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

Abstract

Downy brome is a problematic invasive annual grass throughout western rangeland and has been increasing its abundance, spread, and impacts across Montana during the past several years. In an effort to develop effective management recommendations for control of downy brome on Montana rangeland, we compiled data from 24 trials across the state that investigated efficacy of imazapic (Plateau®, BASF Corporation, Research Triangle Park, NC) applied at various rates and timings and with methylated seed oil (MSO) or a nonionic surfactant (NIS). We ran a mixed-model ANOVA to test for main effects and interactions across application rate (70, 105, 141, 176, and 211 g ai ha−1), application timing (preemergent [PRE], early postemergent [EPOST, one- to two-leaf growth stage], and postemergent [POST, three- to four-leaf growth stage]), and adjuvant (MSO, NIS). Application timing and rate interacted to affect downy brome control (P = 0.0033). PRE imazapic application resulted in the lowest downy brome control (5 to 19%), followed by POST application (25 to 77%) and EPOST application (70 to 95%). Downy brome control remained fairly consistent across rates within application timing. Adjuvant (MSO or NIS) did not affect downy brome control (P = 0.2789). Our data indicate that POST application at 105 to 141 g ai ha−1 provides the most-consistent, short-term control of downy brome. Furthermore, applying imazapic to downy brome seedlings shortly after emergence (one- to two-leaf growth stage) provided better control than applying it to older downy brome seedlings (three- to four-leaf growth stage).

Indaziflam: a new cellulose‐biosynthesis‐inhibiting herbicide provides long‐term control of invasive winter annual grasses

“…Currently, there has been one downy brome biotype identified that is highly resistant to acetolactate synthase (ALS) (imazamox, primisulfuron, propoxycarbazone, sulfosulfuron) and photosystem II inhibitors (PSII) (atrazine, metribuzin) and moderately resistant to acetyl CoA carboxylase inhibitors (ACCase) (clethodim, fluazifop) . Imazapic and glyphosate are currently the two most commonly recommended herbicides for invasive winter annual grass control; however, these herbicides provide inconsistent control, and represent two modes of action that are prone to resistance development . New modes of action for resistance management, such as CBIs, will be increasingly important for controlling downy brome and other invasive winter annual grasses in non‐crop areas.…”

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

“…Downy brome control with imazapic is somewhat inconsistent (Mangold et al 2013); based on our findings, we conclude that this inconsistency cannot be explained by its degradation rate in the soil. Both our field observations and results from the greenhouse bioassay indicate that when imazapic is applied PRE or POST in the fall, it persists to provide control of downy brome seeds that germinate and emerge the following spring.…”

“…Chemical control of downy brome on rangelands in the West has focused primarily on imazapic, an acetolacetate synthase inhibitor and member of the imidazolinone herbicide family (Davison and Smith 2007;Elseroad and Rudd 2011;Morris et al 2009). Efficacy of imazapic applications in Montana has been inconsistent (Mangold et al 2013), which encouraged us to investigate imazapic activity in Montana's semiarid climate. Imazapic is typically applied pre-or postemergent in the fall to control fall-emerging downy brome seedlings.…”

Imazapic Effects on Competition Dynamics Between Native Perennial Grasses and Downy Brome (Bromus tectorum)

“…Thus, if seeding natives in the fall, it may be beneficial to preemptively apply imazapic instead of reacting after downy brome seedling emergence. Mangold et al (2013) found that post-emergent applications provided more consistent short-term downy brome control, but their research did not evaluate impacts on newly-seeded desirable grass species. A South Dakota study showed success with low rates of imidazolinone herbicides (including 70 g ai ha 21 imazapic used in this study) applied pre-emergent to control weedy forbs and increase native grass seedling establishment (Bahm and Barnes 2011).…”