Introduction

Leafy spurge (Euphorbia esula L.) is an aggressive perennial herb that cattle and horses generally don't graze. If grazed by cattle or horses, it causes severe irritation of the mouth and digestive tract and even death. Cattle even avoid palatable grasses growing near this weed. It has reduced the carrying capacity of infested rangeland by 50 to 75 percent. Economic losses due to this weed in the western states is estimated to exceed $150 million annually.

Leafy spurge has taken over millions of acres of western grazing land. It is now well established in a few isolated sites in Klamath County, Oregon. Efforts to contain this weed are underway, but control options are costly and often ineffective.

Research from North Dakota indicates that 2,4-D, dicamba (Banvel), and picloram (Tordon 22K) are the most effective herbicides in controlling leafy spurge. Picloram is not used in Klamath County because it is too costly for widespread use, it is deadly to potatoes, which is a major crop in the county, and is very persistent in soils. The two remaining herbicides have proven less effective in controlling leafy spurge. The plant is resistant to chemical control due to extensive root systems. Roots may grow up to 15 feet deep and contain abundant nutrient reserves. These nutrient reserves enable the plant to recover from stress, including chemical control efforts. The depletion of nutrient reserves in the roots could greatly enhance herbicide effectiveness.

While cattle avoid leafy spurge, goats prefer it to grass and will consume large quantities of the weed. Regrowth following grazing utilizes root reserves and continued defoliation and regrowth will make the plant more susceptible to herbicide attack. Studies in North Dakota and Montana confirm the effectiveness of such integrated control efforts in those environments. Study is needed to document the efficacy of an integrated control program in southern Oregon.

Procedures

Plots were established in southern Klamath County on rangeland infested with leafy spurge. The study was arranged in a split plot design with four replications. The main plot was grazing treatments. Eight exclosures measuring 75 by 75 feet were constructed. Four exclosures were rotationally grazed by goats. Leafy spurge plants were severely defoliated three times during the growing season. Goats were added or subtracted as needed to adequately defoliate the leafy spurge without overgrazing the grasses in the exclosure. Grazing was excluded from the four remaining exclosures during the growing season. The area outside the exclosures was continuously grazed by goats at a stocking density of two goats per acre. Goats remained on the pasture through mid-August.

Herbicide treatments will be applied in the spring of 1998 prior to grazing by goats. Treatments will be applied in all three grazing treatments. Treatments will include an untreated control, 2,4-D, dicamba, and picloram at labeled rates. Leafy spurge plant densities will also be determined prior to herbicide application and in the spring.

Prior to the initiation of each rotational grazing cycle leafy spurge plant density, leafy spurge biomass, and grass biomass was determined using random samples measuring 0.25 m2. Rotationally grazed plots were sampled prior to grazing (Rotational-In) and after a two day grazing period (Rotational-Out). Leafy spurge leaves and stems were separated and percent leaf was determined. Exclosures were removed in the fall after goats were removed and the entire area was grazed by cattle to utilize the accumulated forage resource.

Protein concentration of leafy spurge roots is a good indicator of the relative health of the plant and can be used to evaluate the effectiveness of treatments in stressing leafy spurge. Roots will be collected from the top foot of soil for each treatment combination approximately April 1, prior to herbicide application. Total N will be determined using the near infrared reflectance spectroscopy calibrated by Kjeldahl analysis procedures.

Statistical analysis was performed using analysis of variance procedures.

Results

The goats were introduced to the leafy spurge infested pasture on June 1 and began to preferentially graze leafy spurge plants after two to three days. When introduced to a new feed source goats often require an adjustment period before they begin to actively feed on the new forage resource. Once the goats were accustomed to leafy spurge, the flock was introduced into the rotationally grazed paddocks. They were removed the evening of the second day of grazing. The goats readily consumed the leafy spurge in the rotationally grazed paddocks, leaving very few stems and almost no leaves (Table 1). Leafy spurge was consumed at a slower pace in the continuously grazed plots due to a more extensive area. However, by the second sample date leafy spurge biomass was reduced to one tenth the amount in ungrazed paddocks and significantly lower than rotationally grazed paddocks, which had experienced a substantial amount of regrowth (Table 1). When goats were reintroduced to the rotational plots following the second sample date they quickly brought leafy spurge biomass down to continuously grazed levels. A similar pattern was seen at the third sample date. Both continuous and rotational grazing eliminated leafy spurge seed production.

Leaf area was not measured, but percent leaf was determined and accurately reflects trends in photosynthetic area. Percent leaf following rotational grazing was very low. However, in the absence of goats, the plants quickly produced more leaves resulting higher percent leaves in rotationally grazed paddocks at the July 14 sample date (Table 1). Two days latter following grazing percent leaf of rotationally grazed paddocks were the lowest in the trial. In contrast, continuous grazing resulted in a slower decline of percent leaf with no recovery period. There was probably some replenishing of root reserves in rotationally grazed plants during the rest period between grazing. A more frequent grazing interval would result in less photosynthetic area for replenishing root reserves.

Grazing also affected leafy spurge density as expressed by stems per square meter. Rotational grazing decreased leafy spurge stem density to less than half pregrazing levels in only two days. Stem density of rotationally grazed paddocks did not increase during the rest period between grazing events. Stem density of continuously grazed paddocks were one fifth ungrazed levels and one half rotationally grazed levels at both the July 14 and August 19 sample dates.

Both grazing treatments resulted in greater accumulated grass biomass than the ungrazed control. At least twice as much grass was available for fall cattle grazing where goats had grazed. Residual grass biomass was slightly higher in continuously grazed paddocks than the rotationally grazed paddocks following the final grazing prior to goat removal.

It is clear that goat grazing reduced leafy spurge biomass, increased available grass biomass for fall grazing, and generally shifted the competitive advantage in favor of the grass species on the site. It is not known if continued goat grazing will significantly reduce the leafy spurge population in this environment. Further monitoring and study is needed to determine the long term effectiveness of goat grazing in reducing leafy spurge in southern Oregon pastures and rangelands. Application of chemical treatments and subsequent monitoring will also provide information on the efficacy of an integrated goat grazing - herbicide control program.