Herbicides The Benefits of Using Pre-Emergent Herbicides To Rehabilitate Cheatgrass-Infested Rangelands One of the greatest environmental challenges of the 21st century is cheatgrass invasion on western rangelands, resulting in the recurrence of catastrophic wildfires. With each wildfire season, more and more critical habitats are being converted from productive landscapes to cheatgrass dominance. In 2017, Nevada had over 600 individual wildfires, burning a total of 1.2 million acres. In an effort to minimize the negative effects of wildfires, the USDA-Agricultural Research Service-Great Basin Rangelands Research Unit has been conducting research on the use of pre-emergent herbicides to control cheatgrass and associated fine fuels. In our efforts, we use integrated rehabilitation practices rather than attempting to restore landscapes back to a pre-determined and often unobtainable reference state. We practice “rehabilitation” rather than “restoration” because “restoration is the intentional alteration of a site to establish a defined indigenous, historic ecosystem” which implies an ecosystem with no introduced species. Rehabilitation recognizes that an environment free of cheatgrass (and numerous other introduced species) is not realistic. Rehabilitation is a multi-step approach to “repair damaged ecosystem functions”. In 1999, a wildfire consumed more than 400,000 acres near Pumpernickel Valley, just north of Battle Mountain, Nevada. After the burn, a restoration team of numerous scientists and graduate students, funded by the Initiative for Future Agriculture and Food Systems (IFAFS), set up numerous small test plots (10’ x 10’ to 20’ 30’) in a portion of the burned area at the base of Rooster’s Comb along Izzenhood Ranch Road. The test plots included various weed control practices including herbicides, nitrogen immobilization practices and seeding mixtures. The IFAFS project’s mission over the 3-year study (2003-2006) was to conduct a series of experiments to determine the best methods to control cheatgrass and restore ecosystem function. The Izzenhood research site, however, was unsuccessful and by 2014 the site was still dominated by cheatgrass (Photograph 1). Photograph 1. IFAFS Izzenhood exclosure prior to the application of the pre-emergent herbicide, Landmark XP, and seeding treatments by the USDA-ARS-Great Basin Rangelands Research Unit.
By: Tye A. Morgan, Dan N. Harmon, Robert R. Blank & Charlie D. Clements USDA-Agricultural Research Service Great Basin Rangelands Research Unit 920 Valley Road, Reno, NV 89512 tye.morgan@ars.usda.gov We strongly suggest to apply the herbicide in early fall (September) prior to any fall cheatgrass emergence, fallow the treated area for one-year, and seed the following fall (Figure 1). This ensures that during the herbicide activity time, emergence of new cheatgrass (and other weedy species) will occur, but seedlings will not survive. When applied correctly (too high of rates or when perennials are green such as spring-time), any existing perennial grasses will survive this treatment. Figure 1. Time line of proper pre-emergent herbicide application and seeding dates for successful rehabilitation of cheatgrass dominated rangelands.
We then planted three types of seed mixes: A) Introduced; ‘Hycrest’ crested wheatgrass and Siberian wheatgrass @ 4 lbs/acre each, ‘Immigrant’ and ‘Snowstorm’ forage kochia @ 1 lb/acre each, B) Native; ‘Anatone’ bluebunch wheatgrass @ 6 lbs/acre, Sherman big bluegrass and Sandberg’s bluegrass @ 2 lbs/acre each, Wyoming big sagebrush and the native forb Bee plant @ 1 lb/acre each, and C) Combination of Native/Introduced; ‘Anatone’ bluebunch @ 4 lbs/acre, ‘Hycrest’ and Siberian wheatgrasses @ 2 lbs/acre each, Sandberg’s bluegrass, Wyoming big sagebrush, Bee plant @ 1 lb/acre each and ‘Immigrant’ and ‘Snowstorm’ forage kochia @ 0.5 lb/acre each. We recorded seeded species emergence, mortality, and establishment into the second-year as well as cheatgrass densities. HERBICIDE RESULTS
Landmark XP was extremely effective with over 98% cheatgrass control (Photograph 2). Pre-emergent herbicides can cost $5-$40/acre for the chemical and another $15-$65/ acre to apply. During the fallow year, with no cheatgrass present, resources such as soil nitrogen and moisture can accumulate without plant uptake (Figure 2 and 3), therefore increasing available resources for seeded species the following year. Photograph 2. Landmark XP applied to cheatgrass (and other weedy species) exceeds 98% control.
In 2015, the Great Basin Rangeland Research Unit started a new project in the IFAFS exclosure with the fall application of a pre-emergent herbicide, Landmark XP to control cheatgrass emergence and improve the opportunity for establishment of perennial grasses. The goal was to apply a pre-emergent herbicide, monitor soil nitrogen and moisture effects throughout the rehabilitation process, as well as record perennial grass emergence and establishment. We chose to use the pre-emergent soil active herbicide, Landmark XP (50% sulfometuron methyl + 25% chlorsulfuron + 25% inert material) @ 1.75 oz/acre rate, with a 1-year activity period. 14 JULY / AUGUST 2018
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