Guide B-821
Revised by Leslie Beck
College of Agricultural, Consumer and Environmental Sciences, New Mexico State University
Author: Extension Weed Specialist/Associate Professor, Department of Extension Plant Sciences, New Mexico State University. (Print friendly PDF)
Figure 1. African rue flowers and green seed pods (that contain the highest levels of toxicity for foraging livestock).
African rue (Peganum harmala) is native to North Africa and to the Mediterranean region. It was introduced into the U.S. around the 1920s and was first noticed in the Deming area; however, it is now common throughout southern New Mexico and has begun moving north. The plant favors disturbed and barren areas such as oil pads, roadsides, parking lots, corrals, stockyards, and abandoned crop fields. Although African rue has traditionally been prominent in rangeland and pastures, it has started to establish within city properties and in some residential settings. This has prompted many initiatives through city representatives and government programs, such as the Bureau of Land Management and Soil and Water Conservation districts within the area, to develop management programs to help regulate the populations as they continue to spread. This has proven difficult since the plants are very drought tolerant, and produce a deep and robust perennial root system, which is the primary obstacle to effective control.
African rue is a small bright green succulent perennial herb with a bushy growth habit that reaches about 1-3 ft. in height at maturity. The plant dies back to its roots in winter and initiates new growth in late March in southern New Mexico. After spring growth, the plant often becomes senescent as soils dry in early summer, but then will undergo a second growth phase later in the season as rains are received which increases the difficulty in effective control. Leaves are alternate, smooth, and divided deeply into narrow lobes. Single flowers are born along the stem and in the leaf forks. Flowers have five white petals and produce a cylindrical 2-4 celled fruit with many seeds.
African rue is known to contain four poisonous alkaloids and is toxic to cattle, sheep, and horses. The effects on livestock include loss of appetite, trembling and loss of coordination. Severe poisoning can result in hemorrhaging in the heart and liver. Because of its bad taste and smell the plant is usually avoided by livestock, unless other forages are unavailable. The seeds are the most toxic part of the plant, with leaves somewhat less toxic (Figure 1).
Why Herbicide Application
Because of African rue’s extensive root system, efforts to eliminate the plant by traditional means such as physical removal, mowing, raking, and burning are very difficult. The plant quickly grows back after mowing or burning, and deep cultivation only divides and further spreads the roots which may develop into new plants and increasing the population. As a result, herbicides are often required for effective control; however, this still proves to be a difficult task due to the extensive root system. Numerous herbicides have been investigated for African rue control in field tests conducted by New Mexico State University, but only chemicals that are moved deep into the plant’s root system have shown to be effective. Foliar active herbicides must be applied when the plant is actively growing to maximize chemical uptake and movement (translocation) through all portions of the plant.
Soil active herbicides are applied to the surface and must be incorporated into the top 1-2 in. of the soil to activate; this is typically accomplished through irrigation or timing applications to rain events, which are often minimal and infrequent in southern New Mexico. Herbicide control by either foliar or soil active methods is usually slow, requiring a year or more to kill a plant whether it is individually or broadcast sprayed.
General Considerations
Weather conditions at the time of spraying are extremely important to successful herbicide activity. Coverage is best with low wind speeds, higher relative humidity, and cool temperatures. High air temperatures increase the spray solution volatility, and thus reduce herbicide availability to be absorbed by the plant. Optimum wind velocity is 3 to 8 mph and air temperature should be above 50° F but not exceed 85° F. Do not spray a foliar active herbicide if a rainstorm is expected within six hours of application to allow the application to dry on the plant foliage as required by the label directions.
The plant condition and growth stage at the time of application are critical for control success. Spraying African rue in the early vegetative and bloom stage in spring (April) is optimal. Active growth at the time of application is the key to maximizing the herbicide movement into and throughout the plant to cause as much injury as possible. Do not spray African rue that has been stressed from drought, disease, insects, or other causes that might have resulted in plant damage.
Herbicides recommended for African rue control often damage other nearby desirable plants as well, in particular native grasses. Thus, spraying should not be conducted in areas where grass preservation or revegetation into the area is desired. Individual plant spraying (spot-spraying) will minimize grass damage relative to broadcast spraying, but still expect some damage.
Specific Guidelines
Broadcast Foliar Spray Treatment
The proper time to foliar spray African rue varies from year to year because of specific weather conditions. Expect average to above average winter moisture to produce a prolific burst of vegetative growth of African rue in spring, which is desirable before spraying. In drought-heavy years, African rue will have poor vegetative and flower growth, and spraying is not recommended. At the time of spraying the soil temperature at a 6-inch depth should be between 70° F and 50° F. In most years, the application season and this soil temperature range occur roughly from April 1 to May 15, plus or minus 15 days.
Mixes with imazapyr alone or in combination with other herbicides have consistently provided the best African rue control in New Mexico. Imazapyr is very active on the root system and is the most common active ingredient used for commercial African rue control. Imazapyr is usually applied at a 0.75 lb active ingredient (a.i.) per acre rate, which is equivalent to 3 pints of product per acre. A surfactant should be added to the herbicide mixture at rates specified on the herbicide label. Imazapyr is a nonselective herbicide so, anticipate damage to nearby desirable plants.
Metsulfuron is another herbicide that provides fair to good African rue control when applied at a rate of 2.0 oz a.i. per acre or higher. Metsulfuron is formulated as a 60 percent active dry flowable material that when dissolved and mixed in water, is sprayed as a liquid. Metsulfuron is very active on broadleaved weeds but typically results in less harm to native grasses compared areas sprayed with imazapyr.
| Table 1. Recommended Spray Mixtures for Broadcast Application on African Rue | |||
| Trade name | Herbicide chemical name | Rate of product/acre | Rate of active ingredient (a.i.)/acre |
| Arsenal™ Habitat™ | Imazapyr | 3 pints | 0.75 lb |
|
Escort™ |
Metsulfuron | 3.2–6.4 oz | 2–4 oz |
| Spike 20P™* | Tebuthiuron | 10–15 lb of pellets | 2–3 lb |
| Row 1-2 provides best control under most New Mexico conditions. *Apply only on sandy soils. |
|||
Broadcast Soil Spray Treatment
African rue growing on rangeland with sandy soils and mixed brush may be controlled with tebuthiuron. Unlike the liquid foliar active herbicides, tebuthiuron is a dry pellet formulation that dissolves and moves into the soil with rainfall and is absorbed by the roots. Tebuthiuron provides fair to good African rue control. However, a relatively high rate of application is required, and the herbicide will likely damage nearby vegetation. This herbicide can be applied at any time of the year but prior to anticipated rainfall is optimal. The principal use of this herbicide when applied at lower rates is for control of woody shrubs, such as creosotebush, oaks and sagebrush.
Individual Plant Treatment (IPT)
For practical reasons IPT is used in areas where African rue is growing sparsely and is easier to treat individually. IPT is an effective way to control the plant, but the method is time consuming and costly if the African rue population is dense. Adding blue dye to the spray mixture helps to identify plants that have already been treated to avoid over-application, and as a check to make sure no plants in the area are skipped.
Figure 2. African rue plants growing along a roadside in Luna County, NM.
Figure 3. African rue plants that have been individually sprayed (spot-sprayed) with herbicide and blue dye mixture.
Figure 4. New vegetation growth from the previous season’s root system (notice the foliar growth that has died back to the root system from the previous season and is still present).
Hexazinone is a liquid that is applied to the soil surface next to individually 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. 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, which is the desired rate of application. Check the handle pressure and practice with water in the sprayer to calibrate this delivery rate.
Imazapyr diluted as a 3 percent mixture with water is another effective IPT. A backpack sprayer with its nozzle adjusted to wet the foliage provides satisfactory control.
| Table 2. Recommended Spray Mixtures for Individual Plant Application on African Rue | |||
| Trade name | Herbicide chemical name | Rate of product/acre | Rate of Active Ingredient (a.i.)/acre |
| Velpar | Hexazinone | 4 ml squirted on the soil surface next to each treated plant | Mix 50:50 with water in a backpack sprayer |
| Arsenal™ Habitat™ | Imazapyr | 1–3% mixed in water | Spray foliage to wet |
| Row 1 provides best control under most New Mexico conditions. | |||
For more on this topic, see the following publications:
B-806: Brush and Weed Control on New Mexico Ranges
https://pubs.nmsu.edu/_b/b-806/
CR-636: An Annotated Checklist of Poisonous and Injurious Range Plants of New Mexico
https://pubs.nmsu.edu/_circulars/CR-636/
All Livestock and Range Publications:
https://pubs.nmsu.edu/_b/
Brand names appearing in publications are for product identification purposes only. No endorsement is intended, nor is criticism implied of similar products not mentioned. Persons using such products assume responsibility for their use in accordance with current label directions of the manufacturer.
Product recommendations in this publication are provided only as a guide. The authors and New Mexico State University assume no liability resulting from their use.
Original authors: Kirk McDaniel, Extension Brush and Weed Control Specialist and Keith Duncan, Extension Brush and Weed Control Specialist.
Leslie Beck is the Extension Weed Specialist at New Mexico State University. Her research program focuses on integrated weed management systems in landscape, horticultural, and agronomic crops. Her Extension work provides the citizens of New Mexico with accurate, applicable, and effective weed identification and management strategies in multiple cropping systems.
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Revised December 2025
