Grazing Strategies to Control Medusahead in California

2008 Annual 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:

Grazing Strategies to Control Medusahead in California


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. Susceptible phenological stages are predictable but vary over regions. Low-moisture supplement placed in medusahead patches increases grazing intensity, but the effect is localized. Results and approaches were disseminated in several regional and national meetings, and by direct communication with producers. 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. Progress was better than satisfactory.

Objectives/Performance Targets

Medusahead (Mh), an invasive noxious 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 key detriment of 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. In the western US, 62 million ac are at risk of Mh invasion, which results in a loss of $20/ac/yr in grazing capacity.
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.


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

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 medusahead infestations.

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

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

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.

Precision grazing with sheep to control medusahead
Medusahead response one year after precision grazing

Pastures treated with precision grazing in 2007 were measured in 2008 to determine the ultimate effectiveness of treatments in reducing medusahead reproduction and populations. 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 ¼ of seed production in areas grazed under the normal management. This indicates that medusahead did not recover at least until the second season. 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.

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.

Effect of pasture size and grazing duration on medusahead control

Results from the grazing experiment done in 2007 showed that all treatments had been successful. Treatments in 2007 involved small pastures and short grazing durations with very high stocking densities. Those conditions are difficult to achieve in commercial operations because of the costs associated with fencing and the large numbers of animals required. Thus, we designed a new grazing experiment with larger pastures, longer grazing periods and lower stocking densities.

The study area consisted of a 25-ha pasture in Yolo County, CA. The site is normally grazed by 100 Dorset and Suffolk ewes from November through May. Sheep receive alfalfa hay as supplemental feed. We used combinations of high and low animal density with short and long grazing periods to obtain a series of levels of utilization. The treatments applied in 2008 involved lower animal densities, longer grazing periods and larger pastures than those applied in 2007. This experiment was conducted in an area that was adjacent but did not overlap with the area used in 2007.

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 or when the animals had to be removed for breeding.

Herbage botanical composition, mass, and nutritional quality were measured before grazing and after animals were removed from each plot. Additional measurements were completed the end of the growing season in 2008 to determine seed production by medusahead and other grasses. Botanical composition by species was assessed visually. 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. In general, all measurement methods were the same as in 2007. Results for this experiment will not be meaningful until the end of the current growing season of 2009. We will measure medusahead mass, cover and seed production in all plots to determine the final treatment effects.

Precision grazing with cattle: Owens 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. Treatments were combinations of high and low animal density with short and long grazing periods to obtain a series of levels of utilization.

Herbage botanical composition and Mh/goatgrass/star thistle phenology and coverage surveys were completed before grazing and after animals were removed from each plots. Botanical composition by species was assessed visually. 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 of 2008.

Pastures were about 50 m wide and 150 to 200 m long and oriented such that one end was at a riparian area with a watering point and the other end was near the top of a rocky hill. This layout maximized the opportunity for animals to impose a gradient of utilization with the highest impact near the watering point and the least impact on the hill. Because of this, the results obtained should be comparable to what would take place in much larger pastures with more even dimensions.

Preliminary results and visual inspection indicate that indeed animals imposed a significant gradient of utilization. Areas with high levels of use appear to have less medusahead. Pastures had large patches of starthistle established in patches of deep heavy clay soil. Although cattle grazed the thistle heavily, it grew back after animals were removed. Thistle has a phenology that is later than medusahead, it can resprout after grazing, and it can grow and reproduce in late spring and summer after livestock have been moved to summer pastures. This raises the potential for promoting thistle by removing competition by medusaehad. The interaction between medusahead control and starthistle has to be explored further before precision grazing can be recommended for lands where these two weeds coexist.

Effect of mowing on medusahead reproduction and density

Medusahead has invaded a large proportion of the Dunnigan Hills region of Yolo County, California. 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, to the point that in some patches medusahead thatch has accumulated to the point that it smothers itself. One rancher contacted our group for advice about mowing and we established a trial to determine the effectiveness of mowing with commercial machinery.

In 2008 we established new mowed areas and measured the impact of mowing conducted in 2007. We established five transects in the areas mowed and determined botanical composition prior to mowing by visual estimation of cover. Medusahead cover ranged from 47 ± 5.4 to 23 ± 4.6 %. The other main species were Torilis sp., Trifolium hirtum, Vicia sp., Bromus hordeaceus and Avena barbata. Several swaths were mowed across the transects on 7 May 2007. Preliminary measurements taken on 4 June 2007 indicated that meduashead 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 8-9 May 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. 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.

Low-moisture blocks to promote grazing of medusahead

We trained livestock to find and consume a highly palatable low-moisture supplement offered in barrels marked with flags early in the spring at the Cook, Gonsalves, Bradford, Gallatin, Sonoma Land Trust and Dolcini ranches. Supplement was placed in areas of high medusahead density to attract livestock. A series of transects with grazing exclosures were established centered at the supplementation site and at a similar medusahead patch at least 300 m away from the supplement. We measured botanical composition, degree of grazing, and herbage height prior and after grazing in the springs of 2006, 2007, and 2008.

Differences in medusahead cover between inside and outside of the exclosures indicate 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. Regardless of this confounding, areas along transects in the supplemented areas exhibited the lowest proportion of medusahead.

The effect of the attractants was more obvious on the total grazing intensity, which was calculated as a weighted average of areas ungrazed (0) or grazed with light (1), medium (2), or high intensity. 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.

Medusahead phenology

Phenological information about medusahead and associated species was collected in twelve sites in eleven counties during the growing seasons in 2006, 2007, and 2008. Data were been collated into a database where they were joined with topographical and weather data to develop predictive models for phenological stage as a function of date, biophysical site characteristics, location and weather.

Statistical models including all variables were tested and reduced by removing non-significant terms. While the modeling effort is not yet complete, a set of models was developed. Phenological stage was given a numerical value according to Table 4 and modeled as a sigmoidal 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.

Analyses indicate that there are significant regional differences in the phenology of medusahead. Whereas in Glenn and Stanislaus counties medusahead reached late vegetative state in 20 April 2006, that phenological stage was not reached until 8 May in Alameda and 4 May 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 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, and all plants had already set seed by 12 May 2008. Conversely, barbed goatgrass, medusahead, and annual ryegrass still had a significant proportion of vegetative tillers on 18 May 2008. Two results were remarkable. 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.

Forage Quality Assessment of Medusahead and Barbed Goat Grass

This experiment tests the digestibility of Mh and GG in comparison to rye grass and alfalfa in order to determine the amount of nutrition an animal may get from a given amount of these plants. Several 250 mg samples of medusahead, 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.

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 8 h. Whereas goatgrass has a relatively high degradability in stages V2-R4, medusahead is clearly slower than the rest of the species. 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. 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. 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.
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.

Evaluation of the economical impacts of management options for medusahead control

We conducted a preliminary evaluation of the economic impact of medusahead and various control treatments. The evaluation is based on the data we obtained as well as on subjective integration of field observations and discussions with ranchers.

Medusahead impact was estimated only on the basis of grazing capacity. This weed also reduces habitat value and other ecosystem services. Thus, our estimations are conservative. Based on field observations, sheep and cattle consume some medusahead (and goatgrass) before the onset of rapid spring growth, in early February. At best, the medusahead is consumed in the same proportion it is available during that time. From March until the beginning of the next season, both weed species and other forages that are within weed patches are avoided. About 1/3 of the total forage production grows before onset of rapid growth. Therefore, areas covered with medusahead lose at least 2/3 of the forage.

Based on a parallel project funded by Western SARE (GW07-006), we determined three classes of medusahead cover that can be identified and mapped at the state level using Landsat images. These classes are 40%. Based on the interspersion of weed and other forages, areas with less than 5% medusahead were considered to have full grazing capacity. Areas with 5-40% received a reduction of 50% grazing capacity, and areas with more than 40% medusahead cover received a reduction of 100% (these reductions are subjective estimates to get a general idea of the impact).

As an example, cost of weed impact was calculated as the cost of the grass hay necessary to compensate for the reductions due to weed invasion. Assuming a productivity of 1000 lb/ac of usable forage, an area with an intermediate level of medusahead cover would need 500 lb/ac of grass hay at a cost of $22.50/ac (no transportation cost was included). In areas with greater productivity, the loss or cost would be proportional to the productivity (for 1500 lb/ac cost would be $33.75/ac). Weed control methods can offset the costs of weed invasion. In a simplistic approach, any successful method that costs less than the weed impact could be applied for a net profit.

Supplementation. The supplement tubs did attract livestock, and we did see a small reduction in Mh cover. However, the supplementation appears to be effective within a radius of about 40 yards. Thus, frequent movement of the supplement is necessary. Labor costs were estimated at $10/ac based on how much time it took to look for Mh patches, to drive each week to and from the site, check and move the supplement. The cost of the supplement was not included as it is typically used anyway.

Mowing. Cost of mowing was estimated at $19/ac, including fuel, labor, and machinery.

Herbicide. Glyphosate was applied at 16 and 32 oz. per acre in a 1% water solution early, mid, and late season. 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.

All methods had a cost per acre lower than the forage loss caused by the weed. This is a conservative estimate because the benefits of one treatment or application, particularly of mowing or herbicide, will last at least 2 years and very likely 3 and more. We are currently monitoring the degree of reinfestation in the third year after control.


This project benefits producers and 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 in several hundred acres. We have formed an effective group where we share 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. This knowledge greatly increased their awareness about the many challenges posed by the increase in invasive species in California and in the US 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 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 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.

Impacts and Contributions/Outcomes

Laca, E. A. 2009. New approaches and tools for grazing management. Rangeland Ecology and Management. In Press.

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

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.

The following work still needs to be completed:

1.Add information to the new web sites for California Rangelands and Weed Research at UC Davis.

2.Conduct measurements, sampling, laboratory and statistical analyses for the grazing experiments conducted at Glenn and Yolo counties during the growing season of 2008. The effects of grazing treatments on medusahead populations will not be measureable until the end of the growing season of 2009.

3.Incorporate data from 2008 into phenology model to determine timing of grazing to control medusahead.

4.Publication of information in peer-reviewed journals.


Jim Yeager
34791 Creeks Edge Road
Davis, CA 95616
Office Phone: 5307562423