By: James Jackson, Extension Program Specialist; Robert Lyons, Professor and Extension Range Specialist; The Texas A&M University System
Yucca infests about 19 million acres of Texas rangeland, mostly in the western two-thirds of the state. Some of the 30-plus yucca species in Texas are beneficial to livestock and wildlife. For example, deer and livestock relish the flowers and fruit of Spanish dagger yucca.
However, many species cause problems when they develop dense stands—they use the water and nutrients needed by more-desirable plants. Examples of the problem species are San Angelo yucca and twisted leaf yucca.
Yucca plants have one or more whorls of leaves growing from a common root crown. The leaves are long, straight, fibrous, sharply pointed, and covered with thick wax.
The methods that control yucca best (76 to 100 percent mortality) are individual plant treatments. However; some herbicides applied broadcast can reach 56 to 75 percent control (see Extension publication Chemical Weed and Brush Control Suggestions for Rangeland, http://www.agrilifebookstore.org/SearchResults.asp?Search=1466&- Submit=Search).
Two Brush Busters methods to control yucca are effective, easy to use, and environmentally responsible: One uses a low-volume herbicide plus oil; the other uses undiluted herbicide. Both methods have three steps and treat each whorl. They can enable you to remove the yucca without damaging desirable plants.
Controlling yucca is not a one-time job. Because livestock and wildlife spread the seeds, new plants will emerge continually. Check your pastures periodically and control the unwanted plants.
Professionals with the Texas A&M AgriLife Extension Service have developed and approved these Brush Busters methods for yucca control. Although weather and other conditions may cause your results to vary, these methods should kill 7 of 10 yucca plants.
Brush Busters Herbicide + Oil Whorl Spray
Works best: When you want to control yucca and honey mesquite at the same time and with the same treatment. The mesquite stem diameter must be less than 1.5 inches.
When to Apply: Spring and summer during the growing season
1. Prepare the equipment
The herbicide mix can be applied with a backpack sprayer, a pump-up garden sprayer, or a sprayer mounted on an all-terrain vehicle.
The spray gun should have a ConeJet 5500-X1 adjustable cone nozzle. This nozzle will reduce herbicide usage by about 80 percent.
To reduce clogging and dripping, use a 100-meshscreen/check valve behind the nozzle.
2. Mix the herbicide with oil
Use a mixture of triclopyr ester (trade names: Remedy Ultra, Clear Pasture, and Triclopyr 4EC) and diesel fuel oil or basal oil. The oil will help the herbicide cover the plant thoroughly and enable the plant to absorb the chemical.
The recommend mixture is 15 percent triclopyr ester and 85 percent diesel fuel oil or vegetable oil (see table below).
When mixing triclopyr ester with oil, pour the required amount of triclopyr ester into the mixing container or spray tank; then add enough oil to get the total volume desired. Shake the mixture vigorously until it is mixed thoroughly.
To identify the plants already treated, add 1 ounce of Hi-Light blue spray marking dye per gallon of spray mix.
3. Spray the yucca
Make sure that the spray gun has the 5500-X1 nozzle. Position the nozzle in the center of each whorl and spray for at least 2 seconds. If applied properly, the triclopyr + oil method is the least expensive combination method for controlling yucca. The cost rises if you use basal oil instead of diesel.
Keep these points in mind
- Always follow the herbicide label directions.
- Do not spray wet yuccas.
Brush Busters Undiluted Whorl Spray
Works best: If you cannot use the Herbicide + Oil Whorl Spray method because you have only a few yucca plants but no backpack sprayer or proper nozzle
When to Apply: Spring or summer
1. Prepare the equipment
Use an application device that can measure and deliver individual 2-cc to 4-cc doses of herbicide. To treat a few yucca plants, you may use a disposable syringe.
For many plants, use an automatic syringe or exact-delivery handgun, such as a drench gun. Because these two devices connect to a reservoir (such as a drench bladder or herbicide container), you do not have to refill them manually.
Triclopyr ester, the active ingredient in the herbicides for this method, corrodes plastics. After each use, thoroughly clean the syringe or drench gun with warm, soapy water and lubricate it with mineral oil.
2. Prepare the herbicide
Use herbicides containing triclopyr ester at 4 pounds per gallon. To identify the plants already treated, add 1 ounce of Hi-Light blue spray marking dye to each gallon of herbicide.
Apply 2 to 4 cc of undiluted triclopyr to each yucca whorl. The 4-cc rate will kill more plants, but at a cost of about 8 cents per whorl for the herbicide alone. Control at the 2-cc rate may drop 10 percent or more, but the herbicide will cost about 4 cents per whorl.
3. Spray the yucca
Dose the undiluted triclopyr into the center of each whorl.
Keep these points in mind
- Follow the directions on the herbicide label.
- Do not spray wet yuccas.
- Do not use premixed or ready-to-use triclopyr herbicides for this method.
- Clean the application equipment thoroughly after each use.
Download a printer-friendly version of this publication: How to Take the Luck out of Controlling Yucca
Do you have a question -or- need to contact an expert?