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Project description

Intensive grazing practices and revegetation for controlling medusahead in California grasslands. (02XN023)
Program Exotic Pests and Diseases Research Program
E.A. Laca, Agronomy and Range Science, UC Davis
M.R. George, Agronomy and Range Science, UC Davis
Host/habitat Rangeland; Grassland
Pest Medusahead Taeniatherum caput-medusae
Discipline Weed Science
Natural Systems
Start year (duration)  2002 (Three Years)
Objectives Determine the effect of intensive grazing during mid-spring, late-spring, mid and late-spring, and late-summer on medusahead populations.

Evaluate the effect of intensive grazing strategies on grasslands reseeded with a mix of native and introduced perennial and annual forage species.

Determine the population dynamics of dominant rangeland species after two years of intensive grazing and at least one year, and potentially two years, of reseeding.

Measure forage production and quality under all the proposed management practices.

We are proposing an experiment to evaluate use of intensive grazing practices and revegetation with perennial grasses to control medusahead, a noxious weed infesting over one million acres of California annual rangelands. In many rangelands, medusahead is the dominant species causing a reduction in rangeland productivity, species richness, plant diversity, and wildlife habitat. Currently, the only methods for controlling medusahead include burning and non-selective herbicides. Intensive grazing has been observed to reduce medusahead populations in Northern California rangelands, however, intensive grazing strategies have not been directly researched for controlling medusahead. The results from this and current research projects will determine the effectiveness of integrated strategies in improving productivity in rangelands infested with medusahead.
Final report "Precision" grazing was a powerful tool to control medusahead. This type of grazing requires application of high animal densities for short periods at a precise time to maximize the grazing pressure on medusahead and avoid detrimental impacts on other desirable species. Grazing in late spring or mid and late spring reduced medusahead cover by more than 80%. No other combination of dates was effective. It is essential to graze medusahead after the elongation of internodes and before the spikes or flower heads are fully exposed. Earlier grazing affected desirable species and allowed medusahead plants to grow back and form new seed heads. Later grazing allowed seeds to mature and replenish the seed bank. Usually, the period when medusahead has to be grazed is in late spring, ranging from late April to late May, depending on weather patterns. Reseeding with desirable species failed completely, most likely because of the timing of rainfall and drought periods during the season of establishment. Although seeded species did not become established, botanical composition of plots responded positively to effective grazing.

Objective 1: All grazing treatments were applied in 2004, and some have been applied again this season. Percent cover for each plant species was estimated for each plot on August 26, 2003 and March 5, 2004, before the grazing treatment was applied. Medusahead cover was estimated at the peak of the medusahead growth. Grazing during April and May, carefully scheduled on the basis of plant phenology, was very efficient reducing medusahead. The key was to graze when most other grasses had completed their cycle, but just before medusahead seed had matured. Grazing too early, as represented by the March grazing, is not very effective, probably because other grasses receive most of the grazing pressure, and medusahead has enough time to recover and complete its growth cycle with little negative impacts.

Objective 2: In fall 2004, immediately prior to the fall grazing treatment, one half of the plots were seeded with the following mix at 25 lbs/acre: 18% Berber orchardgrass (Dactylis glomerata), 19% purple needlegrass (Nassella pulchra), 20% blue wildrye (Elymus glaucus), 20% California brome (Bromus carinatus), and 20% perlagrass (Phalaris aquatica). Establishment of perennial grasses appears to be poor in most plots.

Objective 3: Botanical composition of plots was determined in August 26, 2003, March 5, 2004, April 20, 2004, June 14, 2004, and twice during spring 2005.

Objective 4: Forage in each plot was measured before and after the grazing treatment according to the original procedures. A database with all herbage mass measurements is almost completed. The use of a pressure plate and double sampling proved very efficient as a nondestructive technique that allowed work in relatively small plots. Measurements allowed detailed estimation of the rate of removal of forage per unit stocking pressure. This information can be used to gauge the number of animals necessary to achieve the desired level of control.

A fire destroyed the plots established during the first year of this project. The fire was an accidental result of a controlled burn conducted nearby by CDF. We submitted a claim for the estimated losses and it appears that we will receive funds to offset most of the loss. The net result of the fire is that we started the experiment again in a different area. As of today, we have conducted all baseline measurements of vegetation mass, botanical composition, and seed banks in the new site. Early grazing has already been applied in the new plots, and we are about to apply the late spring grazing treatment. Essentially we are at the same point we were last year in the original plots, and we are planning on completing the original plan, depending on the funds we receive form the insurance claim.

To date the project is proceeding according to the original schedule of activities. During this first year we have completed the initial vegetation surveys consisting of percent cover, forage production, and collection of samples for forage quality. Soil core samples were also collected to determine the initial seed bank composition. The first grazing treatment was applied during March 8 - 14 by rotating small groups of five to ten adult female sheep through the specified plots. Each plot that received the grazing treatment was grazed to the point at which approximately 1200 pounds per acre of dry forage was remaining. The duration of grazing varied from one to two days per plot. Sheep appeared to exhibit non-preferential grazing behavior by uniformly impacting the mosaic of grass and forbs present in each plot.

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