Rehabilitating Downy Brome (Bromus tectorum)–Invaded Shrublands Using Imazapic and Seeding with Native Shrubs

Abstract

Rehabilitation of downy brome–infested shrublands is challenging once this invasive grass dominates native communities. The effectiveness of imazapic herbicide in reducing downy brome cover has been variable, and there is uncertainty about the impacts of imazapic on native species. We used a before-after-control-impact (BACI) field experiment and greenhouse studies to (1) determine if imazapic herbicide applied at 132 g ai ha−1 (8 oz/ac−1) and seeding with two native shrub species (Wyoming big sagebrush [Artemisia tridentata] and Mexican cliffrose [Purshia mexicana]) reduced downy brome cover and promoted shrub establishment, (2) assess potential effects of imazapic on nontarget plant species and plant community composition, and (3) determine if imazapic affected downy brome or seeded shrub species when applied at different developmental stages. Seeding shrubs, alone, or in combination with imazapic application, did not significantly increase shrub density, possibly because of droughty conditions. In the field, imazapic reduced downy brome cover by 20% and nontarget forb cover by 25% and altered plant community composition the first year after treatment. Imazapic was lethal to downy brome at all growth stages in the greenhouse and reduced shrub germination by 50 to 80%, but older shrub seedlings were more tolerant of the herbicide. We conclude that a one-time application of imazapic combined with seeding shrubs was only slightly effective in rehabilitating areas with high downy brome and thatch cover and resulted in short-term impacts to nontarget species. These results highlight the need to treat downy brome infestations before they become too large. Also, removing thatch prior to treating with imazapic, although likely lethal to the native shrubs we studied, could increase the effectiveness of imazapic.

Downy Brome (Bromus tectorum) Control with Imazapic on Montana Grasslands

“…The most noteworthy exception to that was in the POST treatment, where 70 g ai ha 21 resulted in lower control than did the other rates. Our results are consistent with label recommendations of 105 to 211 g ai ha 21 (Anonymous 2008) and those from other studies (Baker et al 2009;Davison and Smith 2007;Elseroad and Rudd 2011;Owen et al 2011). Downy brome control may increase with increasing imazapic application rate (Morris et al 2009), but high rates can also increase the risk of injury to Figure 1.…”

“…In reviewing the literature, we found one study that addressed downy brome growth stage at the time of imazapic application. In this greenhouse study, imazapic was applied at 132 g ai ha 21 to downy brome seeds, to plants with two to four leaves, and to plants with 5 to 10 leaves (Owen et al 2011). Downy brome mortality was 90 and 100% after imazapic treatment, regardless of timing of application; however, results from the greenhouse study contradicted results from a companion field study where growth stage was not reported (Owen et al 2011).…”

“…In this greenhouse study, imazapic was applied at 132 g ai ha 21 to downy brome seeds, to plants with two to four leaves, and to plants with 5 to 10 leaves (Owen et al 2011). Downy brome mortality was 90 and 100% after imazapic treatment, regardless of timing of application; however, results from the greenhouse study contradicted results from a companion field study where growth stage was not reported (Owen et al 2011). Because our data indicate that timing of imazapic application influences its efficacy, we believe researchers and land managers should be aware of the growth stage of downy brome when imazapic applications are made and interpret results with that factor in mind.…”

Using revegetation to suppress invasive plants in grasslands and forests

“…Of those five, two found at least mixed support for woody revegetation suppressing IPS. Cabin, Weller, Lorence, Cordell, and Hadway () found planting and seeding native Hawai'ian woody species increased understorey cover and reduced invasion of the grass Pennisetum setaceum (Fountain grass), whereas Owen, Sieg, and Gehring () found seeding native shrubs to be ineffective at suppressing the grass Bromus tectorum (Cheatgrass). Notably, Knutson et al.…”

Imazapic Activity in a Semiarid Climate in Downy Brome (Bromus tectorum)–Infested Rangeland and CRP Sites

“…However, other studies from semiarid climates resulted in only 1 yr of control over downy brome and other invasive annual grasses. For example, Owen et al (2011) reported that imazapic applied at 132 g ha À1 in the late fall reduced downy brome cover and biomass during the first season after application but had no effect during the second season. Similarly, Sheley et al (2007) found that medusahead [Taeniatherum caput-medusae (L.) Nevski] in eastern Oregon was effectively controlled by imazapic (!…”