United States Department of Agriculture 

NATURAL RESOURCES CONSERVATION SERVICE 

Invasive Species Technical Note No. MT-4 

August 2006 

Integrating Herbicides and Re-vegetation on a Leafy Spurge Infested Pasture in the 

Bitterroot Valley, Montana 

by 

Jim Jacobs, NRCS Invasive Species Specialist 

Alan Knudsen, Missoula County Weed Management Coordinator 

Abstract 

Leafy spurge is one of the more problematic and economically significant noxious weeds in 

Montana because it reduces livestock forage and because herbicidal management is costly and 

short term. On a cattle ranch in south western Montana, picloram or imazapic (two herbicides 

used to control leafy spurge) were sprayed, and five competitive, forage grass species were 

seeded as monocultures in a controlled, replicated study to determine the effects of these 

treatments on leafy spurge suppression and grass establishment. Bluebunch wheatgrass, orchard 

grass, and thickspike wheatgrass established where herbicides suppressed leafy spurge density. 

Bluebunch wheatgrass and orchard grass reduced the biomass production of leafy spurge 

indicating competitive suppression of leafy spurge by these grasses. Results suggest that 

herbicides are necessary to establish grasses and to increase forage production on degraded 

pastures infested with leafy spurge. Regeneration of leafy spurge where grasses established 

indicates that control of leafy spurge by insect, goat, or sheep herbivory, and prescribed cattle 

grazing will be needed for sustainable management of leafy spurge. 

Introduction 

Leafy spurge (Euphorbia esula L.) has been reported in every county in Montana making it one 

of the more widespread noxious weeds in Montana. It infests an estimated three million acres in 

29 western states. On pasture and rangeland, livestock forage availability in leafy spurge 

infestations is reduced because leafy spurge suppresses the productivity of forage grasses and 

because cattle avoid grazing in leafy spurge infestations. On many infested pastures, perennial 

forage grasses have been replaced by leafy spurge and less palatable grasses such as bulbous 

bluegrass (Poa bulbosa L.), three-awn (Aristida purpurea Nutt.), and cheatgrass (Bromus 

tectorum L.). On these sites, controlling leafy spurge using herbicides, biological control insects, 

or grazing with sheep or goats may not restore forage quality or production. This technical note 

reports three years of data collected on a re-vegetation demonstration of a leafy spurge infested 

pasture in the Bitterroot Valley, Montana. 

Objectives 

The overall objectives of the study were to establish a demonstration of integrated management 

of leafy spurge that included herbicide, re-vegetation, biological, and grazing control methods, 

(Disclaimer: Any mention of products in this publication does not constitute a recommendation by the 

NRCS. It is a violation of Federal law to use herbicides in a manner inconsistent with their labeling.) 

NRCS−Montana−Technical Note−Invasive Species−MT-4 1
and to use re-vegetation and herbicides to improve forage production. Specific objectives were 

to determine the establishment success of grass species, their competition with leafy spurge, and 

herbicidal control of leafy spurge for grass establishment. 

Study Area 

The study area is located on a privately owned cattle ranch southeast of Lolo, Montana. The area 

is level and the long-term (30-year) average annual precipitation ranges from 15 to 19 inches 

(380 to 480 mm). The soils are classified as Bigarm gravely-loam (loamy-skeletal, mixed, frigid 

Typic Haploxerolls) 0 to 11 inches (0-280 mm) deep, 7 to 18 percent clay, 2 to 4 percent organic 

matter, and a pH range of 6.6 to 7.3. The historic habitat-type is classified as Festuca 

scabrella/Agropyron spicatum. The plant community composition at the start of the study in 

2002 was predominantly leafy spurge with Canada bluegrass (Poa compressa L.), cheatgrass, 

bulbous bluegrass, three awn, spotted knapweed (Centaurea maculosa Lam.), intermediate 

wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey], and bluebunch 

wheatgrass [Pseudoroegneria spicata (Prush) A. Löve]. 

Study Design 

The study was designed as a split-plot with six grass seeding treatments (including a no seeding 

control) as whole-plots and three herbicide treatments (including a no herbicide control) applied 

within the seeding treatments as sub-plots. Each grass seeding treatment plot was 14 by 45 feet 

divided into three 14 by 15 foot herbicide treatment plots. The herbicide treatments were 

randomized within each grass seeding treatment, and the grass seeding treatments were 

randomized within four replications on two sites. The study was first applied in 2002 and fenced 

with an eight-foot wildlife fence to exclude cattle and wildlife (fenced site). The study was 

repeated in 2003 on a second adjacent site but was not fenced (unfenced site). 

The six grass seeding treatments consisted of five grass species and a no seeding control. Grass 

species and seeding rates are listed in Table 1. All grass species are cool season, drought 

tolerant, long-lived perennial grasses that, with the exception of orchard grass, are native to 

North America. These species were chosen because they are adapted to the moisture and soil 

conditions of the site and because of their livestock forage value. 

The herbicide treatments included a no herbicide control, picloram applied at one quart 

product/acre (0.56 kg a.e./ha), and imazapic applied at ten-ounce product/acre (0.03 kg a.i./ha) in 

solution with one quart/acre methylated seed oil. The herbicides were applied in September 

before the first hard frost, which is one of the optimum times recommended for herbicidal 

control of leafy spurge. Grasses were seeded using a rangeland no-till drill on November 11, 

2002, in the fenced site and on October 27, 2003, in the unfenced site. 

NRCS−Montana−Technical Note−Invasive Species−MT-4 2
Table 1. The common and scientific names, seeding rates, and characteristics of the grass 

species seeded in the study. 

Common name Scientific name rate lb/acre Origin habit 

Bluebunch wheatgrass Pseudoroegneria spicata 10-14 Washington bunchgrass 

Big bluegrass Poa ampla 2-4 Oregon bunchgrass 

Great basin wild rye Leymus cinereus 6-11 Saskatchewan short rhizomes 

Orchard grass Dactylis glomerata 2-4 Turkey bunchgrass 

Thickspike wheatgrass Elymus lanceolatus 6-11 OR,WA,ID,CA rhizomatous 

Sampling 

The sites were sampled in mid-summer beginning in the summer following seeding in 2003, 

2004, and 2005. The densities of the seeded grasses and leafy spurge were counted in 0.2 by 

0.5 m frames (Daubenmire) placed at random in each treatment plot. Biomass production was 

sampled within one 1.0 by 1.0 m frame placed at random in each treatment plot. All leafy spurge 

and seeded grasses were clipped to ground level (3 cm) within the frame. The clipped material 

was oven dried to constant weight and weighed. Analysis of variance was used to determine 

significant seeding and herbicide treatment effects on the densities and biomass of seeded grass 

and leafy spurge. 

Results 

Grass density. Grass establishment as measured by density was improved by fencing to exclude 

grazing animals. While there was no statistical comparison, grass density was observed to be 

nearly ten times greater on the study inside the fence than outside the fence (see Figures 1 and 2). 

Protecting establishing grasses from grazing during the first year will improve establishment 

because it takes one year for the rooting system to develop and prevent the plants from being uprooted by grazing animals. 

Grass establishment differed depending on the species seeded regardless of grazing during 

establishment. Orchard grass, thickspike wheatgrass, and bluebunch wheatgrass established well 

at both sites (see Figures 1 and 2). Big bluegrass had better establishment on the unfenced site 

than the fenced site. This difference may be due to differences in the temperature or 

precipitation associated with the year of seeding rather than a grazing effect. Great Basin wild 

rye did not establish consistently on either site. Establishment of Great Basin wild rye may have 

been greater if it had been seeded in the spring, as opposed to fall. 

 

The densities of grasses that did establish were greater where herbicides suppressed leafy spurge 

compared to the no herbicide control at both sites. The result was the same for picloram and 

imazapic. Clearly, herbicidal suppression of leafy spurge is a requirement for consistent 

establishment of forage grasses in leafy spurge infested pastures. 

NRCS−Montana−Technical Note−Invasive Species−MT-4 3
Figure 1. The density of grasses that established on the fenced site measured from 2003 through 

2005 following various herbicide treatments. Bars with the same letters are not significantly 

different. 

Bluebunch wheatgrass

0

100

200

300

400

500

none

picloram

imazipic

Big bluegrass

Til el rs per m 2

0

100

200

300

400

500

Orchard grass

0

100

200

300

400

500

Thickspike wheatgrass

Til el rs per m 2

0

100

200

300

400

500

2003 2004 2005 2003 2004 2005

ab

a

ab

ab

a

c

c bc

ab

a a

a

a

a

b b b b

a a

ab ab

b

b

c c c

a

a a

c

b

b

c

b b

Grass biomass. Grass biomass production per square meter depended on the species seeded and 

the herbicide treatment. Where grasses established, their biomass production was increased in 

the herbicide treatments (data not shown). Combining herbicide suppression of leafy spurge and 

seeding forage grass species increased livestock forage production. 

NRCS−Montana−Technical Note−Invasive Species−MT-4 4
Figure 2. The effect of herbicide treatment and grass seed treatment on seeded grass density on the 

site that was not fenced. The grass seeding treatments are no grass seeded (none), bluebunch 

wheatgrass (PSSP) big bluegrass (POAM), Great Basin wild rye (LECI), orchard grass (DAGL), 

and thickspike wheatgrass (ELLA). Bars with the same letters are not significantly different. 

Tillers m/ 2

0

10

20

30

40

50

60

None Picloram Imazapic

Tillers/m 2

0

10

20

30

40

50

a

b

b

a

a

b bc

cd

None PSSP POAM LECI DAGL ELLA

Leafy spurge density. Picloram and imazapic reduced leafy spurge density similarly on the 

fenced site (see Figure 3). On the unfenced site, leafy spurge density was significantly lower in 

the picloram treatment than the imazapic treatment, and both herbicide treatments resulted in 

lower leafy spurge density than the control two years after application (see Figure 4). It is more 

likely that the difference between sites is the result of environmental differences between years 

of application than grazing. On the fenced site, leafy spurge density increased from 2003 to 

2004 indicating a recovery of leafy spurge two years after treatment (see Figure 3). Also on the 

fenced site, the grass seeding treatment did not affect leafy spurge density indicating that where 

grass established, an expected decrease in leafy spurge density from increased competition with 

the grasses was not detected (data not shown). 

NRCS−Montana−Technical Note−Invasive Species−MT-4 5
Figure 3. The density of leafy spurge in herbicide treatments on the fenced site from 2003 through 

2005. Bars with the same letter are not significantly different. 

Stems per m 2

0

50

100

150

200

250

None

Picloram

Imazapic

2003 2004 2005

a

e

e

b

d

cd

bc

d d

Figure 4. The density of leafy spurge in the herbicide treatments on the fenced site in 2004 and 

2005. Letters above bars indicate differences among herbicide treatments and years. 

Stems/m 2

0

20

40

60

80

100

120

None

Picloram

Imazipic

2004 2005

ab

c

a a

c

b

Leafy spurge biomass. On the fenced site, herbicide treatment reduced leafy spurge biomass but 

the reduction depended on the grass seeding treatment (see Figure 5). Neither picloram nor 

imazapic reduced leafy spurge biomass production per square meter compared to the no 

herbicide control where no grass was seeded, or where big bluegrass, Great Basin wild rye, or 

thickspike wheatgrass was seeded. Big bluegrass and Great Basin wild rye had poor 

establishment on this site. It was expected that thickspike wheatgrass would reduce leafy spurge 

production where herbicides were applied because this grass established well in those plots and 

NRCS−Montana−Technical Note−Invasive Species−MT-4 6
because it has a rhizomatous root system which one would expect to compete more directly with 

leafy spurge than bunchgrasses. Perhaps over time the root system of thickspike wheatgrass will 

increase and this grass may become more competitive with leafy spurge. 

Where bluebunch wheatgrass was seeded, imazapic reduced leafy spurge production compared 

to the control, and picloram resulted in the lowest leafy spurge production (see Figure 5). Where 

orchard grass was seeded, picloram, but not imazapic, reduced leafy spurge production compared 

to the no herbicide control (see Figure 5). The reduction in leafy spurge biomass in these grass 

treatments suggests a competitive effect of the grasses on leafy spurge. The difference in the 

herbicide treatments within grass seeding treatments suggests an herbicide effect on the 

competitiveness of the grass with leafy spurge either through subtle differences in the density 

reduction of spurge or herbicide injury to the grass. 

The results of herbicide and seeding treatments on leafy spurge biomass on the site that was not 

fenced was highly variable most likely because the grass establishment was not consistent (data 

not shown). 

Figure 5. Leafy spurge biomass in grass seeding and herbicide treatment plots on the unfenced site. 

The grass seeding treatments are no grass seeded (none), bluebunch wheatgrass (PSSP) big 

bluegrass (POAM), Great Basin wild rye (LECI), orchard grass (DAGL), and thickspike 

wheatgrass (ELLA). Bars with the same letters are not significantly different. 

Leafy spurge biomass (g/m 2

)

0

20

40

60

80

None

Picloram

Imazipic

bc

abab

a

d

cd

ab

abc

bc

ab

ab

abc

ab

d

bcd bc

abc

cd

None PSSP POAM LECI DAGL ELLA

Management Implications 

The results of this study demonstrate the difficulties of managing leafy spurge and the 

importance of integrated management of this weed. Herbicidal suppression of leafy spurge can 

be variable as was seen in the difference between sites in this study. On the fenced site, both 

herbicides reduced leafy spurge by about 80 percent, whereas on the unfenced site only picloram 

reduced leafy spurge, and the reduction was only about 66 percent (see Figures 3 and 4). In 

addition, results indicate herbicidal suppression will only be short term. On the fenced site 

NRCS−Montana−Technical Note−Invasive Species−MT-4 7
where herbicidal suppression of leafy spurge was 80 percent one year after application, 

suppression was only about 50 percent in the second and third years after treatment (see 

Figure 3). Using herbicides to improve the establishment of competitive grasses will increase 

the suppression of leafy spurge. Where bluebunch wheatgrass and orchard grass established 

using picloram, leafy spurge production was reduced compared to most of the other treatments 

(see Figure 5). Using herbicides to establish perennial grasses in leafy spurge infestations will 

also increase forage production for livestock. Where herbicides were applied, seeded grass 

biomass production was greater than where no herbicides were applied on this degraded site. 

Leafy spurge was observed to regenerate where herbicides were applied and where grasses 

established (see Figure 6). This suggests that sustainable management of leafy spurge in many 

situations will require more than herbicidal and competitive suppression. Aphthona flea beetles 

have been released on this site. Aphthona larvae feed in the leafy spurge roots and rhizomes and 

have reduced densities of leafy spurge on many infested sites. In addition to Aphthona, goat 

grazing is being used to target leafy spurge. Long-term data from this demonstration will be 

used to document the integration of herbicidal, re-vegetation, biological, and grazing control of 

leafy spurge. 

Figure 6. Leafy spurge regeneration in a plot treated with picloram and seeded with bluebunch 

wheatgrass. Sustainable suppression of leafy spurge will require biological control insects or sheep 

or goat grazing to suppress the regenerating spurge. 

NRCS−Montana−Technical Note−Invasive Species−MT-4 8
References

Ferrell, M.A., T.D. Whitson, D.W. Koch, and A.E. Gade. 1998. Leafy spurge control with 

several grass species. Weed Technol. 12:374-380. 

Lajeunesse, S., R. Sheley, C. Duncan, and R. Lym. 1999. Leafy Spurge. In: Biology and 

Management of Noxious Rangeland Weeds. Oregon State Press. Pages 249-260. 

Lym, R.G. 1998. The biology and integrated management of leafy spurge (Euphorbia esula) on 

North Dakota rangeland. Weed Technol. 12:367-373. 

Masters, R.A., D.D. Beran, and R.E. Gaussoin. 2001. Restoring tallgrass prairie species 

mixtures on leafy spurge-infested rangeland. J. Range Manage. 54: 362-369. 

NRCS−Montana−Technical Note−Invasive Species−MT-4 9