Leafy Spurge Control
Following Herbicide Applications
in the Tri River Area
December 2000
leafy spurge
A. Wayne Cooley (deceased)
former Area Extension Agent
Tri River Area
CSU Extension
Montrose, Colorado
Webb Callicut
Coordinator
Delta County Noxious Weed Program
Delta, Colorado
Cooperators
Steve and Rachel Allen
Delta County, Colorado
Ed Pauls
Ouray County, Colorado
American Cyanamid
Dow Elanco

TABLE OF CONTENTS

Introduction
Objectives
Materials and Methods
Results and Discussion
Summary and Conclusion
Table 1: Leafy Spurge Treatment List · Fruitland Mesa, Steve and Rachel Allen Ranch, October 10, 1996
Table 2: Leafy Spurge Treatment List · Ed Pauls Ranch, formerly Jenny Phillips Ranch at Ridgeway, Colorado
Table 3: Leafy Spurge Control on Fruitland Mesa · Steve and Rachel Allen Ranch
Table 4: Leafy Spurge Control on Miller Mesa · Ed Pauls Ranch Ranch, formerly Jenny Phillips Ranch

Introduction

Leafy spurge is native to Eurasia and was brought into the United States as a seed impurity around 1827. Leafy spurge seems to be a serious problem only in North America where it infests almost 2.5 million acres. The greatest infestation is primarily in southern Canada and the north central United States. Leafy spurge is found in several areas of Colorado and has become more wide spread in the Tri River Area in the past few years.

Leafy spurge flowers are yellowish-green, small, arranged in numerous small clusters and subtended by paired heart-shaped yellow-green bracts. Roots are brown, containing numerous pink buds, which may produce new shoots or roots.

Leafy spurge is a perennial that reproduces from seed as well as a vigorous root system that reaches depths up to 14 feet.

Seed capsules explode when dry; often projecting seeds as far as 15 feet. Seeds may be viable in the soil for at least eight years.

The entire plant contains a milky juice and it has been reported to cause severe irritation of the mouth and digestive tract in cattle if eaten. In some cases the severe irritation can result in death.

Leafy spurge is extremely competitive and generally eliminates most desirable vegetation. The extensive root system, which contains large nutrient reserves makes leafy spurge very difficult to control.

Objectives

Evaluate pasture and/or rangeland registered herbicides for activity on leafy spurge. In addition, develop a leafy spurge control program by determining the best chemical control that could be used in combination with biological control, cultural control, or mechanical control (grazing by Angora Goats).

Materials and Methods

Fruitland Mesa - Steve and Rachel Allen Ranch: A CO2 plot sprayer mounted on a Honda ATV was utilized to boom spray leafy spurge on October 10, 1996 on the Steve and Rachel Allen Ranch on Fruitland Mesa. A three nozzle boom (Tee Jet 8002 spray tips) delivered 11.9 gpa, traveling four mph, at 28 psi pressure at the CO2 tank. The plots were 10 feet wide by approximately 100 feet long. The herbicides, rates per acre applied, weather conditions at time of application and growth stage of leafy spurge are listed in Table I.

On June 6, 1997, treatments 4, 5, 6, & 7 were applied again to the same plot area utilizing the CO2 plot sprayer mounted on a Honda ATV. Treatment 8 which had been the untreated control was treated with Banvel + 2,4-D @ 1 qt + 1 qt/A. A two to three foot strip was left untreated between treatment 4 and 5 to be used as an untreated control. The stage of leafy spurge at application was full bloom to seed set. Conditions at application were as follows: air temperature - 72 F, relative humidity - 44%, wind - 0 mph, with clear skies.

On June 20, 1998, plot areas (treatments) 1, 2, & 3 were retreated with Tordon + 2,4-D + surfactant @ 1% + 1% + 1 qt/100 gal of solution, respectively, and the plants were sprayed to wet. Conditions at application were as follows: air temperature - mid 70's, wind from the south at three to four4 mph, and partly cloudy skies.

On August 20, 1998, plot areas (treatments) 4, 5, 6, 7, & 8 were treated with Plateau + Crop Oil @ 12 ounces + 32 ounces/A utilizing the Honda ATV plot sprayer at 11.6 gpa. The stage of development for the leafy spurge was some seed head development but no reddening of the plants. Conditions at application were as follows: air temperature 79 F, relative humidity - 46%, Wind - 0 to 2 mph, scattered clouds with light sprinkles prior to application.

Miller Mesa - Ed Pauls Ranch (formerly Jenny Phillips Ranch). The leafy spurge is well established and numerous acres are infested at this location.

Angora goats (approx. 100) were utilized to graze the leafy spurge during the summer of 1997. There were also areas were the Insectary at Palisade made insect releases for biological control evaluations.

angora goats feeding on leafy spurge
Angora Goats

An area was selected (approx. 0.5 acres) to initiate a herbicide test. For the most part, the Angora goats had not grazed this area during the summer of 1997. On September 12, 1997, herbicides were applied utilizing a Honda ATV plot sprayer that delivered 11.6 gpa total solution. There were seven treatments and three replications of each treatment. The plots were 10 feet by 100 feet. The spurge was past bloom with some plants showing considerable reddening. The weather was clear, wind 0 mph, soil temperature 45 F, relative humidity 66%, and the air temperature was 62 F. The plant population of the leafy spurge averaged 39 plants per square foot from seven randomly selected sites within the plot area. The treatments and rate per acre are listed in Table II.

Angora goats (approx. 200) were again utilized to graze the leafy spurge throughout the area in the summer of 1998.

On September 10, 1998 the plots were treated again with the same treatments as listed in Table II except treatment 7. 2,4-D was not added to treatment 7 for the re-treatment on September 10, 1998. The stage of leafy spurge in the herbicide treated areas at time of re-treatment were less than five inches tall with no seed production. The untreated control had grown normally and produced blooms. However by this date, the Angora goats had stripped the leafy spurge vegetation from the untreated control areas and only leafless stems remained. Conditions at time of re-treatment were air temperature 72 F, relative humidity 28%, wind 0 to 2 mph, and partly cloudy skies.

untreated control leafy spurge
Untreated Control

Results and Discussion

Fruitland Mesa - Steve & Rachel Allen Ranch: Plot areas 1, 2, and 3 treated with Tordon or Tordon + 2,4-D in the fall of 1996 exhibited 90 percent control of leafy spurge 7 months after application (Table III). However, re-growth at different levels was evident 20 months after the initial application of Tordon or Tordon + 2,4-D. Tordon at 1 and 2 qts/A resulted in 65 and 75 percent control 20 months after application. The Tordon + 2,4-D treatment resulted in only 25 percent control 20 months after application. Results from the re-treatment of these plot areas on June 20, 1998 was observed by Webb Callicutt in the summer of 1999. A visual evaluation was made by Webb and the control was greater than 80 percent.

Plot areas 4, 5, 6, & 7 which were treated with Curtail, Crossbow and two rates of Roundup + 2,4-D, respectively, did not provide acceptable control of leafy spurge seven months after the fall application or 12 months after the follow up spring (June 6, 1997) treatment (Table III). The Banvel + 2,4-D treatment applied on June 6, 1997 provided some stunting and plant population reduction 12 months after application but would not be considered acceptable control.

In fact, plots 4, 5, 6, 7, & 8, resulted in 0 percent control of leafy spurge 14 months after the last application.

Results from the re-treatment of these plots with Plateau on August 20, 1998 was observed by Webb Callicutt in the summer of 1999. A visual evaluation was made by Webb and the control was greater than 80 percent.

Miller Mesa - Ed Pauls Ranch (formerly Jenny Phillips Ranch). All rates of Plateau and the Tordon + 2,4-D treatment provided excellent control of leafy spurge nine months after application (Table IV). At 12 months after application, re-growth was observed in all plots to varying degrees. However, the re-growth had only reached two to five inches in height with no seed production in 1998. Plots were retreated with the same treatments again in the fall of 1998.

Plots were evaluated June 24, 1999 (6.5 months after second herbicide applications). Percent control of leafy spurge (Table IV) was much greater 6.5 months after the second herbicide applications for all treatments when compared to 12 months after a single herbicide application. Leafy spurge populations have not been completely eliminated, however the plants present in the Plateau treated plots were severely stunted and deformed. The Tordon treatment resulted in the best percent control, however the plants present did not exhibit the deformity and were taller than the Plateau treated plants.

Plots were evaluated for the final time on May 24, 2000 (17.5 months after the second application). Percent control of leafy spurge (Table IV) was over 80 percent for the high rate of Plateau + Crop Oil and the Tordon treatment, with the Tordon treatment resulting in slightly better control. The other treatments did not provide satisfactory control.

Even though there was no significant differences among treatments in the second and third cuttings, the trend was there for higher yields when we added potash as compared to no additional potash.

leafy spurge treated with Plateau leafy spurge treated with Tordon
Plateau
Tordon

Applications of Tordon + 2,4-D or Plateau did not result in any adverse effect on the grass species present at 9 and 12 months after the initial treatments in the fall of 1997. However grasses were stunted as compared to the untreated control in the Plateau plots following two consecutive years of herbicide applications when evaluated June 24, 1999. The major grass species present were bluegrass and western wheatgrass.

Angora goats have been a great asset the past two summers (1997 & 1998) in keeping the vegetation stripped from the leafy spurge plants outside the herbicide test area. Without leaf area to fully replenish carbohydrate root reserves of the leafy spurge, the plants will be weakened over time (estimate five to seven years) and the population will start to decline.

Summary and Conclusions

It would be safe to say that Curtail, Crossbow, Roundup + 2,4-D, and Banvel + 2,4-D are not effective treatments for leafy spurge control at the rates tested.

Tordon and Plateau show promise as an effective chemical treatment for leafy spurge but will require at least two applications. Based on the May 24, 2000 evaluation, two applications in consecutive years will not completely eliminate the population of leafy spurge. However, the high rate of Plateau + Crop Oil and Tordon reduced population over 80 percent and with follow up annual spot treatments and good management practices, the leafy spurge can be prevented from spreading and eventually eliminated.

Angora goats can be used effectively for keeping the leafy spurge vegetation stripped and reducing the number of plants that would produce seed each year. However, the number of years required for Angora goat grazing to effectively reduce leafy spurge populations, is still to be determined. Since the use of the Angora goats was permanently lost and they did not graze the area during 1999, there can not be a determination of their effectiveness at this location.

Leafy spurge control requires a long-term commitment, and persistent control measures on an annual basis to eventually eliminate the species.

Table 1: Leafy Spurge Treatment List - Fruitland Mesa · Steve and Rachel Allen Ranch, October 10, 1996

Leafy Spurge Treatment List - Fruitland Mesa
Steve & Rachel Allen Ranch
October 10, 2996
Treatments
Rate/A
1. Tordon 1 qt
2. Tordon 2 qts
3. Tordon +2, 4-D 1 qt + 1 qt
4. Curtail 4 qts
5. Crossbow 4 qts
6. Roundup + 2, 4-D 1 pt + 1pt
7. Roundup + 2, 4-D 1 qt + 1pt
8. Untreated  
The above treatments were applied on October 10, 1996. The treatments had the addition of X-77 surfactant at a rate of 1 qt. per 100 gallons of solution. The leafy spurge ranged from 3 to 16 inches tall with an average height of 9.1 inches. Populations of leafy spurge per square foot range from 24 to 36 plants with an average of 29.6. Weather conditions at start of application were: air temperature - 71°F, clear skies, R.H. 30%, and winds at 0 mph. The plot layout and application took place between 9:30am and 11:30am.

Table 2: Leafy Spurge Treatment List - Ed Pauls Ranch, formerly Jenny Phillips Ranch at Ridgway, Colorado

Leafy Spurge Treatment List - Formerly Jenny Phillips Ranch,
Currently Ed Pauls, Ridgway, Colorado
Treatments Rate/A
1. Untreated Control  
2. Plateau + Surfactant 8 oz/A + 1qt/100 gal
3. Plateau + Crop Oil 8 oz/A + 1qt/A
4. Plateau + Crop Oil + Nitrogen Fertilizer 8 oz/A + 1 qt/A + 1 qt/A
5. Plateau + Surfactant 12 oz/A + 1 wt/100 gal
6. Plateau + Crop Oil 12 oz/A + 1qt/A
7. Tordon + 2,4-D + Surfactant 1 qt/A + 1 qt/A + 1qt/100 gal

Table 3: Leafy Spurge Control on Fruitland Mesa - Steve and Rachel Allen Ranch

Leafy Spurge Control on Fruitland Mesa: Steve & Rachel Allen Ranch
 
EVALUATION
% Control Months After Last Application _3/
Plot
Area
Treatment
Rate/A
Date of
Application
7 Months
12 Months
14 Months
20 Months
1 Tordon 1 qt. 10/10/1996 90     65
1 Tordon + 2,4-D 1% + 1% 6/20/1998   80    
2 Tordon 2 qts. 10/10/1996 90     75
2 Tordon + 2,4-D 1% + 1% 6/20/1998   85    
3 Tordon + 2,4-D 1 qt. + 1qt. 10/10/1996 90     25
3 Tordon + 2,4-D 1% + 1% 6/20/1998   85    
 
% Control Months After Last Application _3/
Plot
Area
Treatment
Rate/A
Date of
Application
7 Months
12 Months
14 Months
20 Months
4 Curtail 4 qts. 10/10/1996 20 _1/      
      6/6/1997   5   0
4 Plateau + Crop Oil 12 oz. + 32 oz. 8/20/1998   80    
5 Crossbow 4 qts. 10/10/1996 0      
      6/6/1997   0   0
5 Plateau + Crop Oil 12 oz. + 32 oz. 8/20/1998   85    
6 Roundup + 2,4-D 1 pt. + 1 qt. 10/10/1996 40      
      6/6/1997   0   0
6 Plateau + Crop Oil 12 oz. + 32 oz. 8/20/1998   85    
  % Control Months After Last Application _3/
Plot
Area
Treatment
Rate/A
Date of
Application
7 Months
12 Months
14 Months
20 Months
7 Roundip + 2,4-D 1 qt. + 1 pt. 10/10/1996 60      
      6/6/1997   0   0
7 Plateau + Crop Oil 12 oz. + 32 oz. 8/20/1998   80    
8 Untreated Control 0 10/10/1996 0      
8 Banvel + 2,4-D 1 qt. + 1 qt. 6/6/1997   50 _2/    
8 Plateau + Crop Oil 12 oz. + 32 oz. 8/20/1998   85    
_1/ All Plants stunted, delayed flower formation
_2/ 90 percent of plants stunted, 50% plant reduction
_3/ % Control are visual evaluations

Table 4: Leafy Spurge Control on Miller Mesa Ed Pauls Ranch (Formerly Jenny Phillips Ranch)

Leafy Spurge Control on Miller Mesa Ed Pauls Ranch
(Formerly Jenny Phillips Ranch)
 
Evaluation
% Control Months After Last Application
Treatment
Rate/A
Date of
Application
6 1/2 Months 5_/
9 Months 2_/
12 Months 3_/
17 1/2 Months 6_/
Untreated Control 0 9/12/1997   32.5 23.3 1_/  
9/10/1998 32.2 1_/     0
Plateau + Sufactant 8 oz _ 1 qt./100 gal 9/12/1997   96.7 33.0  
9/10/1998 75.8     38.3
Plateau + Crop Oil 8 oz. + 1 qt. 9/12/1997   99.0 36.0  
9/10/1998 82.2     46.6
Plateau + Crop Oil + Nitrogen Fertilizer 8 oz. + 1 qt. + 1 qt. + 12 oz. 9/12/1997   98.8 49.8  
9/10/1998 86.2     58.3
Plateau + Sufactant 1 qt./100 gal 9/12/1997   98.8 36.0 3_/
6_/
9/10/1998 81.6     66.6
Plateau + Crop Oil 12 oz. + 1 qt. 9/12/1997   99.8 66.5  
9/10/1998 93.9     81.6
Tordon + 2,4-D + Sufactant 1 qt. + 1 qt. + 1 qt./100 gal 9/12/1997   98.3 59.6  
9/10/1998 4_/ 98.5     86.6
1_/ Average number of plants per square foot.
2_/ % Control is visual evaluations - average of 3 reps.
3_/ % Control was converted from number of plants per square foot in all treated areas as compared to population in untreated control - average of 3 reps - Herbicide treated plants were stunted, (2-5 inches tall), while untreated control developed normally.
4_/ 2,4-D was not included for this treatment.
5_/ % Control was converted from number of plants per square foot in all treated areas as compared to populations in untreated control (average of 3 reps). Herbicide treated plants were severaly stunted (0.25-1.0 inch tall) and showing deformites, while untreated control plants developed normally and were 10-15 inches tall.
6_/ % Control is visual evaluation - average of three reps by two different people.

Colorado State University, U.S. Department of Agriculture and Delta, Mesa, Montrose & Ouray Counties cooperating. Extension programs are available to all without discrimination. No endorsement of products is intended nor is criticism of products mentioned.


Page Maintained by Norraine Harvey, Administrative Technician
Colorado State University - Tri River Area
Mesa County Extension
2775 Highway 50, P.O. Box 20,000-5028
Grand Junction, CO 81502-5028