January 12, 2015

Mowing, mulching and seeding to control false-brome on the Eugene District, BLM, Oregon

Matt Blakeley-Smith and Thomas N. Kaye | 2008

False-brome (Brachypodium sylvaticum) is an invasive perennial grass which is quickly spreading through the Pacific Northwest. Naturalized populations of False-brome have been observed in the Willamette Valley as early as

False-brome (Brachypodium sylvaticum) is an invasive perennial grass which is quickly spreading through the Pacific Northwest. Naturalized populations of False-brome have been observed in the Willamette Valley as early as the 1960’s. Recently, new populations have been observed in Washington and California. It is capable of completely dominating understory and open habitats to the exclusion of most other native species and its palatability to wildlife is very low. It appears to inhibit tree seedling establishment and may displace endangered species, such as Kincaid’s lupine as well as the threatened roadside plant, wayside aster. This species establishes in disturbed habitats as vehicles and equipment spread the seed to new areas. Since road systems are frequently disturbed, they serve both as a source of seed dispersal as well as likely locations for the establishment of new populations.

The purpose of this project is to develop effective non-herbicide control methods for false-brome, with an emphasis on reducing spread of the species along roadways via seed dispersal. We developed one experiment that evaluated the effectiveness of mowing, mulching, and seeding with native grasses to control false-brome. A second experiment assessed the window of opportunity for mowing false-brome. Results from these experiments may be used by land managers to reduce false-brome abundance along roadways and allow for the reestablishment of native plant communities. Invasive species control and revegetation is intertwined with controlling surface erosion, sedimentation, and roadside stabilization.

We asked four specific research questions:

  1. How well do different types of mulches inhibit regrowth of false-brome?
  2. How long does a single treatment last, or how frequently do treatments need to be reapplied?
  3. Are the mulching and seeding treatments effective at establishing native blue wildrye (Elymus glaucus) and Columbia brome (Bromus vulgaris) as a competitive bio-barrier to false-brome?
  4. Over what time period can false-brome be mowed to achieve effective reduction in false-brome seed production?

Our first experiment, concerning the efficacy of our three types of mulching took place in 2007. Our second experiment which aimed to determine the most effective mowing window, took place in 2008. Through these two years we were able to create preliminary results to each of our four research questions.

  1. Our three mulch types, cottonwood, Douglas-fir, and blue wildrye all were able to significantly reduce brome cover as compared to control and mow-only plots. Blue wildrye was seen to be most effective, yet the difference between all three mulches was not seen to be statistically significant.
  2. Our findings thus far indicate that mowing once during the month of June can fully eliminate seed production for one season. Mowing once and mulching can result in two years of seed suppression, with an average of less than 5 flowering stems per plot (0.5 m2). Plots that were mowed but not mulched quickly recovered after one year, but did afford one year of seed control. We must continue to monitor the treatment plots for a number of years in order to fully understand the recovery of the mulch plots.
  3. There was a significant difference in percent cover of established grasses one year following seeding. The seeded grasses did not flower in 2008 so we were not able to distinguish between the two species seeded. The cover values reported are therefore a sum of the two species. There was a significant difference in grass establishment between the control plots and the three mulch plots. Control plots had an average of 0.5% cover while the three mulch treatments each had average covers of at least 3.4% and as high as 4.5%. However, establishment of native grasses was so low that it is unlikely that there will be sufficient biomass to form the “bio-barrier” that we hoped for. An effective competitor would require a minimum of 50% cover, with values in the 90’s being preferable for true false-brome suppression.
  4. In 2008 Mowing took place over the end of May though the month of June, and into the beginning of July. BLM plots that were mowed on May 21st, 2008 re-sprouted and were not significantly different from controls in the number of false-brome flowering stems following mowing. The plots that were mowed on June 3rd, June 16th, and July 8th, 2008 were unable to re-sprout and had significantly less false-brome flowering stems than the controls. The findings from these two experiments suggest that mowing false-brome anytime during the month of June can result in near elimination of seed production for the entire growing season. Despite the fact that the best control was attained on July 6th and 8th, we recommend taking a conservative approach by avoiding mowing in July since site to site variability could result in the production of viable seed by some early flowering individuals. Mowing false-brome after seed production would have disastrous consequences, since the seed would be distributed over the entire area mowed. Our findings also indicate that false-brome re-sprouts and will produce viable seed if mowing occurs too early in the season.