Keyes, J.D., Area Range and Animal Scientist, Utah State University
Banks. J, Extension Agent, Utah State University
Ralphs, M, Research Rangeland Management Specialist, USDA-Agricultural Research Service, Poisonous Plant Laboratory
Ransom, C, Associate Professor, Plants, Soils, and Climate Dept., Utah State University

ABSTRACT

Broom snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby) is a native invasive species that prospers on arid rangelands following disturbance.  A study was initiated to evaluate the effectiveness of potential herbicides to control broom snakeweed growing on a blue grama site in the Colorado Plateau and the sagebrush steppe in the Great Basin.  Herbicide treatments were applied in a randomized block design and  replicated in 4 blocks at both locations. The herbicides Tordon 22k Grazon P+D, Escort XP, Telar XP, Milestone, and Clarity were applied at the high and mid-point recommended rates. Spring and fall applications were made to evaluate seasonal differences.   Broom snakeweed density and associated plant cover were evaluated on each site prior to herbicide treatment in June 2008 and one year after treatment at peak standing crop (June 2009).  Tordon 22K (0.28 or 0.56 kg/ha) was most effective when applied either spring or fall. Grazon (1.42 kg/ha) and Milestone (0.12 kg/ha) were most effective when applied in fall   Perennial grass cover increased with increasing efficacy of the herbicides.  Grass cover on Tordon plots was 2.5 fold greater than the untreated check.

Reputation

Broom snakeweed has been considered a desperado of plant species for numerous decades.  The poisonous property of perennial snakeweed was documented as early as 1936.  Researchers found that ingestion could cause death in ruminants.  Sometime later, after years of incrimination by ranchers, studies verified that snakeweed can also cause abortion in ruminants. Snakeweed poisoning can be the source of retained placentas, pre-mature calves that are weak and underweight, and other reproductive disorders ( Carpenter, Ethridge, and Sosebee, 1990).

Description

Broom snakeweed (Gutierrezia sarothrae (Pursh)Britt. & Rusby) is an undesirable perennial half-shrub found on much of the rangeland in the western half of the United States and northern areas of Mexico.  Often called matchbrush, broomweed, brownweed, yellow-top, torchweed or turpentine-weed, it is a serious problem throughout the arid ranges of North America.  Ranchers and land managers have long struggled with adverse snakeweed communities.

Snakeweed has unbranched woody stems that grow upward from a basal crown giving it a broom shaped appearance. These stems die back each winter, and new growth starts from the crown in early spring. Once established, snakeweed typically survives 4 to 7 years (Dittberner, 1971). Each plant can produce 2036 to 3928 seeds/plant Seeds held in dried flower heads are gradually dispersed over winter. Seeds generally drop close to the parent plant because they have no specialized structures such as wings to aid in long range dispersal.  Seeds remain viable into spring, but rapidly disintegrate after May if they remain exposed on the soil surface (Wood, McDaniel, and Clason,1997).

Losses

The production and economic losses caused by snakeweed infestations stem from the adverse effects on two complementary processes. The forage yield is reduced on infested areas and livestock production efficiency is impaired when the plant is consumed (Carpenter et al., 1990).

Snakeweed often can become a totally dominant species following some type of disturbance to the range such as fire, overgrazing, or drought (McDaniel and Torrell, 1987).  When snakeweed is controlled, grass production increases.  Typically, grass yield increases 4 to 6 fold after a dense snakeweed stand dies-out or when the weed is removed by herbicide spraying (McDaniel, Pieper, and Donart, 1982).

Consumption can cause abortions in livestock if eaten at a certain stage of pregnancy (Dollahite and Anthony, 1957).  Abortion happens when snakeweed is grazed during the last trimester of gestation (James, Panter, and Nielsen, 1992). In general, snakeweed poisoning has a substantial economic impact on animal efficiency when cattle are grazing pastures with moderate to heavy infestations.  The revenue per cow producing unit received from snakeweed infested pastures is 22% less with a moderate infestation and 45 percent less with a heavy infestation (Carpenter, Ethridge, and Sosebee, 1991).

Indication

Improvements in herbicide efficacy and treatment recommendations have made it possible to economically control problem stands of snakeweed (Carpenter et al., 1991).  Although there has been extensive research on the control and eradication of this plant, as new products are developed investigations need to be made to keep ranchers and land managers aware of what is most effective.  New rangeland herbicides are currently available. 

The objective of this study was to compare some of the new rangeland herbicides with picloram and metsulfuron.  We wanted to look at season of application and measure the response of desirable species.  The desired result was to find an efficient and economical way of controlling snakeweed infestations for ranchers and land managers.

Our Study Areas

We chose two sites, one on the Colorado Plateau and another in the Great Basin.  The first site is located 36 km north of Monticello, UT (N 28 13’ 06.99”, W 109 25’ 05.49”).  The plant community consists of Blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths), Needle and thread (Stipa comata Trin. & Rupr), Indian ricegrass (Stipa hymenoidesR. & S.), Mormon Tea (Ephedra viridisCoville), Four wing salt bush (Atriplex canescens(Pursh) Nutt.), and Big basin sagebrush (ArtemisiatridentataNutt. ssp. tridentata).  The site has been used exclusively for grazing, and suffered extreme drought in 1996.  The density of mature snakeweed plants at the beginning of the study in 2008 was 15 plants/m².

The second site is located 12 km west of Nephi UT (N 39˚ 43’ 44.702”, W 111˚ 53’ 28.891”).  The original plant community was Wyoming big sagebrush (Artemisia tridentata var. wyomingensis (Beetle & A. Young) Welsh) and Indian ricegrass (Stipa hymenoides R. & S.).  A wildfire burned the site in July 1998 and it was seeded the following winter to crested wheatgrass (Agropyron cristatum L.).  Snakeweed reinvaded the site and its density averaged 2.1 plants·m^-2 in 2002.  A new crop of snakeweed seedlings established during the wet year of 2005, and the density of mature snakeweed plants at the beginning of the study in 2008 was 19 plants / m².

Experimental Design

The experimental design was a completely randomized block design.  There were 6 commercial herbicides used in the project.  They were Clarity, Telar, Escort, Milestone, Grazon, and Tordon. The herbicides were selected as to their potential for controlling invasive shrubs.  Each herbicide was applied at two different rates plus an untreated control segment for a total of 13 treatments (Table 1).  The treatments were applied in the spring (June) and fall (August) 2008 using a back pack sprayer.  Plot size was 3 x 10 m.  Treatments and seasons were replicated in four blocks at the two locations.         

Density of snakeweed plants was counted along 1 x 10 m belt transects running down the center of the plots.  Foliar cover was determined by the line intercept method for snakeweed, perennial grasses, annual grass, forbs and shrubs.  Density and cover measurements were taken before treatment in June 2008, and one year after treatment at peak standing crop (23 June 2009).

Table 1. Herbicide Treatment Rates

Herbicide	Trade Name	Rate	Rate
		Product/acre	ae/ai
Dicamba	Clarity	16 fl oz	.56
		32	1.12
Chlorsulfuron	Telar	0.5 oz	.046
		1.0	.092
Metsulfuron	Escort	0.5 oz	.058
		1.0	.115
Aminopyralid	Milestone	5 fl oz	.087
		7	.123
Picloram + 2,4-D	Grazon	2 pt	0.71
		4 pt	1.42
Untreated check

*percent acid equivalent/active ingredient

Snakeweed Control

Colorado Plateau

At the Colorado Plateau site, initial density of snakeweed in 2008 was 15.1 plants/m² and its foliar cover was 19%.  Total herbaceous cover was 25%.  There was an area wide die off of snakeweed in 2009.  As a short-lived perennial that propagates by seed, snakeweed needs optimal environmental conditions and will die out from drought stress or insect damage (Ralphs and Sanders, 2002).

Snakeweed density in the untreated check plot declined to 2.5% (Table 2), and all snakeweed plants in the treated plots were killed.  Perennial grass cover averaged 4% prior to treatment in 2008.  It increased to 10% in 2009 in the spring treatments, but only 8% in the fall treatments (Table 3).  Reduction in snakeweed competition for the remainder of the 2008 growing season benefitted the grasses in the spring treatments.

Great Basin

At the site in the Great Basin initial density of snakeweed in 2008 was 19 plants/m² and its cover was 16%.  Total herbaceous cover was 23%.  In 2009, density of snakeweed in the untreated check plot was 14.16 plants / m².  Averaged over rates and seasons, tordon killed more snakeweed plants that any other treatment (Table 2).  The high rate of Tordon (0.56 kg/ha) gave near total control in both seasons.  Milestone was effective when applied in the fall, and the high rate (0.12 kg/ha) gave 90% control.  Escort was more effective in the fall and its high rate (0.115 kg/ha) gave 83% control.  Telar and Clarity were ineffective.

Table 2. Snakeweed density and control one year after treatment.

Herbicide	Rate	Rate	Density		Herbicide	Control %
	Product/acre	ae/ai	Spring n/m2	Fall n/m2	Mean n/m2	Spring	Fall
Nephi
Check			13.67	14.65	14.16a
Clarity	16 fl oz	.56	17.25	16.43	13.97a	0	0
	32 fl oz	1.12	11.10	11.10		19	24
Telar	0.5 oz	.046	14.44	17.50	14.31a	0	0
	1.0	.092	11.59	13.70		15	7
Escort	0.5 oz	.058	11.02 s	5.60*	7.84bc	19	62
	1.0	.115	12.17 s	2.57*		9	83
Milestone	5 fl oz	.087	12.0 s	5.30*	6.58c	12	64
	7	.123	7.93* s	1.07*		42	93
Grazon	2 pt	0.71	12.44	17.31	8.69b	9	0
	4 pt	1.42	3.55* s	1.45*		75	90
Tordon	1 pt	.28	6.42*	4.10*	2.71d	54	72
	2 pt	.56	0.25*	0.08*		98	99
Monticello
Check			3.2	1.8	2.5
All Herbicides			0	0	0

 

Table 3.  Foliar cover of perennial grasses and snakeweed prior to treatment in 2008 and one year after treatment in 2009.

Herbicide	Rate	Rate	Perennial Grass		Herbicide	Snakeweed		Herbicide
	Product	ae/ai	Spring	Fall	Mean	Spring	Fall	Mean
Nephi
2008			6	5		18	15
2009
Check			8	8	8a	34	33	34a
Clarity	16 fl oz	.53	10	11	11b	32	22*	21b
	32	1012	13	11
Telar	0.5 oz	.046	13	11	13b	36	36	30a
	1.0	.092	13	16*		21*	25*
Escort	0.5 oz	0.58	14	12	14bc	24*	11*	15b
	1.0	.115	15*	11		25*	3*
Milestone	5 fl oz	.087	10	10	13b	11*	3*	7cd
	7	.123	15*	14		8*	0*
Grazon	2 pt	0.71	13	17*	17cd	21*	11*	9c
	4	1042	22*	17*		5*	1*
Tordon	1 pt	028	21	19*	19d	12*	3*	3d
	2	056	23*	19*		0*	0*
Monticello
2008			4	4		19	19
2009			10	8		0	0

Management Implications

In the American Southwest, Broom snakeweed is an ever-increasing problem for range managers.  As efforts are made to increase plant variety for wildlife and livestock, as well as environmental health, snakeweed invades and quickly becomes a monoculture.  

Increasing the productivity of palatable range plants is the main benefit derived from broom snakeweed control (McDaniel, 1981).  Prior studies have suggested that for enhanced re-growth of perennial grasses it is necessary to attain nearly 100% control of snakeweed plants (McDaniel, Peiper, and Donart, 1982).

Data in this study shows that Tordon at a higher rate can achieve this control target.  Both spring and fall applications were successful.  Land managers are able to apply this pesticide at their convenience.  Fall applications of Milestone, Grazon, and Escort also showed possibilities of reaching the target control. 

Forage production increased several fold when snakeweed competition was eliminated.    Reduction in snakeweed competition for the remainder of the 2008 growing season benefitted the grasses in the spring treatments.  In fac the Monticello site had become barren of Broom snakeweed, and the grass species flourished.

References

Carpenter, B.D., Ethridge, D.E., and Sosebee, R.E.  1990. Economic Losses from Broom Snakeweed Poisoning in Cattle.  Rangelands.  Vol. 12, No. 4.  pp. 206-208.

Dittberner, D.L. 1971. A demographic study of some semidesert grassland plants.  Masters thesis, Las Cruces New Mexico: New Mexico State Univ. 81 p.

Wood, B. L., K. C. McDaniel, and D. Clason.  1997. Broom snakeweed (Gutierrezia sarothrae) dispersal, viability, and germination.  Weed Sci. 45:77-84.

Carpenter, B.D., Ethridge, D.E., and Sosebee, R.E.  1990. Economic Losses from Broom Snakeweed Poisoning in Cattle.  Rangelands.  Vol. 12, No. 4.  pp. 206-208.

McDaniel, K.C. and L.A. Torell. 1987.  Ecology and management of broom snakeweed.  pp. 101-115 in: J.L. Capinera (ed.), Integrated Pest Management on Rangeland, A Shortgrass Prairie Perspective. Westview Press, Boulder CO.

McDaniel, K. C., R. D. Pieper, and G. B. Donart. 1982. Grass response following thinning of broom snakeweed. J. Range Manage. 35:142.45.

Dollahite, J.W. and W.V. Anthony 1957.  Poisoning of cattle with Gutierrezia microcephala, a perennial broomweed. J. Am. Vet. Med. Assoc. 130:525-530.

James, L.F., Panter, K.E., Nielsen, D.B. & Molyneaux, R.J.  1992.  The effect of natural toxins on reproduction in livestock.  Journal of Animal Science.  70:1573-1579.

Carpenter, B.D., Ethridge, D.E., and Sosebee, R.E.  1991.  Economics of Broom snakeweed control on the southern plains.  Journal of Range Management.  Vol. 44, No. 3, p 232-237.

Ralphs, M.H. and Sanders, K.D.  2002.  Population cycles of broom snakeweed in the Colorado Plateau and Snake River Plains.  Journal of Range Management.  Vol. 55,  No. 4, pp. 406-411.

McDaniel, K.C. 1981.  Ecology, toxicity and control of broom snakeweed.  Proceedings of the Trans-Pecos Poison Plant Symposium, Fort Stockton, TX.

McDaniel, K.C., R.D. Pieper and G.B. Donart. 1982.  Grass response following thinning of broom snakeweed.  Journal of Range Management. 35:219-222.

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