USDA 

-

a 

United States Department of Agriculture 

Field Guide for Managing 

African Rue in the Southwest 

Forest Southwestern 

Service Region TP-R3-16-15 Revised June 2017 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cover Photos 

Top left: G.A. Cooper, USDA-PLANTS Database, Bugwood.org 

Bottom left: G.A. Cooper, USDA-PLANTS Database,Bugwood.org 

Right: Joseph M. DiTomaso, University of California-Davis, Bugwood.org 

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African rue (Peganum harmala) 

Caltrop family (Zygophyllaceae) 

African rue is listed as a noxious weed in both Arizonaand 

New Mexico. This field guide serves as the U.S. Forest 

Service’s recommendations for management of African rue in 

forests, woodlands, and rangelands associated with the 

Service’s Southwestern Region. The Southwestern Region 

covers Arizona and New Mexico, which together have 11 

national forests. The Region also administers 4 national 

grasslands that are located in northeastern New Mexico, 

western Oklahoma and the Texas panhandle. 

Description 

African rue (synonyms: wild rue, rue weed, Syrian rue, 

harmal, esfand, ozallaik, ruin weed) is a succulent perennial 

herb with a robust, deep-growing root system that is a major 

obstacle to plant control. 

Growth Characteristics 

• Perennial bushy herb that grows 1 to1.5 feet tall and 

3-4 feet in diameter. 

• Has a hardy woody taproot that reaches 25 feet or 

more downwards into the soil profile. Creeping, 

lateral roots are produced about 12-15 inches below 

the surface that can extend up to 20 feet away from 

the parent plant. 

• Bright green leaves are alternate, smooth and divided 

deeply into narrow lobes. Leaves have a very 

disagreeable odor when crushed. 

• Single flowers are borne along the stem and in the 

forks of leaves. Flowers have five white petals and 

produce a green, orange, or brown-colored 

cylindrical seed pod (2-4 celled) with 45-60 seeds. 

• Reproduces by seed, but new shoots and plants are 

also produced from adventitious buds along lateral 

roots. Seed is secured in a leathery fruit capsule; each 

plant may produce as many as 1,000 capsules. 

Ecology 

This weed is extremely toxic to cattle, sheep, horses, and 

humans as it contains at least four poisonous alkaloids. The 

seeds and fruit are the most toxic, followed by young leaves 

and mature leaves. However, animals typically avoid eating 

African rue because of its bad taste and smell. In addition, 

most parts of the plant have allelopathic chemicals that reduce 

the growth of surrounding native plants. 

Common in disturbed and barren areas such as roadsides, 

parking lots, oil pads, corrals, stockyards, open fields, 

abandoned crop fields, river banks, ditches and arid/semi-arid 

desert areas, especially in moist soils. It can grow in many soil 

types, including alkaline or highly saline soils. 

African rue occurs throughout most western States, including 

New Mexico, Arizona, Texas, California, Montana, Nevada, 

Oregon, and Washington. In New Mexico, it is primarily 

found in southern counties with isolated populations in central 

and northwestern counties. It is common in eastern Arizona 

and western Texas. 

Seeds and root fragments are readily transported by running 

water. Seeds can be carried in mud that sticks to vehicles, 

railcars, and earth-moving equipment; thus, new plants easily 

spread along transportation corridors. Seed may also adhere to 

the feet, fur, or feathers of animals. Seed longevity is 

unknown but is probably persistent. 

African rue undergoes robust and rapid vegetative growth 

when soil moisture is available. It favors disturbed areas such 

as those impacted by earth-moving equipment, excessive 

grazing, or vehicle use. Disturbed areas with moist soil such 

as roadsides, river or stream banks, riparian corridors, 

waterways, and drainage or irrigation ditches are especially 

susceptible. 

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This invasive weed is extremely drought tolerant and has 

“drought evader” growth characteristics. In southern New 

Mexico, plants die back to their roots during winter and initiate 

new annual growth in mid-to-late March. After spring growth 

and flowering, plants may become senescent (decrepitlooking) and die back to the woody base as soils dry during 

summer. With cooler temperatures and additional moisture 

coming later in the season, African rue usually undergoes a 

second vegetative growth phase that lasts until freeze occurs in 

early November. 

Management 

Once established,African rue is difficult to eradicate without 

impacting associated desirable plants. However, methods to 

control the plant other than by herbicidal application are quite 

limited. Grazing is not an option due to toxicity, and there are 

no known classic biocontrol agents at this time. The plant 

grows back quickly after mowing or burning, and deep 

cultivation only fragments and spreads the roots. Since African 

rue is able to regenerate from root fragments, grubbing or 

cultivation may actually increase the population size. 

The following actions should be considered when planning a 

management approach for African rue: 

• Maintain healthy plant communities to prevent or limit 

infestations of African rue. 

• Detect and eradicate new populations of African rue as 

early as possible, especially along roadways, 

waterways, and ditches. 

• Use foliar or soil-active herbicides at recommended 

rates for effective control of African rue populations. 

Table 1 summarizes some management options for common 

situations involving African rue. Further details on these 

management options are explained below. Choice of control 

method(s) for African rue depends on the land use and current 

site conditions (accessibility, terrain, soil and air temperature, 

weather, extent and density of infestations, other flora and 

fauna present, etc.). Other considerations include treatment 

effectiveness, cost, and the time needed to achieve control. 

Physical Control 

Because African rue has a complex root system consisting of 

lateral roots and a deep tap root, it is extremely difficult to 

control the plant solely through the use of mechanical methods. 

The more practical and economical way to obtain effective 

long-term control is to use herbicide treatments alone or in 

combination with a physical method. 

Manual Methods 

Hand-pulling, digging, or hoeing for control of mature plants is 

virtually impossible due to the depth of the root system. Hand 

removal of seedlings and young plants that is continued year 

after year may eventually control individual plants, but this 

approach is tedious and usually impractical. 

Mechanical Methods 

Controlling African rue by plowing or grubbing individual 

plants is ineffective since the roots are too deep to dig out and 

any root parts left in the ground will likely re-sprout. In many 

instances, cultivation may actually lead to an increase in 

population size. In certain agronomic situations, repeated deep 

cultivation combined with reseeding perennial plants has been 

found to be somewhat successful; but this is an expensive 

option. Mowing or blading also causes the plant to re-sprout 

and spread. 

Prescribed Fire 

Fire is not an effective control method as plants grow back 

rapidly after burning. 

Cultural Control 

Early detection and plant removal, especially for seedlings and 

young plants, are critical for preventing African rue 

establishment and spread. Land managers, road crews, and the 

local public should be educated on identification so they can 

report suspected populations. Vehicles, humans, and livestock 

should be discouraged from traveling through infested areas; a 

program to check and remove seeds from vehicles and 

livestock after going through infested areas should be 

implemented to help stop the spread. Hay, straw mulch, 

planting seeds, fill, and other related materials should be 

certified to be weed free before use in areas undergoing 

treatment. 

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Table 1. Management options* 

Site Physical Control Cultural Control Biological Control Chemical Control 

Roadsides Few options available. 

Combine suppression 

methods (e.g., repeat 

deep cultivation or 

mowing) with reseeding 

desired native perennial 

plants. 

Use seed, mulch, and fill 

materials certified to be 

weed-free. 

Limit disturbances along 

roadsides. 

Implement requirements for 

vehicle operations and for 

reporting infestations along 

roads. 

None known at this time. Use truck or tractor spraying 

equipment. Wash underneath to 

prevent spread. 

Ditches and Few options available. Limit disturbances along Same as above. Use herbicide with approved 

waterways Hand extraction or 

hoeing can be used to 

waterways and ditches. 

Increase public awareness 

aquatic labeling when near or in 

water. 

target seedlings. and reporting of plant 

presence along ditches and 

roadways. 

Rangeland Few options available. Use seed and forage hay 

certified to be weed-free; use 

pellets for horses in 

backcountry areas. 

When moving livestock or 

vehicles through infested 

areas, inspect mud on 

animals, clothing, and 

vehicles and remove any 

seeds before entering uninfested areas. 

Same as above. Use ground broadcast spraying 

with ATV or tractor; however, 

backpack spraying may be more 

practical in areas with difficult 

access. 

Consider individual plant treatment 

in areas with less dense infestation 

or near desirable vegetation. 

Wilderness Few options available. Use seed and forage hay Same as above. Use backpack sprayers for 

and other 

natural areas Hand removal repeated 

year after year may be 

required for effective 

control. 

certified to be weed-free; use 

pellets for horses in 

backcountry areas. 

Post signs warning visitors 

to remove seeds. 

individual plant treatment or 

ground broadcast spraying with an 

ATV or tractor, if allowed. 

* Choice of a particular management option must be in compliance with existing regulations for the land resource. 

Biological Control 

Grazing 

Grazing is not a viable option for removing African rue. Due 

to its bad taste and smell, livestock usually avoid the plant 

unless other forages are unavailable. Occasionally, African 

rue is found as a contaminant in hay bales. Effects of 

poisoning on livestock include loss of appetite, trembling, 

and loss of coordination. Severe poisoning can result in 

hemorrhaging in the heart and liver. 

Classical Biological Control 

There are no known classical biocontrol agents (insects, 

pathogens, etc.) available for African rue at this time. 

Chemical Control 

Numerous herbicides have been investigated in field trials for 

African rue control. These tests show that only chemicals 

translocated deep into the plant’s root system can effectively 

kill the weed (see table 2). Certain selective, systemic 

herbicides (e.g., metsulfuron) will suppress seasonal top 

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growth; however, most plants recover and regrow within a 

year of treatment. Unfortunately, the few herbicides that 

provide effective long-term control (e.g., imazapyr, 

tebuthiuron, and hexazinone) are nonselective and may 

cause unacceptable injury to desirable species, especially 

grasses. 

It is very important to read the herbicide label carefully and 

follow all instructions when mixing and applying any 

herbicide. Equipment used to spray herbicide should be 

calibrated. Aquatically approved formulations should be 

used in or near water. When using aquatic herbicide 

formulations, an aquatically approved surfactant should 

also be added to the spray mix. 

Considerations for Herbicide Use 

Based on research and practical experience, the following 

guidelines should be used for herbicidal control of African 

rue: 

• Plant condition and growth stage at the time of 

application are critical for control success. When 

using a foliar spray, treating African rue that is 

healthy and robust in late summer (SeptemberOctober) is optimal. Plants in the early vegetative 

and bloom stage in spring (April) can also be 

successfully controlled provided soil moisture is 

adequate. Do not spray African rue that has been 

stressed from drought, disease, insects, or other 

causes that might have resulted in dieback, 

yellowing, or other plant damage. 

• Weather conditions at the time of spraying are 

important for successful herbicide activity. Coverage 

is best with low wind speeds (3 to 8 mph) and cool 

temperatures (between 50 °F and 85 °F). Air 

temperatures above 85 °F increase spray solution 

volatility and thus reduce the amount of herbicide 

available to be absorbed by the plant. Do not spray a 

foliar-active herbicide if a rainstorm is expected 

within 6 hours of application. 

• The plant community associated with the African 

rue population should be closely evaluated before 

treating an area. Use of a nonselective herbicide 

should not be made in areas where grass 

preservation is desired. Individual plant spraying 

will minimize grass damage relative to broadcast 

spraying, but some damage should still be expected. 

• Time needed to gain control is slow, requiring a 

year or more to kill a plant when either sprayed 

foliarly or treated with a soil-active herbicide. 

Herbicide Application Options 

Broadcast foliar spray treatment – The ideal time to 

spray African rue foliarly varies from year to year because 

of specific weather conditions. Expect average to aboveaverage winter moisture to produce a prolific burst of new 

vegetation growth in spring, which is needed before 

spraying to maximize chemical uptake and movement 

(translocation) through all portions of the plant. In 

droughty years, African rue will have poor foliage and 

flower growth; therefore, spraying is not recommended. 

Similarly, healthy foliage that results from above-average 

summer rainfall can be sprayed late in the season. At the 

time of spraying, soil temperature at a 6-inch depth should 

be between 55 °F and 70 °F. In years with average to 

above-average winter precipitation, the desired growth 

stage and soil temperature range occurs roughly from April 

1 to May 15, plus or minus 15 days. In late season, the 

desired growth stage is usually from September 1 to 

October 1. 

Using imazapyr alone or in combination with other 

herbicides has consistently provided the best African rue 

control. Imazapyr (e.g., Arsenal®) is the most common 

commercial product used for African rue control. Imazapyr 

is labeled for pasture/rangeland, noncropland sites, rightsof-way, industrial areas, fence rows, non-irrigation ditch 

banks, establishment and maintenance of wildlife openings, 

and for bare ground weed control. When broadcast spraying 

larger infestations, use a 1.75 lbs. a.i. per acre rate, which is 

equivalent to 3 pints of product per acre. When spot 

treating smaller populations or isolated plants, use an IPT 

approach as described below. A surfactant should be added 

to the herbicide mixture at rates specified on the herbicide 

label. Imazapyr is a nonselective herbicide so damage to 

grasses and other associated plants should be anticipated. 

A new herbicide product called Viewpoint® (active 

ingredients: aminocyclopyrachlor + imazapyr + 

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Table 2. Herbicide recommendations 

Common 

Chemical Name 

(active 

ingredient) 

Product 

Example(s)1 

Broadcast 

Treatment 

(rate per 

acre) 

Spot 

Treatment 

(spray 

solution and 

pellets)2 

Time of Application Remarks 

Imazapyr Arsenal 

Habitat 

[others 

available] 

3 pints per acre 3% Spray healthy 

regrowth foliage in 

good condition in late 

summer or early fall. 

Imazapyr is a nonselective 

herbicide; anticipate damage 

to non-target plants from 

overspray, runoff, 

movement in soil, or root 

exudates. 

When performing IPT 

with a backpack sprayer, 

adjust nozzle to wet 

foliage thoroughly. 

Aminocyclopyrachlor 

+ metsulfuron + 

imazapyr 

Viewpoint 3–18 ounces 

per acre 

NA Same as above. This herbicide combination 

provides nonselective 

control and should only be 

used in non-crop areas. 

Metsulfuron Escort 

Ally 

3.2–6.4 ounces 

per acre 

NA Same as above. Metsulfuron is selective and 

provides seasonal foliage 

suppression but low 

mortality in African rue. 

Tebuthiuron Spike 20P 10–15 pounds 

of pellets 

NA Anytime but optimal 

time is just before a 

rain event. 

Apply only on sandy or 

coarse soils; will likely 

damage associated 

vegetation. 

Hexazinone Velpar NA Mix 50:50 with 

water in a 

backpack 

sprayer. Apply 4 

ml per plant 

(equivalent to 2 

ml undiluted 

Velpar). 

Anytime. To apply as an IPT, squirt 

4 ml of mixture on the soil 

surface next to each plant. 

Not recommended as a 

broadcast because it is 

nonselective and will 

damage or kill associated 

vegetation. 

1 Trade names for products are provided for example purposes only, and other products with the same active ingredient(s) may be available. 

Individual product labels should be examined for specific information and appropriate use with Africanrue. 

2 Spray solution is the herbicide/water ratio in a spray mix that may be used for spot treatment with backpack or hand-held sprayers. The 

amount of product applied during an annual growing season must not exceed the maximum application rate per acre as specified by the 

product label – refer to the product label for the site type and application. 

metsulfuron) provides good to excellent control of African 

rue when applied at a rate of 13 to 18 ounces of product per 

acre. Viewpoint is formulated as a dispersible granule that is 

mixed in water and applied as a liquid spray. This herbicide 

is labeled specifically for non-crop situations only, such as 

spraying rights-of-way, oil pads, parking lots, etc. It 

provides broad-spectrum control of brush and weeds 

species. Care should be exercised when using this product in 

the vicinity of crops or other desirable plants because this 

herbicide combination may injure or kill them. Read the 

herbicide label carefully for use directions. 

Broadcast soil-active treatment – African rue growing on 

rangeland with sandy to loamy soils may be controlled with 

a broadcast rate of tebuthiuron (e.g., Spike 20P®) applied at 

2 to 3 lbs. a.i. per acre. Unlike the liquid foliar-active 

herbicides, tebuthiuron is a dry pellet formulation that is 

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applied to the soil surface. These pellets remain intact until 

they are dissolved by rainfall and the chemical is moved into 

the soil where it is taken up by roots. Tebuthiuron is applied 

by aerial or ground methods and provides fair to good 

African rue control. However, damage to associated 

vegetation should always be anticipated at the relatively 

high rate of application required. 

Individual plant treatment (IPT) – IPT is an effective way 

to control the plant; however, the method is often timeconsuming and costly, especially if the African rue is dense. 

For practical reasons, IPT is ordinarily used only for small 

areas where African rue is growing sparsely and the 

infestation is easy to treat. Two active ingredients, hexazinone 

and imazapyr, are preferred IPT choices, but they are 

applied in different ways as described below: 

• Hexazinone (e.g., Velpar®) can be applied as a liquid 

directly to the soil surface next to the canopy of 

individually treated plants. For IPT, hexazinone should 

be diluted as a 50:50 mix with water in a backpack 

sprayer. A quick squirt of the handle with the nozzle 

turned to a straight stream generally administers about 

4 ml of solution (or 2 ml of active product), which is 

the desired rate of application. Before spraying, check 

the handle pressure and practice with water in the 

sprayer to calibrate this delivery rate. Adding ablue 

dye to the spray mixture helps to identify treated 

plants. Hexazinone moves into the soil profile with 

rain and is taken up by roots. Thus, application prior to 

anticipated rainfall is preferred, but the product usually 

works at any time of year. 

• Imazapyr diluted as a 3 percent mixture with water is 

effective for IPT. Most herbicide activity is through the 

foliage so use a backpack sprayer with its nozzle 

adjusted to wet the top growth of individual plants 

completely. Add blue dye to the spray mixture to help 

view spray coverage and to identify treated plants. 

Management Strategies 

Early detection and control of new African rue populations – 

especially near waterways and ditches – are important 

activities for slowing the spread of this noxious weed. In 

most cases, effective control of African rue will require 

herbicide spraying. Since each treatment situation is unique, 

site-specific management should be used. Depending on the 

intended land use and available budget, consider reseeding 

desired plant communities, as healthy plant populations can 

help deter spread of African rue. 

Even with herbicide use, it may take years to reduce the 

presence of this plant, which can regenerate from deepgrowing root parts as well as seed. Since it is ordinarily 

useless to treat an area only one time without retreatment, 

sufficient resources must be allocated for the area where 

control is attempted. After initial treatment, it is especially 

important that resources are also available to respray or 

retreat the treated area as necessary. Always anticipate the 

need for monitoring and additional control measures such as 

spot spraying with a backpack or hand-held sprayer. 

References and Further 

Information 

Abbot, L.B, D. Lepak, and D.L. Daniel. 2007. Vegetative 

and Reproductive Phenology of African rue in the 

Northern Chihuahuan Desert. The Southwestern 

Naturalist 52(2):209–218. 

Duncan, K., K. McDaniel, and M. Renz. 2005. Chemical 

Weed and Brush Control for New Mexico 

Rangelands. Las Cruces: New Mexico State Univ. 

College of Agriculture and Home Economics and 

Cooperative Extension Service. Pp. 6. Available at 

http://aces.nmsu.edu/pubs/_circulars/CR_597.pdf. 

Fact Sheet: Stop the Spread of African Rue. November 

2009. Published by the Government of South 

Australia/South Australian Arid Lands Natural 

Resources. Available at http://www.saalnrm. 

sa.gov.au/ (accessed Sept. 2014) 

Hart, C.R. 2002. African rue - Biology andManagement. 

University of Texas A&M Publication L-5429 10-02. 

Available at http://pecosbasin.tamu.edu/ 

media/2652/L-5429.pdf (accessed Sept, 2014) 

La Plata County Weed Office, 2500 Main Avenue, Durango, 

CO. Available at www.lpcweeds.org/ Africanrue.htm 

(accessed Sept. 2014) 

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McDaniel, K.C. and K. Duncan. 2006. African Rue Control: 

Ground Applications. New Mexico Cooperative 

Extension Service Publication BC-6. New Mexico 

State Univ., Las Cruces, NM. 

Michelmore, M. 1997. African rue Management— 

Distribution, Biology, Impact and Control Strategies 

for Peganum harmala L. (Zygophyllaceae) in South 

Australia. Primary Industries, SA, Port Augusta, South 

Australia. 

Northam, E. and W. Meyer et al. 2009. Non-Native Invasive 

Plants of Arizona. Produced by Conservation Districts 

and RC&D Areas of Arizona and the University of 

Arizona Cooperative Extension. Peer reviewed 

publication AZ 1482. Available at 

http://cals.arizona.edu/pubs/natresources/az1482.pdf 

(accessed Sept. 2014) 

Renz, M. and F. Sholedice. 2006. Troublesome Weeds of New 

Mexico. Las Cruces: New Mexico State University 

College of Agriculture and Home Economics and 

Cooperative Extension Service. Pp. 54-55. Available at 

http://www.emnrd.state.nm.us/fd/Publications/ 

documents/NMTroublesomeWeeds.pdf (accessed Sept. 

2014) 

The Plant Database. 2010. U.S. Department of Agriculture 

NRCS National Plant Database. Baton Rouge, LA. 

Available at http://plants.usda.gov/java/ 

profile?symbol=PEHA (accessed Sept. 2014)) 

Suggested Web Sites 

Dirty Dozen Invaders of the Southwest. 2002. 

NMSU, UA, USU, and U.S. Dept. of 

Agriculture cooperating. Available at 

http://www.invasiveweeds.com/dirty/ 

african_rue/ 

For information on invasive species: 

Plant Health and Pest Prevention Services: 

http://www.cdfa.ca.gov/phpps/ipc/weedinfo/ 

peganum.htm 

National Invasive Species Information Center: 

http://www.invasivespeciesinfo.gov/ 

Invasive and Exotic Species of North America 

https://www.invasive.org/ 

For information about calibrating spray equipment: 

NMSU Cooperative Extension Service Guide A-613, 

Sprayer Calibration. Available at 

http://aces.nmsu.edu/ pubs/_a/A-613.pdf 

Oregon Department of Agriculture, Plant Division Noxious 

Weed Control. Available at http://www.oregon.gov/ 

ODA/PLANT/WEEDS/profile_africanrue.shtml 

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For more information or 

other field guides, contact: 

USDA Forest Service 

Southwestern Region 

Forest Health 

333 Broadway Blvd., SE 

Albuquerque, NM 87102 

Or visit the Southwestern Region’s 

website for invasive species: 

http://www.fs.usda.gov/goto/r3/invasivespecies 

The use of trade or firm names in this publication is for reader 

information only and does not imply endorsement of any 

product or service by the U.S. Department of Agriculture. 

Recommendations made here for 

pesticide use are not obligatory, 

nor do they imply that discussed 

uses have been registered. All 

uses of pesticides must be 

registered by appropriate State 

and/or Federal agencies before 

they can be applied. 

CAUTION: Pesticides can be 

injurious to humans, domestic 

animals, desirable plants, and fish or other wildlife—if they 

are not handled or applied properly. Use all pesticides 

carefully and lawfully. Follow recommended practices for the 

disposal of surplus pesticides and pesticide containers.