatment to five sites in eastern Oregon when African rue was in full bloom. Imazapyr resulted in significant reductions in both the cover and density of African rue, regardless of application rate or mowing treatment (P < 0.05). Mowing had no effect on African rue cover or density (P > 0.05). Higher rates of imazapyr resulted in significant reductions in the cover of native perennial bunchgrasses (P < 0.05), whereas the low rate did not affect perennial grass cover, regardless of mowing treatment (P > 0.05). Applications of imazapyr generally reduced the density of perennial bunchgrasses. Integrating a mowing treatment with imazapyr applications was less effective for controlling African rue than applying herbicide alone. Mowing prior to imazapyr also did not increase survival of perennial grasses. Integrating repeated and/or earlier mowing treatments with imazapyr may have provided better results. Our results suggest that the recommended rate for controlling African rue (0.85 kg a.i. · ha-1) could be cut to a third on dry flood plain ecological sites without comprising the effectiveness of imazapyr for controlling African rue. This lower rate would reduce non-target damage to native perennial grasses which are the dominant functional group in the herbaceous understory. Less damage to native perennial grasses would probably accelerate understory recovery and also help prevent other exotic species for increasing when African rue is controlled.