Effects of Imazapic on Target and Nontarget Vegetation During Revegetation

Authors: Sheley, Roger; CARPINELLI, MIKE - NRCS-ALBUQUERQUE NM; REEVER-MORGHAN, KIMBERLY - EUGENE OR; Vasquez, Edward

Submitted to: Extension Reports
Publication Type: Experiment Station
Publication Acceptance Date: 5/1/2008
Publication Date: 6/1/2008
Citation: Sheley, R.L., Carpinelli, M., Reever-Morghan, K., Vasquez, E.A. 2008. Effects of Imazapic on Target and Nontarget Vegetation During Revegetation . Extension Reports. Range Field Day 2008 Progress Report. Oregon State University Agricultural Experiment Station, Special Report 1085. Burns, OR. pp. 43-47.

Interpretive Summary: Medusahead is an introduced, winter-annual grass covering millions of acres of western rangelands. It forms large monocultures and has a dense thatch cover that resists the establishment of desirable vegetation. Prescribed fire can remove medusahead litter and improve plant establishment. Medusahead control is fundamental to establishing desirable vegetation that will, in turn, resist future invasion. Imazapic is an effective herbicide for control of medusahead, but more information is needed on its effects on desirable vegetation. Therefore, existing medusahead infestations were burned at two different sites in June 2003 to test how Imazapic application rate and timing affected medusahead, desirable seeded plant species, and other nontarget vegetation on burned and unburned rangeland in southeastern Oregon. Following the burn, imazapic was applied at seven increasingly concentrated rates between July and October of 2003 in a randomized strip-plot design field experiment. In November 2003, seven different desirable plant species were drill-seeded separately across the imazapic areas. Data on cover and density of medusahead and seeded plant species were collected in 2004 and 2005. Cover data of nontarget vegetation were collected in the summer of 2005. Medusahead cover was the highest in control plots that did not receive imazapic and lowest in plots that received the highest herbicide rates. Seeded plant species established in the study plots, but their response to herbicide rate showed few consistent patterns. For example, some of the seeded plant species showed little response to herbicide, whereas others appeared to establish best at different herbicides rates, depending on site and whether the plots were burned or unburned. Site and burn treatment also affected how imazapic rate or application month influenced cover of perennial or annual grasses or forbs.

Technical Abstract: Medusahead is an introduced, winter-annual grass covering millions of acres of western rangelands. It forms large monocultures and has a dense thatch cover that resists the establishment of desirable vegetation. Prescribed fire can remove medusahead litter and improve plant establishment. Medusahead control is fundamental to establishing desirable vegetation that will, in turn, resist future invasion. Imazapic is an effective herbicide for control of medusahead, but more information is needed on its effects on desirable vegetation. Therefore, existing medusahead infestations were burned at two different sites in June 2003 to test how Imazapic application rate and timing affected medusahead, desirable seeded plant species, and other nontarget vegetation on burned and unburned rangeland in southeastern Oregon. Following the burn, imazapic was applied at seven increasingly concentrated rates between July and October of 2003 in a randomized strip-plot design field experiment. In November 2003, seven different desirable plant species were drill-seeded separately across the imazapic areas. Data on cover and density of medusahead and seeded plant species were collected in 2004 and 2005. Cover data of nontarget vegetation were collected in the summer of 2005. Medusahead cover was the highest in control plots that did not receive imazapic and lowest in plots that received the highest herbicide rates. Seeded plant species established in the study plots, but their response to herbicide rate showed few consistent patterns. For example, some of the seeded plant species showed little response to herbicide, whereas others appeared to establish best at different herbicides rates, depending on site and whether the plots were burned or unburned. Site and burn treatment also affected how imazapic rate or application month influenced cover of perennial or annual grasses or forbs.