EFFECTS OF MULTI-SPECIES GRAZING ON LEAFY SPURGE (Euphorbia esula L

EFFECTS OF MULTI-SPECIES GRAZING ON LEAFY SPURGE (Euphorbia esula L.)

INFESTED RANGELAND USING ROTATIONAL GRAZING

(A Four-Year Summary)

¹Luke W. Samuel, ¹Kevin K. Sedivec, ²Timothy C. Faller,

²Jack D. Dahl, and ³Lyndon L. Johnson

¹Animal and Range Sciences Dept., North Dakota State University, Fargo, ND 58105.

²Hettinger Research Extension Center, Hettinger, ND 58639.

³USDA, Forest Service, Watford City, ND 58854.

Introduction

Leafy spurge is a plant widely dispersed across the northern hemisphere, including the United States and Canada, with a distribution center in the Caucasus Region of Asia (Croizat 1945 in Noble and MacIntyre 1979). This plant is found on every continent except Australia (Lacey et al. 1985). Leafy spurge is believed to have been introduced into mainland North America before 1872 (Callihan et al. 1991). Leafy spurge now infests thirty-nine states in the United States including every northern state and every Canadian province except Newfoundland (Lacey et al. 1985). One million hectares (two and a half million acres) in North America are infested by leafy spurge (Noble et al. 1979 in Noble and MacIntyre 1979), with an estimated 400,000 hectares (one million acres) in North Dakota (N.D. Dept. of Agriculture 1996).

Traditional approaches for controlling leafy spurge, e.g. herbicides, are becoming cost prohibitive as this noxious weed continues to spread. Many forms of biological and cultural controls have come into practice over the past twenty years. Grazing sheep on leafy spurge infested rangeland is one such cultural control. Cattle do not graze leafy spurge and often avoid leafy spurge-infested communities, creating opportunities for multi-species grazing with sheep. Multi-species grazing is the concurrent use of rangeland by more than one kind of animal, and this approach utilizes more than one class of vegetation (Merrill et al. 1966). Cattle and sheep grazing has the potential to reduce leafy spurge density, increase plant species richness, and improve the economic viability of a cattle operation on leafy spurge infested rangelands.

Research Objectives

The objectives of the study were to determine if simultaneous grazing of leafy spurge infested rangeland with cattle and sheep employing a twice-over-rotational grazing system in conjunction with biological control will (1) reduce leafy spurge density compared to season-long grazing and (2) enhance livestock grazing efficiency compared to season-long grazing.

Study Area and Design

This project was conducted on leafy spurge infested rangeland in western North Dakota from 1998 through 2001. The study area is located approximately ten kilometers (six miles) north of Sentinel Butte or 240 kilometers (150 miles) west of Bismarck, North Dakota. Two tracts of rangeland of 257 and 160 hectares (635 and 395 acres) comprise the replicated multi-species grazing trial in the Badlands vegetative region of North Dakota. Vegetation in this region is typical of northern mixed grass prairie and is classified as a wheatgrass-grama-needlegrass (Agropyron, Bouteloua, Stipa) plant community (Barker and Whitman 1989). Leafy spurge infested approximately forty to fifty percent of the land on these two study sites.

This trial was designed to test the effects of twice-over rotation (TOR) and season-long (SL) grazing on leafy spurge infested rangeland using multi-species grazing with cattle and sheep in combination with a biological control program. Each of two tracts of land were blocked into four cells with one cell randomly selected as SL treatment. The remaining three cells in each replicate were grazed using TOR grazing treatment. Two 0.40 hectare (one acre) exclosures were developed on each replicate by stratifying each treatment and randomly selecting points for development. The four exclosures, containing forty to fifty percent leafy spurge, were excluded from grazing and classified as biological control treatments.

Fifty permanent 100-meter line transects were systematically located in leafy spurge communities (26 transects) and native range (devoid of leafy spurge) vegetation sites (24 transects) throughout the replicates to monitor changes in leafy spurge stem density and plant species richness. Barbour et al. (1999) defined density as the number of plants rooted within each quadrat. Species richness is simply the number of species per unit area; diversity is a combination of richness and evenness, i.e., species richness weighted by species evenness (Barbour et al. 1999). Peet (1974 in Ludwig and Reynolds 1988) termed this "the dual concept of diversity," i.e., diversity combines species richness and relative species abundance.

Four transects were located in each cell of the TOR grazing treatments, eight transects in each SL treatment, and two in each of the biological control cells (0.40 hectare exclosures). In addition, two permanent line transects designed to monitor effects of leafy spurge on rangeland without grazing, biological, or other management were located in areas dominated by leafy spurge adjacent to each replicate.

Leafy spurge density and graminoid species frequency is collected every five meters using a 0.10 square meter frame and forb and shrub density and frequency is collected every five meters using a 0.25 square meter frame on the 100-meter line transects.

Livestock performance and production data is collected for cattle and sheep for determination of average daily weight gain and gain per area. Livestock are weighed at the beginning and end of each grazing season.

Treatment and year effects for leafy spurge stem density, and livestock performance were analyzed using a general linear model (GLM) (SPSS 1999). A mean separation was performed when significant (P<0.05) differences were found using Tukey’s Honesty Significant Difference (SPSS 1999).

Grazing Treatments and Grazing Plan

Cattle grazed each treatment from 1 June through 15 September while stocked in accordance with the recommended carrying capacity of the land as outlined in USDA Natural Resources Conservation Service technical guidelines (1984). Sheep grazed from 15 May through 15 September while stocked at forty percent of the original carrying capacity without adjustments to cattle numbers.

Carrying capacity of the TOR grazing treatment is 142.4 animal unit months (AUMs) and 73.6 AUMs on replicates #1 and #2, respectively. Stocking rates of the TOR grazing treatments were 0.28 AUMs/acre for both replicates #1 and #2. Type of cattle grazed is Angus-Hereford cross cow/calf pairs with cows weighing approximately 545 kilograms (1200 pounds). Thirty-six cow/calf pairs grazed replicate #1 and 18 cow/calf pairs grazed replicate #2. Since sheep will be stocked at forty percent of carrying capacity, sheep were grazed at 57.5 AUMs (replicate #1) and 33 AUMs (replicate #2) on the TOR grazing treatments. Type of sheep was mature white-faced ewes of which 86 head grazed on replicate #1 and 45 head grazed on replicate #2.

Carrying capacity of the SL grazing treatment was 39.6 and 33.9 AUMs on replicates #1 and #2, respectively. Stocking rates of the SL grazing treatments were 0.31 and 0.32 AUMs/acre on replicates #1 and #2, respectively. Type of cattle grazed is Angus-Hereford cross cow/calf pairs with cows weighing approximately 545 kilograms (1200 pounds). Ten cow/calf pairs grazed replicate #1 while 8 cow/calf pairs grazed replicate #2. Since sheep were stocked at forty percent of carrying capacity, sheep were grazed at 16 AUMs (replicate #1) and 15 AUMs (replicate #2) on the SL grazing treatments. Type of sheep grazed was mature white-faced ewes, with 23 head on replicate #1 and 20 head on replicate #2.

Livestock graze the SL treatment continuously throughout the grazing season. Livestock graze the TOR grazing treatment as one herd and rotate simultaneously. The entire herd of cattle and sheep graze one cell at a time, grazing forty percent of the available carrying capacity of the cell in the first rotation and sixty percent of available carrying capacity in the second rotation.

Results and Discussion

After four grazing seasons, leafy spurge stem densities were significantly (P<0.05) reduced on both grazing treatments and bio-control treatment on lowland and upland leafy spurge sites (Table 1 and 2). There were no (P>0.05) differences between the SL,TOR or non grazed bio-control leafy spurge treatments. The lowland sites on the TOR grazing treatment had the greatest decrease in leafy spurge stem densities at 80%. The SL treatment achieved the best control on upland sites with a decrease of 72%.

Table 1. Leafy spurge stem densities at lowland sites on the bio-control only, season long (SL) and twice-over-rotation (TOR) grazing treatments in 1998 and 2001.

Treatment¹

1998²

2001²

% Decrease from

1998 to 2001

# Stems/ 0.10 m²

Bio-Control

13.9 + 1.3^ax

3.1 + 0.6^ay

78%

Season-long

18.4 + 1.1^ax

6.7 + 1.2^ay

63%

Twice-over

18.2 + 0.8^ax

3.5 + 0.6^ay

80%

¹ Treatments with the same letter are not significantly different (P<0.05) (a, b, and c).

² Years with the same letter within each treatment are not significantly different (P<0.05) (x, y, and z).

Table 2. Leafy spurge stem densities at upland sites on the bio-control only, season long (SL) and twice-over-rotation (TOR) grazing treatments in 1998 and 2001.

Treatment¹

1998²

2001²

% Decrease from

1998 to 2001

# Stems/ 0.10 m²

Bio-Control

8.8 + 0.8^ax

3.3 + 0.6^ay

63%

Season-long

9.7 + 0.8^ax

2.7 + 0.4^az

72%

Twice-over

9.1 + 0.6^ax

3.0 + 0.3^ay

67%

¹ Treatments with the same letter are not significantly different (P<0.05) (a, b, and c).

² Years with the same letter within each treatment are not significantly different (P<0.05) (x, y, and z).

Cow average daily gain (ADG) was not (P>0.05) different between TOR and SL treatments during the four years of the study. However, cow ADG was lower (P<0.05) in 1999 compared to 1998, 2000 and 2001 on the TOR and SL treatments. Calf ADG also did not differ (P>0.05) between TOR and SL treatments for all four years. However, Calf ADG was lower (P<0.05) in 1998 then in 2000 on the SL treatment (Table 3).

There was no (P>0.05) difference in ewe ADG between TOR and SL treatments over the four years of the study. Ewe ADG was higher (P<0.05) on SL and TOR treatments in 1999 compared to 1998, 2000 and 2001. Ewe ADG on the TOR was also higher in 2001 than in 1998 (Table 4).

Table 3. Cow and calf average daily gains (ADG) for the season long (SL) and twice-over-rotation (TOR) treatments from 1998, 1999, 2000 and 2001.

Treatment

1998

1999

2000

2001

lb/day

Season-long Cows

1.13 + .12^ax

0.01 + .14^ay

1.21 + .13^ax

1.02 + .20^ax

Calves

2.23 + .08^axy

2.28 + .08^axy

2.43 + .06^ax

2.72 + .07^axz

Twice-over Cows

0.80 + .08^ax

0.07 + .07^ay

0.78 + .10^ax

1.15 + .20^ax

Calves

1.99 + .05^ax

2.19 + .07^axy

2.22 + .04^ay

2.46 + .05^az

¹ Treatments with the same letter, for the same class of livestock, are not significantly different (P>0.05) (a, b, and c).

² Years with the same letter, for the same class of livestock, within each treatment are not significantly different (P>0.05) (x, y, and z).

Table 4. Ewe average daily gains (ADG) for season long (SL) and twice-over-rotation (TOR) treatments during the 1998, 1999, and 2000 grazing seasons.

Treatment¹

1998²

1999²

2000²

2001²

lb/day

Season long

0.21 + .01^ax

0.35 + .02^ay

0.26 + .02^az

0.24 + .02^axz

Twice-over

0.20 + .003^ax

0.36 + .009^ay

0.25 + .01^axz

0.25 + .008^az

¹ Treatments with the same letter are not significantly different (P<0.05) (a, b, and c).

² Years with the same letter within each treatment are not significantly different (P<0.05) (x, y, and z).

Summary

The preliminary results from this trial are encouraging. The addition of sheep to a cattle only grazing operation was shown to effectively reduce leafy spurge stem densities. To date, both the SL and TOR treatments have performed well in the control of leafy spurge over the four years of the study, with both SL and TOR grazing treatments significantly reducing leafy spurge stem densities. However, the leafy spurge stem densities in the non grazed bio control exclosures were also reduced, and was not different than the reduction seen in the grazing treatments. This could be due to the fact that the bio-control exclosures were located inside the grazing study and comprised only 0.4% of the total area of the study, with the bio-control agents benefiting from the grazing treatments. Bio-control and grazing were both proven to be effective in reducing leafy spurge stem densities. However, the use of sheep as a long term management tool of leafy spurge without bio-control is still a proven method of control (Dahl et al. 2001) that allows producers to utilize available resources while providing added income. The use of bio-control does not provide the additional income that can accompany the production of sheep, but costs and labor factors may prevent the use of sheep as a control method. Multi-species grazing and bio-control both provide effective control of leafy spurge, and a land owner can implement a project using one or both techniques that best meets their needs.

Overall, cattle and sheep grazing simultaneously did not adversely affect the ADG of cows, calves, or ewes using either grazing treatment. Multi-species grazing is a good alternative for leafy spurge control while allowing for an increased carrying capacity of the land with no adverse affects on livestock performance.

Literature Cited

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NDSU Research Rpt. No. 111. Fargo.

Callihan, R.H., J.P. McCaffrey, and V.J. Parker-Clark. 1991. Leafy spurge:

biology and management. Univ. of Idaho College of Ag., Cooperative Ext.

System Ag. Exp. Sta. Current Information Series 877.

Dahl, J.D., K.K. Sedivec, T.C. Faller, D. Stecher, J.F. Karn, P.E. Nyren, and L. Samuel.

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rangeland (A five-year summary). N.D. State Univ. Ext. Service Sheep Day publication.

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