Grazing Strategies to Control Medusahead in California

Final Report for SW06-038

Project Type: Research and Education
Funds awarded in 2006: $138,539.00
Projected End Date: 12/31/2010
Region: Western
State: California
Principal Investigator:
Expand All

Project Information


We studied precision grazing to control medusahead. High-density, short-duration grazing when medusahead is at the internode elongation and boot stages dramatically reduces medusahead infestation. In order to achieve satisfactory control, grazing must apply a stocking rate greater than 1 AUM/ac within the two-three weeks when medusahead is susceptible to defoliation. Susceptible phenological stages are between elongation of internodes and milk stake and are predictable, but vary over regions. Barbed goatgrass, another noxious invasive grass, also has late phenology like medusahead, and it is susceptible to defoliation, but it is more resistant than medusahead. Models to forecast readiness for grazing control were not better than predictions based on historic information for each site, although there is some indication that further research can accomplish more accurate forecasting of phenological stages. Based on recommendations from stakeholders, we also tested mowing and non-selective herbicides as additional control tools that can be used with a precision approach. Mowing had dramatic control effect when timed correctly, but it is limited to areas without rocks and that are relatively level. Low-moisture supplement placed in medusahead patches increased grazing intensity and resulted in a reduction of medusahed infestation, but the effects were localized. Detailed study of phenology revealed a bimodal phenology, which could limit control by precise grazing, mowing or herbicide application. Results and approaches were disseminated in several regional and national meetings, and by direct communication with producers. Overall, results underscored the potential for precise timing of management options, but also identified areas that require more detailed investigation such as phenology and chemical interference by medusahed.

Project participants

This project was very successful because the work of many collaborators and ranchers. In addition to the gracious and inquisitive ranchers who kindly allowed us to work in their land and who shared their knowledge and time with the group, we had several participants who were part of the core group. These people and their institutions at the time of the project are listed here. They are coauthors of this work and deserve recognition.

Mel George, Extension Specialist, Plant Sciences MS 1, One Shields Ave., University of California, Davis, CA 95616, 530-752-1720, [email protected]

Joseph DiTomaso, Extension Specialist, Plant Sciences MS 1, One Shields Ave., University of California, Davis, CA 95616, 530-754-8715, [email protected]

Morgan P. Doran, Livestock & Natural Resources Advisor, University of California Cooperative Extension, 501 Texas Street, Fairfield, CA 94533, 707-435-2459 [email protected]

John Harper, UCCE Livestock and Natural Resources Advisor, Mendocino and Lake Counties, 890 N. Bush Street, Ukiah, CA 95482-3734, 707-463-4495, [email protected].

Stephanie Larson, Livestock & Natural Resources Advisor, Sonoma County, University of California Cooperative Extension, 133 Aviation Boulevard, Suite 109, Santa Rosa, CA 95403, 707-565-2621, [email protected].

Sheila Barry, Natural Resources Advisor, UCCE Santa Clara County, 1553 Berger Drive, San Jose, CA 951112, 408-282-3106, [email protected].

Bill Frost, UC-ANR Natural Resources and Animal Agriculture Program Leader, Director, UCCE El Dorado County, 311 Fair Lane, ?Placerville, CA 95667, 530-621-5502, [email protected].

Josh Davy, Program Representative, ?UC Cooperative Extension, ?Tehama, Colusa, and Glenn Counties, ?1754 Walnut St., ?Red Bluff, CA 96080, 530-527-3101 ext. 5, [email protected].

Theresa Becchetti, Livestock and Natural Resource Advisor, University of California Cooperative Extension, Stanislaus and San Joaquin Counties, 3800 Cornucopia Way, Suite A, Modesto, CA 95358, 209-525-6800, [email protected].

Royce Larsen, Area Watershed / Natural Resource Advisor, University of California Cooperative Extension, 350 N. Main Street, Suite B, Templeton, CA 93465. 805-434-4106 Direct line, 805-781-5940 Front Desk San Luis Obispo Office, 805-434-4881 Fax, 805-781-4316 Fax San Luis Obispo Office, [email protected].

Vance Russell, Program Manager, Audubon California, 5265 Putah Creek Road, Winters, CA 95694, 530-795-2921, [email protected].

Larry C. Forero, Livestock and Natural Resource Farm Advisor, UCCE, Shasta and Trinity counties. 1851 Hartnell Avenue, Redding, CA 96002-2217, [email protected].

Roger Ingram, Acting County Director and Livestock/Natural Resources Advisor, Placer-Nevada Counties, University of California Cooperative Extension, 11477 E Ave., Auburn, CA 95602, Phone: (530) 889-7385, Fax: (530) 889-7397, Email: [email protected].

Project Objectives:

Objective 1. Design a simple and cost-effective “precision” grazing method to control medusahead (Mh) and incorporate it into the grazing systems of California annual rangelands.

Objective 2. Study the effects of spatial distribution of attractants such as supplement on spatial distribution of grazing pressure and use new knowledge to implement supplementation methods to reduce Mh infestations.

Objective 3. Develop and implement a site-specific and simple system to identify and forecast the period of Mh’s greatest susceptibility to mowing and grazing and establish a warning system for ranchers to accurately time grazing.

Objective 4. Disseminate, demonstrate and document results in extension fact sheets, field visits and newsletters by Farm Advisors.


Medusahead (Taeniatherum caput-medusae L. Nevski), an invasive grass from Eurasia, has invaded one million acres of California annual grasslands, oak woodlands, chaparral and Great Basin grass and shrublands. Once Mh invades, it becomes a detriment to the whole ecosystem, reducing biodiversity, commercial and wildlife grazing value and recreation value of rangelands. Reduction of medusahead will result in greater biodiversity, lower risk and intensity of fires and greater grazing capacity.

Medusahead (Mh) often accumulates a dense thatch layer that appears to promote its own dominance by inhibiting other plant species (Bastow et al., 2008; Coleman and Levine, 2007; Kyser et al., 2007; Monaco et al., 2005; Young, 1992). Thatch accumulation from Mh and other invasive species may have important effects on seed germination and seed or seedling survival through alteration of light level and quality (Coleman and Levine, 2007; Jensen and Gutekunst, 2003), disruption of soil-seed contact (Bosy and Reader, 1995; Rotundo and Aguiar, 2005) or allelopathy (Olson and Wallander, 2002). Medusahead seeds and seedlings possess morphological features and physiological characteristics that may increase their ability to germinate and survive in dense thatch (Northam et al., 1996; Young et al., 1968) DiTomaso, personal communication).

Ranchers spent roughly $5 billion for invasive weed control in 1998 (Pimentel, 2005). In California grasslands, Mh is unpalatable to herbivores and slow to decompose (Miller et al., 1999). Control methods for Mh used in the past have been costly and ineffective. Fire has been used, but California’s air quality restrictions make it difficult to obtain burn permits, and risk of property loss is high due to the interspersion of development with rangelands. Traditional chemical treatment has reduced efficacy because there are no selective herbicides. Rangeland managers need to know when optimal control can be achieved through grazing or mowing. Use of non-selective herbicides can also be considered under the same general scheme as grazing and mowing, whereby the emphasis is on precise timing of applications.

Although this work focuses on medusahead, we found barbed goatgrass (Gg, Aegilops triuncialis L.) in most experimental sites and recorded some effects on this noxious grass. Both Mh and Gg are characterized by late phenology and very low palatability, posing similar management challenges. Thus, we report some results for Gg along with those for Mh.

Barbed goatgrass was probably first introduced to California around 1915 (DiTomaso et al. 2001) from Mediterranean Europe and western Asia (CDFA 2005). Like medusahead, it can crowd out other valuable range species, reducing forage quality and quantity and causing injury to livestock when its barbed awns became lodged in their noses, mouths or eyes (Bovey et al. 1960; Harris and Goebel 1976; Kennedy 1928). It is estimated that the livestock capacity of a grassland infested with barbed goatgrass is reduced by 50% to 75% (Jacobsen 1929). Since its introduction, barbed goatgrass has spread rapidly. The barbed awns of this species facilitate long distance dispersal by attaching to clothes or animal fur (DiTomaso et al. 2001; DiTomaso and Healy 2007). By the late 1920s it had spread to thousands of acres, but the infestations were local and restricted to two counties, Calaveras and El Dorado (Talbot and Smith 1930). Nevertheless, barbed goatgrass expanded its range in the Central Valley and coastal foothills and was reported to occur in about 13 counties by 1973 and 21 California counties by 1995 (Peters et al. 1996). Today, barbed goatgrass is a state-listed noxious weed in California (CDFA 2005; DiTomaso et al. 2001) and Oregon (ODA 2007).

We conducted several studies to develop novel methods to control medusahead that are cost-effective and simple. We studied precision grazing with sheep and cattle, mowing, application of glyphosate and concentration of grazing with attractive livestock supplement. All methods are based on a detailed knowledge of the phenology of medusahead and require careful monitoring of the stages of noxious invasive species and more desirable exotic species.


Click linked name(s) to expand/collapse or show everyone's info
  • Jim Yeager


Materials and methods:

We conducted six series of activities at private ranches:

1. Determination of stocking density and duration to control medusahead by precision grazing in two ranches.

2. Use of low moisture blocks as attractants for cattle in five ranches.

3. Models to predict time of medusahead susceptibility to grazing in eleven counties of California.

4. Evaluation of precision application of herbicide and mowing to reduce medusahead.

5. Assessment of nutritional quality of medusahead and goatgrass at various phenological stages.

6. Evaluation of the economical impacts of management options for medusahead control.

In addition to these activities at ranches, we conducted additional experiments and measurements in the laboratory to determine basic characteristics of medusahead biology such as germination, grain development and viability, and competition with annual ryegrass. The methods used for each experiment are briefly described in the subsections that follow.



Phenology samples were collected in 16 sites over 11 counties in California (Figure 1 and Table 1). Sites were selected by Farm Advisors from the respective counties based on their knowledge of Mh distribution and accessibility of sites. The sites spanned a large latitudinal range and ranged from the Coastal Range to the east side of the Central Valley.


Phenological stages of medusahead were defined at the tiller level based on preliminary observations. Stages were selected such that they are relevant to management decisions such as grazing and mowing. Sampling was stratified in each site according to landscape position and aspect. At each strata, observers collected several grab samples of vegetation within a couple of feet. Grab samples were placed into one bag and labeled with all relevant information including geographical coordinates, date and site name. Sample bags were immediately delivered to the lab or refrigerated until shipped. Once in the laboratory, samples were recorded into a database and scored for proportion of tillers of Mh in each phenological stage. The database was complemented with data on soil series and daily weather from the nearest station (Table 1).

Additional samples were taken to perform detailed comparison of phenological stages across species at a subset of dates and locations. Large grab samples were collected in transects spanning hundreds of meters. Each tiller or branch was identified to species and scored for phenological stage at the lab.


First, we calculated a weighted average phenological score (“pheno score”) for each site and date observed using the proportion of tillers in each stage as weights. Total proportion of tillers in stages susceptible to control (“proportion susceptible”) was also calculated as a response variable. Pheno score was analyzed with mixed nonlinear models including degree-days (cumulative days with temperatures above 5 C), day of the year, days since start of season, precipitation, number of long days (days longer than 13 h) and number of cold days (days with min. temperature below 0 C).

Second, we calculated the proportion of Mh tillers in susceptible stages (R4-R8 as defined below). These stages were considered susceptible to control because plants cannot recover from defoliation after R4 and viable seed is not produced before stage R8. The proportion susceptible was modeled as a function of day of the year for each site.

Third, we calculated the proportion of tillers in each phenological stage for the main rangeland species and made histograms for different dates to have quantitative description of the differences.

Precision grazing to control medusahead.

Treatments to control Mh and Gg are based on a conceptual model of phenology and impact of grazing at different times with various animal densities (Figure 2). Species are grouped into early and late based on the date when most of the reproductive stage R4 starts. Medusahead and goatgrass are represented by the late peak of flowering (dashed line) in the middle panel of Figure 2, whereas more desirable species are depicted as flowering earlier (continuous line). The top and bottom graphs represent the results of grazing with the same stocking rate applied in a long grazing period with low stocking density or in a short period with a high stocking density. The vertical width of the white area at any given date represents the expected proportion of medusahead resulting from starting the grazing period on that date. The blocks labeled “Long grazing” and “Short grazing” represent the theoretical optimal grazing periods to reduce the proportion of weed. A long grazing period is hypothesized to be less effective in controlling a weed with late phenology, such as Mh and Gg, because many plants have a chance to produce seed before they are grazed. In theory, the best grazing scheme would be to graze all plants after most desirable species produced seed, but before weedy grasses had time to become excessively unpalatable or set seed.

Precision grazing with sheep: Antibodies site


The study area consisted of a 25-ha pasture in a ranch in Yolo County, CA. Regional climate is Mediterranean with a 30-year mean annual precipitation of 46 cm with 88% occurring from October through March. Mean annual temperature is 16 C. The soils at the study area were a Myers heavy clay and Hillgate loam complex with slopes of no more than five percent. The site was grazed by roughly 100 Dorset and Suffolk ewes from November through May, supplemented with alfalfa hay. The ewes most heavily grazed areas dominated by annual ryegrass (Lolium multiflorum Lam.), soft chess (Bromus hordeaceus L.), filaree (Erodium spp.) and rose clover (Trifolium hirtum All.) near the supplementation site, as well as a frequently flooded riparian area dominated by ryegrass and Bermuda grass (Cynodon dactylon L. Pers.) and bur clover (Medicago polymorpha L.). These areas made up roughly 35% of the pasture and contained little or no Mh. The remaining pasture was dominated primarily by Mh and mixtures of Mh, ryegrass, soft chess, rose clover and barbed goatgrass (Aegilops triunculatis L.).


We designed treatments and measurements to answer the following questions:

1. Within treated plots, did variation in treatment factors (utilization and duration from precision grazing as well as reseeding) affect response variables?

2. On average, did precision grazing and/or reseeding affect response variables when compared to non-grazed exclosures or continuously grazed control areas?

3. What was the potential for Mh escape from precision grazing treatments due to grazing heterogeneity or variability in the phenological development of Mh within plots?

In late February 2007, 12 main plots were selected in Mh-infested areas in the site. Main plots were 0.2 ha and divided into two sub-plots of 0.1 ha. Nominal treatments consisted of a three-way factorial:

1. Four targeted green forage utilization levels (50, 60, 70 and 80% of green forage).

2. Two intended durations of grazing (7 and 14 days) by 100-kg ewes.

3. Two reseeding levels (yes or no).

The number of ewes stocked in each pasture was set to achieve the targeted utilization rate over the targeted duration (Table 2). Because a regression-based set of analyses were planned, not all nominal utilization x duration combinations were replicated. Treatments were assigned randomly to main plots. Reseeding levels were randomly assigned to each of the sub-plots. A botanical composition survey was conducted in all 12 main plots in March 2007 before fence completion or initiation of grazing treatments.
Plots were fenced during the late March 2007. In each plot, we created two grazing exclosures one meter in diameter in areas that were infested with Mh. Based on a visual estimate of forage mass and assuming an intake rate of 3% body weight per day, sheep stocking rate was set to achieve the nominal utilization and grazing duration. In each plot, grazing was initiated when at least 50% of the Mh appeared to be beyond the late elongation stage and terminated when the target utilization appeared to be achieved according to visual assessment of the whole plot.

On December 12 2007, at the onset of winter precipitation, sub-plots assigned to reseeding were lightly disked and broadcast seeded with a mixture of annual and perennial grasses and annual legumes. The species were chosen to represent desirable forage species already thriving at the site (ryegrass, soft chess and rose clover), as well as other forage legumes and native grasses which are hypothesized to be competitive with Mh [T. subterraneum L. (subterranean clover), Elymus elymoides (Raf.) Swezey (squirreltail, a perennial species native to California), and B. carinatus (California brome, a short-lived perennial native to California)]. Later lab tests showed that the California brome seed had a germination rate of only 15%, much lower than that indicated on the commercial label. The seeding had no appreciable effects, except for the establishment of subclover in the area. None of the perennial grasses established to a detectable level. Seeding effects are thus not considered any further in this report.

In addition to the exclosures, we used the pasture immediately adjacent to the treated plots as a control reference. These areas were continuously available to ewes not in the fenced plots and were similarly infested with Mh as the treated plots. Ewes were fed 0.06 kg of soybean meal per day of grazing.


Surveys were conducted at selected times before or after grazing or reseeding. These surveys were designed to provide data about:

1. The year-to-year change in botanical composition (coverage of Mh, Mh thatch, non-Mh species and bare ground) at time of “peak green mass” (early-middle March 2007 and 2008) caused by variation in the precision grazing factors.

2. The apparent forage utilization achieved in each precision grazed plot, the change in Mh coverage due to grazing and the phenological state of Mh before and after grazing (April 2007).

3. The impact of the precision grazing treatments on the end-of-season Mh coverage and seed production of Mh and non-Mh species in the same year as grazing (June 2007) and the following year (June 2008).

After Mh seed maturation but prior to Mh seed shatter, a survey and sampling campaign was conducted to assess Mh and non-Mh seed production, final Mh absolute coverage and final dry mass in treated plots, exclosures and in continuously grazed areas outside the treated plots. The survey was conducted from June 15-17, 2007. Twenty-five observations of Mh absolute coverage within 0.1 m2 quadrat were collected in each plot over a uniformly distributed grid. The center 10 x 15 cm of each plot was clipped and all vegetation as well as seeds on the soil surface were collected. These samples were intended to provide a mean estimate of seed productivity over each plot such that effects of plot-level treatments could be assessed.

Clipped vegetation and seeds were also collected from 0.1 m2 quadrats inside each exclosure (two per plot) and from a treated area within one to two m of each exclosure (two per plot) to facilitate comparison between precision grazing and non-grazed controls. As an additional control reference, quadrats were clipped from untreated areas within one to two m of treated plots that had an outside border with the continuously grazed pasture (two-four quadrats per plot with an outside border). Samples were dried and weighed as described above. Seeds of Mh and all non-Mh species were removed and counted from each sample. On June 15-16, 2008, the survey was modified such that three 0.1 m2 quadrats were randomly placed on the same grid within each sub-plot and clipped at 1 cm height to provide dry forage mass and seed counts. On June 7-14, coverage of Mh was observed in each treated plot on 70 0.1-m2 quadrats on a uniformly distributed grid within each plot.


First, we analyzed Mh cover and seed production in 2007 as a function of grazing duration, apparent utilization and their interaction. Stocking density (ewes per plot) was highly dependent on grazing duration and apparent utilization and, therefore, provided little independent explanatory power. Where appropriate, pre-treatment plot means of absolute Mh coverage or mean proportion of stems in the targeted phenological stages were included in the model as covariates. After reseeding (December 2007), response variables recorded subsequently were averaged at the sub-plot level and the model included reseeding (yes or no), all interactions of reseeding with the main plot factors and a (random) plot x grazing duration x apparent utilization interaction. The significance of model terms including reseeding were tested using the residual (experimental) variance estimate, and the significance of the main plot factors were tested using the variance estimate for the plot x grazing duration x apparent utilization interaction. Second, we compared seed production of Mh and other species in grazed vs. ungrazed areas. Ungrazed areas were exclosures inside the grazed plots and open areas outside the treated plots.

Precision grazing with cattle: OWNS site


We conducted a grazing experiment on a 33-acre pasture near Willows, CA where cattle were used during the period of peak medusahead susceptibility to grazing. Soils at this site are mostly Altamont soils, 15-30% slopes (AdD), with patches of Altamont-Nacimiento association, 3-15% slopes (AmC), Millsholm very rocky sandy loam, 30-65% slopes (MuE) and Zamora silty clay loam, 0-2% slopes (ZbA). Average rainfall and temperature are about 470 mm and 16 C. Treatments were combinations of high and low animal density with short- and long-grazing periods to obtain a series of levels of utilization.


The experiment consisted of a factorial of two pasture sized and two grazing durations to achieve a nominally constant stocking rate (Table 3). Each treatment was repeated in each of three blocks. Animals were crossbred yearling steers, each representing about 0.65 animal units (AU).


Herbage botanical composition and Mh/goatgrass/star thistle phenology and coverage surveys were completed before grazing in April 2008 and after animals were removed from each plot in May 2008. Botanical composition by species was assessed visually and scored as percentage of total cover in several dozen points per pasture. Locations of observation quadrats were recorded with a GPS with a precision of ~ 30 cm. Herbage growth and disappearance were assessed by establishing two areas where grazing was excluded in each plot, and by measuring herbage mass before and after grazing outside the exclosures and after grazing inside the exclosures. A seed collection survey was also completed in June 2008 to determine the impact of grazing on seed produced by the most common species in the grazing season. Botanical composition of grazed areas was measured again in June 2009 after a complete grazing season under the regular stocking after fences had been removed.


We built a GIS for the pasture and stratified observations by the type of soils as evident from the remote imagery available (Figure 3). Response variables were analyzed with mixed effects models, including fixed effects for stratum and the 2x2 factorial of pasture size and grazing duration and random effects for pasture. Stocking rate (AUM/ac) was included as a covariate to account for potential effects of deviations from the nominally constant stocking rate. Spatial correlation of residuals was tested and modeled with variograms using the nlme package (Pinheiro and Bates 2001) of the R system (R Development Core Team 2010). Transformation and variance functions were used when necessary to account for spatial correlations and heterogeneity of variance.

Effect of low-moisture supplement to promote grazing of medusahead.


We trained livestock to find and consume a highly palatable low-moisture supplement offered in plastic tubs marked with flags early in the spring at the CHCK, GNSL, BRDF, GLTN, SLT and DLCN ranches.


In each site we selected two areas where medusahead was abundant, separated by at least 200 m. One of the areas was selected to receive supplementation treatment and the other was used as control. Supplement was placed in a cross pattern in four points, each located 10 m from the center of an area with high medusahead density (Figure 4). A series of radial transects with grazing exclosures at 20, 40, 60 and 90 m from the center were permanently marked on the treated and control areas.


We measured botanical composition, degree of grazing and herbage height prior and after grazing in the springs of 2006, 2007 and 2008. Botanical composition and grazing was assessed every 5 m on the transects, inside and outside the exclosures. Several 0.9 m2 quadrats were clipped inside and outside exclosures to determine herbage mass.


Proportion of medusahead cover and proportion of area grazed and stubble height were analyzed with a mixed model, with random effect for ranch and fixed effects for a complete factorial of location (inside exclosure, outside exclosure and grazed transect), distance from supplement (0-35, 35-70, and 70-105 m) and period (year of application of supplement prior to grazing, end of first grazing season and end of second grazing season). Variables were transformed as necessary to achieve normality and homogeneity of variance.

Effect of timing and intensity of clipping on medusahead and goatgrass.


The study was conducted at the Antibodies Ranch in Yolo County, CA. The soil types in the ranch are Myers Clay (fine, smectic, thermic, Aridic Haploxerert) and Hillgate Loam (fine, smectic, thermic, Typic Palexeralf). The dominant species are medusahead, barbed goatgrass (Aegilops triuncialis), rose clover (Trifolium hirtum), bur clover (Medicago polymorpha), Soft brome (Bromus hordeaceus), filaree (Erodium brachycarpum), oats (Avena sp.) and annual ryegrass (Lolium multiflorum).


Two 6 m x 26 m areas were used in this study, one dominated by barbed goatgrass and the other dominated by medusahead. In each area we established 54 plots (50 cm x 50 cm) separated by 50 cm alleys. A factorial of nine defoliation dates and three defoliation heights were replicated twice in a completely randomized design. Defoliation intensities (heights) were three, six and nine cm from the ground. The nine defoliation dates were April 15, 19, 25, 28, and May 1, 4, 8, 12, 16, 2007. These dates were chosen to begin defoliation during the late vegetative stages (V3) and continue through completion of kernel elongation inside the florets (R7) or milk stage (R8).


Canopy height and botanical composition of the defoliated plots were surveyed before defoliation. Each plot was defoliated once and then left undisturbed until the end of the season. Immediately prior to defoliation, five plants of medusahead or barbed goatgrass from each plot were collected to determine their phenological stage. Clipped herbage from each plot was collected and dried to determine biomass and number of seedheads. A final survey of botanical composition, number of seedheads of medusahead and barbed goatgrass and canopy height of all defoliated plots was conducted on July 12, 2007.


Data were analyzed as a factorial of phenological stage and height of clipping in a completely randomized design. Medusahead and goatgrass were analyzed as separate experiments because they were in separate areas of the ranch.

Large-scale mowing of medusahead.


Medusahead has invaded a large proportion of the Dunnigan Hills region of Yolo County, CA. This region is characterized by gentle slopes and little presence of rocks. Most areas have a history of rain-fed barley production. Old fields have very high density of medusahead, which reduces the grazing value. This area is characterized by very heavy medusahead infestation. In some patches medusahead thatch has accumulated to the point that it smothers itself and promotes patches of secondary succession where thistle is abundant.


The ranch owner mowed several acres on May 2007, when most of the medusahead was at stages R4-R5. We selected additional areas and established five 100 m transects in heavily infested areas. Two 6 m wide and 25 m long swaths were mowed across each transect.


Botanical composition was estimated visually every 5 m in each transect immediately prior to mowing, at the end of the season and at the end of the following growing season. Number of seedheads per unit area was measured in several locations in the mowed and control areas.


Due to the observational nature of the trial, we simply estimated the means and variance of seed production in mowed and control areas and documented the effects of mowing with photographs.

Application of glyphosate.


This test was conducted at the CHCK ranch in San Joaquin County, CA. The site is grazed seasonally by yearlings and cow-calf pairs. An area with heavy infestation of medusaehad was identified and fenced early in the season to prevent grazing and trampling.


We tested the application of glyphosate at three phenological states of Mh. We hypothesized that applications that are too early will lead to excessive reduction in forage production, because glyphosate would kill all plants before forage accumulation. Applications that are too late may result in poor control because seeds that are close to viability may become viable before the herbicide kills the plant. Glyphosate was applied at 16 and 32 oz. per acre in a 1% water solution early- (March 5, 2008), mid- (March 19, 2008) and late- (May 2, 2008) season. Each combination of dose and date was applied to four plots. Each plot had a control band in the center where no herbicide was applied. The design was a factorial of dose and date of application in a completely randomized design.


Proportion of cover by medusahead was determined prior to treatment, at the end of the first growing season and at the end of the following growing season. Herbage was clipped to determine herbage mass per unit area.


Proportion of medusahead was analyzed as a factorial of herbicide dose, date of application and original level of infestation.

Comparative nutritional quality of medusahead and goatgrass.


Samples of annual ryegrass (Lolium multiflorum), medusahead and goatgrass were obtained at the Antibodies site (described above).


Grass samples were collected over the season at various phenological stages, ranging from V2 to R7. A good quality alfalfa hay was included in the sample to provide a basis for comparison. Thus, "treatments" were species and phenological stages.


Several 250 mg samples of medusaehad, barbed goatgrass, alfalfa and annual ryegrass ground to 1 mm were placed in syringes with rumen inoculum in a 39C bath to simulate the conditions in the cow's rumen. Gas production from the fermentation was recorded for seventy-two hours, with sample number, syringe number and volume of gas being recorded. The gas method was used to gather information on the rate of decomposition for samples of different phenological stages of the plants and can be used to estimate digestibility of samples. Medusahead and goatgrass samples were sent to the UC Davis NR Lab for determination of crude protein, acid detergent fiber (ADF) and silica content.


Gas production was modeled as an asymptotic nonlinear function of incubation time with different coefficients for each species and phenological stage. Silica, crude protein and ADF content were modeled with factorial effects of species, phenological stage and their interaction.

Medusahead germination and interference.

Seed germination and growth experiments were conducted using six species, hereafter referred to as “target” species that are common to the annual grasslands of California, and often found growing next to Mh. Seeds from all species, except purple needlegrass, were collected from BBCT ranch in May and June of 2003. Purple needlegrass seeds were collected from potted plants grown in May of 2000 and 2001. Plants were grown from seeds collected in May 1997 from the Sierra Foothill Research & Extension Center, Yuba Co. Seeds were stored until used in the experiment in either plastic or paper bags/envelopes in a dark cupboard at room temperature.

Experiment 1. The first trial examined whether seed germination and growth of target species are inhibited in the presence of Mh seeds, awns and litter. Seeds were germinated in 10-cm diameter plastic Petri dishes lined with four layers of paper towel (Kimberly-Clark Corporation, USA), moistened twice daily. Twenty seeds of each target species were sown under each of the following treatments:

1) No Mh seeds, awns, inflorescences or straw (Control),

2) 10, 20 or 40 Mh seeds,

3) 20 Mh awns cut into small pieces (ca. 0.0067 g),

4) 10 Mh inflorescences (ca. 0.119 g),

5) 10 Mh straws (ca. 0.112 g),

6) 10 inflorescences and 10 straws (ca. 0.445 g).

“Inflorescences” consisted of the remains of the spikes without the culm after seeds disarticulated. “Straws” were the culms that supported the spikes. Each treatment was replicated four times (four Petri dishes), which yielded a total of 32 dishes for each of the six species tested. Figure 1a illustrates the experimental set-up where each Petri dish was divided in four equal sectors. Each sector received either Mh or one of the target species in an alternating fashion. Except for the controls, each dish had Mh and a single target species. Germination was monitored from December 25, 2006 - January 10, 2007, starting four days after seeds were placed in the dishes. The experiment terminated when the number of germinating seeds had reached an asymptote. Shoot dry mass of 10 randomly selected seedlings in each Petri dish were measured at the end of the germination trial.

Experiment 2. A second trial was conducted to determine if Mh’s effect on competitors is mediated by released chemical substances. The general set-up and protocol used was the same as described in Trail 1. Trial 2 consisted of the following treatments:

1) No Mh seeds or awns (Control),

2) 10, 20 or 40 Mh seeds, and 3) 20 Mh awns (ca. 0.0067 g).

Each treatment included four replicates requiring a total of 20 Petri dishes for each of the six species tested. In Trial 2, Mh seeds or awns were placed in the dishes and watered first and then removed four days later, after seeds had germinated. After removal of all Mh tissues, 20 seeds of a target species were sown in the same Petri dish on the areas where Mh had been placed. The trial began on February 24, 2007 and ended on March 14, 2007, when the number of germinating seeds reached an asymptote.


Germination was analyzed as a survival or time to “failure” process using an interval-censored approach, where the response variable was the time to germination (“failure”) and the frequency was the number of seeds germinated during the 24 hours between observations. All seeds that did not germinate by the end of the experiment were right-censored. We tested the Weibull, exponential and lognormal distributions. Residuals were tested with quantile plots. The best fit and distribution of residuals were achieved with the lognormal distribution, so we chose it for the final analyses. Treatment effects were tested by likelihood ratios at the 1% level. Estimated parameters of significant effects were used to generate predicted curves for cumulative germination and 95% simultaneous confidence bands as a function of time. This constitutes a conservative approach to comparing germination curves across treatments. Comparisons among species are of exploratory nature, since no a priori hypotheses were posed in this regard. In order to test for dose responses to the number of Mh seeds, we re-analyzed the subsets of data corresponding to treatments with 0 to 40 Mh seeds in both trials. Number of Mh seeds was specified in the model as a continuous variable and we tested for linear and quadratic effects, as well as for interactions between species and number of seeds. Shoot masses were averaged for each Petri dish, and the averages were analyzed with a simple linear model with effects for species, medusahead treatment and their interaction. The model implies a completely randomized design where each treatment had four replications. Box-Cox transformations were used as necessary to achieve homogeneity of variance in the residuals. We separated means using Tukey’s HSD.

Research results and discussion:

Phenological information about Mh and associated species was collected in twelve sites in eleven counties of California during the growing seasons in 2006, 2007 and 2008. Medusahead is characterized by a late development relative to other species, which gives us a window to apply control methods that are not selective. By the time Mh produces inflorescences, most of the more desirable associated species have already produced enough seed to have a good stand in the next season.

After it produces an inflorescence, Mh is very unpalatable and strongly avoided by livestock. Thus, control methods must be applied late enough to allow for desirable species to reseed themselves, and early enough to prevent Mh from flowering and setting seed. These conditions restrict the time window to about two-three weeks in late spring. Given the short time window, land managers must forecast the time of control to get all resources ready for treatment. We classified Mh phenological stages and developed models to predict phenology based on location and climate factors. The best timing for control can vary widely in the different counties in California.

Statistical models, including all variables, were tested and reduced by removing non-significant terms. A set of models was developed, but the data did not reveal any strong predictors of phenology beyond date and associated measures. The variation among sites was not explained by any of the predictors tested. Phenological stage was given a numerical value according to, and modeled as, a sigmoid function (logistic) of days since the beginning of the season. A different set of parameters was obtained for each location, and then parameters were studied as a function of latitude. The parameter that reflects the timing of reproductive stages was significantly related to longitude, latitude, degree-days and their interactions (Table 4); however, unexplained variation was large and not conducive to make predictions more useful than setting dates for each site based on information from past years.

Analyses indicate that there are significant regional differences in the phenology of medusahead (Figure 6). Whereas in Glenn and Stanislaus Counties medusahead reached late vegetative state April 20, 2006, that phenological stage was not reached until May 8 in Alameda and May 4 in Mendocino. These last two counties are characterized by having greater rainfall and lower temperatures than the rest in the spring. Further modeling is necessary to fully explore the potential causes of differences in phenology. Regardless of the cause of differences, the phenology curves for a site did not differ over years. Thus, site-specific models or historic dates should be used, keeping in mind that there may be a difference of more than 45 days between sites in the date of peak susceptibility of medusahead.

Both the phenology of weeds and desirable species are important for the purpose of grassland management. Thus, we sampled and analyzed detailed phenological information for multiple species. Two questions were addressed: Does medusahead really flower much later than the most important desirable grasses? Is medusahead phenology compact in time or does it have a wide range of variability? The answer to the first question is crucial for the reproduction and survival of desirable species in areas treated to control medusahead. The answer to the second question determines to efficacy of precisely timed treatments. A wide variation in medusahead phenology within sites would severely reduce the impact of precision treatments.

Avena, softchess (Bromus hordeaceus) and Vulpia sp. had a clear early phenology (Figure 7), and all plants had already set seed by May 12, 2008. Conversely, barbed goatgrass, medusahead and annual ryegrass still had a significant proportion of vegetative tillers on May 18, 2008. Two results were remarkable (Figure 8). First, annual ryegrass did not mature as early as expected; it was similar to the “late” species. Second, ryegrass, medusahead and barbed goatgrass exhibited a bimodal distribution of phenological stages late in the season. Because the ultimate fate of the tillers ranked was not determined (sampling was destructive), we cannot be sure that tillers in the left “hump” of the distribution would have produced seed. These results indicate that the phenological stages of annual grasses in California are more complex than we originally expected, and that it deserves more careful study and monitoring. It is imperative to assess the potential effects that climate change can have on the interaction between noxious invasive grasses, desirable exotic grasses, forbs and prevailing grazing management.

Precision grazing to control medusahead.

Precision grazing at Antibodies site.

Pastures treated with precision grazing in 2007 were measured again in 2008 to determine the ultimate effectiveness of treatments in reducing medusahead reproduction and populations. The treatments obtained were as described in Table 6. Stocking rates applied ranged from 2.6 to 5.2 AUM/ha. These stocking rates were achieved in one-two weeks by having very high stocking densities.

Statistical analyses detected no differences among treatments; regardless of the duration or level of utilization obtained. This means that even the treatments with the lowest stocking density and longest grazing duration achieved levels of control similar to those of higher stocking densities. Precision grazing was very effective in controlling medusahead. Both in 2007 and 2008, medusahead seed production in areas treated with precision high-intensity grazing was less than 1/4 of seed production in areas grazed under the normal management (Figure 10). This indicates that medusahead did not recover on the season following treatment.

Grazing treatments not only reduced medusahead seed production but also reduced its cover in 2008. The reduced cover by medusahead resulted in less area covered by thatch, more area covered by other species and more bare ground. The increase in bare ground is a potentially negative effect of the high grazing intensity. The persistence of this and its consequences should be checked before the high intensity grazing can be prescribed without reserve.

The heavy grazing did not affect seed production by other species as much as it affected the target weed. This was expected because of the precision treatment timing relative to phenology. Although not significantly different, seed production of non-target species tended to be a bit lower in treated than non-treated areas. The composition of the grazed areas changed to be dominated by softchess (Bromus hordeaceous) and filaree (Erodium botrys), which are good forage species.

Precision grazing at OWNS site.

Seed production by medusahead was significantly reduced by all grazing treatments relative to the ungrazed control (Figure 14). No differences were detected among grazing treatments, indicating that all treatments were similarly successful in reducing medusahead fecundity. Relative cover of Mh at the end of the season one year after grazing was applied (Figure 15) was significantly lower in grazed areas than in exclosures. However, pattern and level of relative Mh cover after grazing was applied were similar to those prior to grazing (Figure 16). This may indicate that the control plots where grazing was excluded for a season may have promoted medusahead, and that the regular grazing was sufficient to keep medusahead at a lower density.

When seed production of medusahead is expressed as a proportion of all seeds produced per unit area (Figure 17) the differences between control and treatment become non-significant. It appears that grazing reduced fecundity of desirable and other species as well as of Mh. These results indicate that temporally precise grazing at the stocking densities and rates applied were not clearly effective to control Mh. Whereas grazing with sheep at stocking rate of 1-2 AUM/ac (2.6-5.2 AUM/ha) was effective at the Antibodies site, grazing with cattle at stocking rates below 0.9 AUM and effected during longer periods with lower stocking density was not completely effective at the OWNS site. This experiment and a second experiment with sheep (not reported here) indicate that the lowest stocking rate applied during one-three weeks has to be above ~ 1.0 AUM/ac (>2.2 AUM/ha). This requires stocking densities above 2-3 AU/ac.

Although medusahead was apparently not selectively reduced, the potentially dramatic effect of precision grazing was observed in the field (Figure 18). The right side of the figure is pasture 6, which received a stocking rate of 0.66 AUM/ac obtained by grazing three yearlings for 21 days in a 1.84 ac (0.75 ha) pasture. The left side is pasture 7, which had 0.95 AUM/ac (11 yearlings during 14 days in 3.66 ac). The photo, taken in 2009 one year after the application of precision grazing, shows greater density of Avena and more residual herbage mass in pasture 6.

Effect of low-moisture supplement to promote grazing of medusahead.

Supplement attracted cattle to graze more near the supplement tubs (Figure 20). The increased grazing pressure resulted in some reduction in Mh cover (Figure 19), but it also created areas of high impact within a 5 m radius of the supplement tubs.

Differences in medusahead cover between inside and outside of the exclosures indicated that exclosures themselves acted as attractants because animals used them as scratchposts. Areas around exclosures were heavily trampled both in the control and supplemented areas. This resulted in a confounding of the effect of exclosures and supplement as attractants. Because of this confounding, results from “control” areas were not used. Regardless of this confounding, areas along transects in the supplemented areas exhibited the lowest proportion of medusahead.

In the patches that received supplementation animals tended to establish trails and areas around the supplement containers that were excessively trampled and could become starting points for water erosion in slopes. Therefore, this management tool has to be applied carefully and with appropriate monitoring to prevent soil degradation.

Effect of timing and intensity of clipping on medusahead and goatgrass.

Compared to undefoliated treatments, defoliation of both medusahead and goatgrass at any stage of growth from V3 (late vegetative stage) through R7 (kernel elongation) or R8 (milk stage) significantly reduced plant height and seedhead density (p < 0.05 in all cases; Figure 21). For both species, the canopy height and seedhead density generally decreased as defoliation height decreased and as defoliation was applied at later phenological stages.

Although these grasses produced some re-growth after defoliation prior to the R5 stage, defoliation at the 3 cm height eliminated medusahead seed production at all dates from V3 through R7 stages (Figure 21). Defoliation at 6 cm height also eliminated medusahead seed production at all dates from R4 through R7 stages. Defoliation of medusahead at 9 cm height did not consistently eliminate medusahead seed production prior to the R5 growth stage, and at some of these dates resulted in seed density as high as 25% of the undefoliated control. Therefore, we recommend defoliating medusahead at heights between 3 and 6 cm during either the R4 or R5 stage.

Barbed goatgrass continued to grow after defoliation later into the season. Seed density of Gg was also less affected by defoliation than Mh, and it did not exhibit an interactions between intensity and timing of defoliation (Figure 23). Defoliation at the 3 or 6 cm height at the R4 through R8 stages reduced barbed goatgrass seed production by 95% or more. However, barbed goatgrass seed production could not be consistently eliminated by clipping before or on the R5 growth stage. Although it was completely eliminated by defoliating at 6 cm at the R5 stage, seed production did occur in treatments with defoliation at the 3 and 9 cm heights. At any height from 3 to 9 cm, defoliation of barbed goatgrass prior to the R5 stage also resulted in re-growth capable of producing seeds. As with medusahead, we recommend defoliating goatgrass at heights between 3 and 6 cm during either the R4 or R5 stage.

The results of our research show that mechanical defoliation can be an effective method for the elimination of medusahead seed production. Mechanical defoliation can also greatly reduce, but not completely eliminate, barbed goatgrass seed production. The best time for defoliation is at the phenological stage R4 (emergence of awns) or R5 (visible anthers), which can avoid the problem of dropped spikes germinating in the following year. Our results confirm the point that the optimum time for mowing to control most annual species is in the flowering stage before seed development (DiTomaso 2000). At this time, medusahead is at a phenological stage that is at least a month later than most annual species (Dahl and Tisdale 1975; Young et al. 1970). Moreover, desirable forage species such as soft brome and clover have almost finished their life cycle. The defoliation causes little if any damage to the reproduction of native, desirable species and can reduce medusahead and barbed goatgrass by almost 100% with a single defoliation event. This invasive control method is more effective than repeated mowing that can favor low-growing weeds or damage desirable native species (Ashton and Monaco 1991). Based on our short-term results, we can provisionally recommend a defoliation height of 3-6 cm to control invasive medusahead and barbed goatgrass. However, further research on the impacts of mechanical defoliation on botanical composition in the following year is needed to better understand the long-term effects of this control strategy.

Large-scale mowing to control medusahead.

Medusahead cover ranged from 47 ± 5.4 to 23 ± 4.6 %. The other main species present were Torilis sp., Trifolium hirtum, Vicia sp., Bromus hordeaceus and Avena barbata. Several swaths were mowed across transects on 7 May 2007. Preliminary measurements taken on June 4, 2007 indicated that medusahead seed production in mowed and control areas were 140 ± 35 and 3030 ± 900 seeds m-2 at the end of the season when mowing took place.

Transects were measured again on May 8-9, 2008 and photos were taken of twenty 0.5 x 0.5 quadrats spaced every 5 m in each transect. The impact of mowing on medusahead was visually obvious (Figure 24). The rancher reported that sheep and cattle concentrated on the mowed areas because there was a greater availability of palatable species without the medusahead thatch. Results were so positive that the rancher decided to double the area mowed (Figure 25).

Application of glyphosate.

As expected, the early- and mid-applications killed all vegetation and produced little forage. A later application significantly reduced medusahead without obliterating the season’s forage. Cost of application of herbicide was $15/ac, including labor, fuel, herbicide and machinery.

There were no effects of dose or date of application on the degree of control. All treated areas had similar proportions of medusahead in the seedling stage (Figure 26). At the beginning of the season following the application of herbicide (2008), treated plots had significantly lower proportion of Mh than control plots. In the following season (2009), both treated and control areas had a lower proportion of Mh than controls in the first season. This decline in the number of Mh plants in the control areas may be related to the general reduction in Mh density achieved in the whole experimental area, which probably resulted in fewer seed reaching both treated and untreated areas.

The early application of herbicide resulted in a significantly lower forage production that in the control (Figure 27). Herbicide application in the other two dates did not affect forage production relative to their controls. Forage production in the following year tended to be greater in treated plots and was significantly greater in the plots treated early. This was an unexpected result and may have been due to a compensatory or renewal effect of the complete vegetation removal caused by the early application. Given that control areas were bands in side the treated plots, it is likely that the early application removed competition and released resources to those plants in the control band.

Comparative nutritional quality of medusahead and goatgrass.

Patterns of gas production were different among species and phenological stages. Both medusahead and goatgrass had slower rate of gas production than ryegrass and alfalfa within the first eight hours (Figure 28). Whereas goatgrass has a relatively high degradability in stages V2-R4, medusahead is clearly slower than the rest of the species (Figure 29).

Although goatgrass and medusahead differed in gas production, their crude protein content was not significantly different. The percentage of crude protein dropped drastically in both grasses as they entered the reproductive phase (Figure 30). In stages beyond R5, the forage is not suitable even for dry mature cows, except for a few months in the middle of pregnancy.

The increase of fiber (ADF) concentration with maturity is much steeper in goatgrass than medusahead (Figure 31). This explains the rapid decline in fermentability in goatgrass relative to Mh. Medusahead is known to have high concentration of silica. We determined that in our samples it had about 2.5% of silicon, whereas goatgrass had 1.7% Si. The concentration of Si did not change with phenology and was always high for medusahead (Figure 32).

In addition to having poor nutritional composition, both species are intensely avoided by grazer, particularly after the awns emerge from the sheath of the flag leaf. At that stage, the awns are still soft and cannot cause much harm, but they must give an unpleasant feel that makes them rejected. Thus, the impact of these weeds on forage value cannot be evaluated only on the basis of chemical composition, but must include a behavioral component.

Medusahead germination and interference.

Eighty percent of Mh seeds germinated four days after the start of the experiment, and 99% germinated by the end of Experiment 1. Rose clover germination was too low in all treatments, including the control, to be analyzed. Clover data were discarded. Germination results for the five remaining species are shown in Figure 33. Germination of all species was significantly delayed by at least one Mh plant part.

Like in Experiment 1, 80% of Mh seeds germinated by the fourth day of experiment 2. Germination results are shown in Figure 34. Seed germination of Mediterranean barley (Hordeum), wild oats, ryegrass and soft chess was significantly delayed when sown in Petri dishes where Mh seeds had germinated and awns had been soaked. Notably, there was no significant effect of residual chemicals on seed germination and growth in purple needlegrass. In both experiments, time to germination was affected by species, Mh plant part, and the interaction of these two factors (p < 0.001). The presence of Mh tissue or germinating seeds generally slowed germination of all species. Overall, germination was slower in Experiment 2. Species that germinated faster tended to exhibit greater impacts of Mh treatments.

There was a linear effect (P<0.01) of number of Mh seeds on germination of target species in experiment 1 and a quadratic effect in experiment 2. This was a “dose response” whereby increasing number of Mh seeds reduced germination rate, except for purple needlegrass. Experiment 1 (P=0.10) and experiment 2 (P<0.001) exhibited an interaction between species and “dose” indicating that the effect of number of seeds depended on the target species. Hordeum was very susceptible to dose; Avena, Brho and Lomu were intermediate; and Napu was resistant. Thus, the second experiment supported and augmented the results from Experiment 1. Overall, the impacts of Mh seed “dose” were greater in Experiment 2 than in Experiment 1, a fact that is consistent with the placement of target seeds on the same place where Mh seeds germinated, and therefore, where target seeds were exposed to greater concentration of the intervening compounds.

Germination of purple needlegrass was slowed down by the presence of previous season’s Mh culms and seedhead “skeletons” consisting of the remains of the spike after florets have disarticulated. After four-eight days of germination time, the total number of seeds germinated in the treatments with awns or culms, and old inflorescences was about half of that observed for controls.

All treatments with some medusahead tissue resulted in significantly less seedling mass than the control. The difference in mass reflects the combined effects of delayed germination and growth rate, if any. Since we did not measure growth rate, we cannot know if it was affected directly by the presence of Mh.

Our results support the hypothesis that medusahead has allelopathic effects that inhibit the germination and growth of competitors in California’s annual grasslands. We observed that the presence of several Mh tissues delayed germination of annual grasses by two-five days, when seeds were germinated at room temperature on saturated paper in Petri dishes. Wild oats was the species most significantly inhibited, with germination delays lasting up to several days. However, overall allelopathic interference from Mh appears to operate primarily in the first few days of seed germination, providing Mh a short window of time, or head-start, in which to germinate, grow, and establish before its surrounding competitors.

If allelopathy by Mh is corroborated in further research, this will constitute a significant piece of information to plan management strategies. Allelopathy may delay the other species even before Mh germinates or grows. If the chemical interaction is mediated strongly by the dead tissues from previous seasons, Mh’s negative impacts could be perpetuated even after its reproduction is prevented. Future studies are also needed to elucidate species-specific responses to Mh allelopathy. Identification of species that are relatively resistant to Mh allelopathy will be invaluable to designing more effective control strategies.

Literature Cited

Bastow, J.L., E.L. Preisser, and D.R. Strong. 2008. Holcus lanatus invasion slows decomposition through its interaction with a macroinvertebrate detritivore, Porcellio scaber. Biological Invasions 10:191-199.


Bovey, RW, D LeTourneau, & LC Erickson. 1960. The chemical composition of medusahead and downy brome. Weeds 9(2): 307-311.

California Department of Food and Agriculture, Plant Health and Pest Prevention Services,, verified February 11, 2011

Coleman, H.M., and J.M. Levine. 2007. Mechanisms underlying the impacts of exotic annual grasses in a coastal California meadow. Biological Invasions 9:65-71.

Dahl, B.E. and E.W. Tisdale. 1975. Environmental factors relating to medusahead distribution. Journal of Range Management 28:463-468.

DiTomaso, J.M. 2000. Invasive weeds in rangelands: species, impacts and management. Weed Science 48:255-265.

DiTomaso, J.M., K.L. Heise, G.B. Kyser, A. M. Merenlender, and R. J. Keiffer. 2001. Carefully timed burning can control barb goatgrass. California Agriculture 55(6):47-53

DiTomaso, J.M. and E.A. Healy, 2007. Weeds of California and Other Western States. University of California, Agriculture and Natural Resources, Publication 3488, Vol. 2, p. 1013.

Harris, G.A. and C.J. Goebel, C.J. 1976. Factors of plant competition in seeding pacific northwest bunchgrass ranges, College of Agric. Rsh. Ctr. Bull. 820, Washington State Univ, Pullman, WA (1976), p. 22.

Jacobsen, W.C. 1929. Goatgrass-a weed pest of the range. The Monthly Bulletin. Department of Agriculture, State of California 18:37-41.

Jensen, K., and K. Gutekunst. 2003. Effects of litter on establishment of grassland plant species: the role of seed size and successional status. Basic and Applied Ecology 4:579-587.

Kennedy, P. B. 1928. Goatgrass or wild wheat (Aegilops triuncialis), J. of the Am. Soc. Of Agron. 20:1292-1296.

Kyser, G.B., J.M. DiTomaso, M.P. Doran, S.B. Orloff, R.G. Wilson, D.L. Lancaster, D.F. Lile, and M.L. Porath. 2007. Control of medusahead (Taeniatherum caput-medusae) and other annual grasses with imazapic. Weed Technology 21:66-75.

Miller, H.C., D.W. Clausnitzer, and M.M. Borman. 1999. Medusahead, In R. L. Sheley and J. K. Petroff, eds. Biology and Management of Noxious Rangeland Weeds. Oregon State University Press, Corvallis.

Monaco, T.A., T.M. Osmond, and S.A. Dewey. 2005. Medusahead control with fall- and spring-applied herbicides on northern Utah foothills. Weed Technology 19:653-658.

NOAA. 2009. Online Climate Data Directory. Last accessed 4 January 2009.

Northam, F.E., R.H. Callihan, and M.M. Puchalski. 1996. Coleorhizal hairs in germinating medusahead (Taeniatherum caput-medusae). Weed Science 44:884-889.

Olson, B.E., and R.T. Wallander. 2002. Effects of invasive forb litter on seed germination, seedling growth and survival. Basic and Applied Ecology 3:309-317.

Oregon Dept. of Agriculture Noxious Weed Control Program. Noxious Weed Policy and Classification System. Feb. 2007 (, verified Feb. 11, 2011.

Pimentel, D. 2005. Environmental consequences and economic costs of alien species. Invasive Plants: Ecological and Agricultural Aspects:269-276.

Peters, A., D.E. Johnson and M.R. George. 1996. Barbed goatgrass: a threat to California rangelands. Rangelands 18 (1), February 1996. pp. 8-10.

Rotundo, J.L., and M.R. Aguiar. 2005. Litter effects on plant regeneration in arid lands: a complex balance between seed retention, seed longevity and soil-seed contact. Journal of Ecology 93:829-838
Talbot, M.W. and L.S. Smith. 1930. The goatgrass situation in California. The Monthly Bulletin, Dept. of Agriculture, State of California 19(1): 40-46.

Weed Science: Principles and Practices (3rd Edition), F.M. Ashton & T.J. Monaco. New York: John Wiley & Sons (1991). ISBN 0 471 60084 9.

Young, J.A., R.A. Evans, R.O. Gifford, and R.E. Eckert. 1968. GERMINATION OF MEDUSAHEAD IN RESPONSE TO OSMOTIC STRESS. Weed Science 16:364-&.

Young, J.A., R.A. Evans, and B.L. Kay. 1970. PHENOLOGY OF REPRODUCTION OF MEDUSAHEAD. Weed Science 18:451-&.

Young, J.A. 1992. Ecology and management of medusahead (Taeniatherum caput-medusae ssp asperum [Simk] Melderis). Great Basin Naturalist 52:245-252.

Research conclusions:

This project benefits producers the general public in several ways. First, we increased awareness about the invasive species problem. Producers, agency personnel and consultants, as well as team members, became familiar with the phenology and growth stages of medusahead. For example, they learned that medusahead seed disperses in late summer, so attempts to control it with fire in fall are not very successful because seeds are already in the ground where fire temperatures are not sufficient to kill the seeds.

We applied grazing treatments in several ranches, with impact on several hundred acres. We have formed an effective group where we shared information relevant to invasive species control and other rangeland management issues. We communicate by electronic mail and an internal wiki site that was created for the group. The linkages and communications established have been useful to disseminate the experience of individuals to the whole group.

Many stakeholders and members of the urban public learned to recognize medusahead and other invasive species. Four high school students and seven undergraduate students participated in this project and became familiar with the issue of invasive species and the importance of rangelands. High school students made presentations to peers and their families, thus extending the knowledge to an audience that would otherwise never come into contact with this type of imformation. This knowledge greatly increased their awareness about the many challenges posed by the increase in invasive species in California and in the U.S. in general. Many individuals expressed surprise at the abundance of invasive rangeland weeds once they were able to recognize them.

The impact of this project is significant in terms of the variety and number of people who have received information directly. We estimate that we have reached more than 400 individuals directly through field days, presentations, visits to ranches and scientific meetings. Many of these individuals are extension agents and participate in Regional Conservation Districts and Weed Management Areas, as well as in federal and non-government agencies, and will certainly continue to multiply the reach of our results. Our members have received invitations from other land management organizations to present results. Overall, we have been very effective at communicating within our large group and with the broader clientele.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

Laca, E. A. 2009. New approaches and tools for grazing management. Rangeland Ecology and Management. Rangeland Ecology and Management 62:407-417.

Laca, E.A. 2009. Precision livestock production: tools and concepts. R. Bras. Zootec., v.38, p.123-132, 2009 (supl.).

Davy, J.S., E.A. Laca, L.C. Forero. “Medusahead: What is being tested to reduce it?” Northern California Ranch Update. Vol. 3, Issue 1, March 2009.

Coatney, Kathy. “Reserachers look at new ways to control medusahead.” California Farm Bureau Federation: Ag Alert. 24 September 2008.

Hagg, Ed. “Grazing to Greener Pastures.” ANGUS Journal, April 2008, pp. 156-159.
Presentations, Posters and Abstracts

Zhang, J., M.W. Demment, C. Schriefer, C. Cherr and E.A. Laca. 2010. Control of medusahead (Taeniatherum caput-medusae) and barbed goatgrass (Aegilops triuncialis) with precision defoliation. Weed Science Society of America Annual Meeting, Denver, Colorado, Feb 7-11 2010.

Zhang, J., M.W. Demment, C. Schriefer, M.B. McEachern and E.A. Laca. 2010. Evidence for allelopathic interference in an exotic invasive grass, medusahead (Taeniatherum caput-medusae). Weed Science Society of America Annual Meeting, Denver, Colorado, Feb 7-11 2010.
Cherr, C. and E. A. Laca. “Medusahead distribution provides insight on invasion causes and risk.” Yolo County Resource Conservation District Meeting, 8 January 2009.

Barry, S. and Larson, S. Rangeland Weed Workshop, Concord, CA. March 18, 2008.

Becchetti, T., C. Schriefer, J. Zhang, C. Cherr, J. Harper, M. Doran, S., Larson-Praplan, S. Barry, J. Davy, R. Larsen, L. Forero and E.A. Laca. “Controlling Medusahead – Identifying the Period of Susceptibility.” January 2008. 61st Society for Range Management Annual Meeting, Paper No. 2339-1.

Becchetti, T., S. Larson-Praplan, J. Zhang, C. Dillard, C. Schriefer, C. Cherr, E.A. Laca. “Ecological and Economical Impacts of Management Options for Medusahead Control.” January 2009. 62nd Society for Range Management Annual Meeting, Paper No. 20-10.

Cherr, C., E.A. Laca. “Spatial Distribution and Scaling of Impacts of Invasive Grasses.” January 2009. 62nd Society for Range Management Annual Meeting. Paper No. 20-13.

Davy, J. "Partnering to Control Weeds Panel", Weed Management Areas Statewide Meeting. Woodland, CA. 10 February 2009.

Davy, J. "Techniques for rangeland weed control and tour", Glenn/Colusa Cattlemen's Spring Field Day, Williams, CA. 24 April 2008.

Davy, J. “Building a tool chest to control medusahead,” Tehama County Cattlemen’s Spring Field Day, Red Bluff, CA. 29 March 2008.

Laca, E.A. “Grazing management to control invasive weeds,” UCCE Grazing Management Workshop, Woodland, CA. 28 August 2008.

Laca, E.A. “Medusahead biology as the basis for its control.” 52nd Annual Weed Day, UC Davis, Davis, CA. 17 July 2008.

Laca, E.A. “Controlling Medusahead” – Emilio A. Laca, Oakdale Livestock Forum, Oakdale, CA. 4 March 4, 2008 (55-60 people).

Laca, E.A. and Cherr, C. “Spatial Distribution and Scaling of Impacts of Invasive Grasses,” Albuquerque, NM. Society for Range Management 62nd Annual Meeting. 8-12 Febuary 2009.

Larson-Praplan, S., J. Harper, T. Becchetti, M. Doran, S. Barry, J. Davy, C. Cherr, C. Schriefer, J. Zhang, E.A. Laca. “Grazing Strategies to Control Medusahead on California Rangelands.” January 2008. 61st Society for Range Management Annual Meeting, Paper No. 2288-1

Barry, S. and Larson, S. Rangeland Weed Workshop, Concord, CA. March 18, 2008. 105 landowners in attendance.

Field Demonstrations
Presentations by Corey Cherr, Morgan Doran, and Emilio A. Laca. Multiple approaches to control medusahead: Mowing (Dunnigan Hills), precision grazing (Antibodies site), and herbicide (Dunnigan Hills site). 15 October 2008. 18 landowners and stakeholders attended.

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

This project clearly shows that medusahead density can be reduced significantly in just one season if its seed production is prevented by defoliation, mowing or herbicide application after the boot stage and before the grain fills the full length of the lemma. The elusive key is to achieve uniform levels of defoliation or medusahead plant death within the narrow two-three week window without jeopardizing desirable species or causing soil degradation.

In order to plan for such precise timing of applications, one needs accurate forecasts of medusahead phenology. Our attempts indicate that there are significant difference in phenology over regions, but we were unable to determine the main causal factors determining the timing of the reproductive phase in medusahead. More research is needed with more intensive temporal sampling to determine how medusahead's phenological "clock" is set.

Based on the typical stocking rates in California, and on the stocking densities necessary to achieve medusahead control, we estimate that ranches should be able to apply precision grazing to a maximum of 1-5% of their land per year. The long term effectiveness of the method depends on the rate at which medusahead can expand again after treatments. Rates of medusahead expansion should be looked into.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.