Russian Knapweed Control
Following Applications of
Curtail and Redeem R&P Herbicides
in the Tri River Area
December 2000

A. Wayne Cooley (deceased)
former Area Extension Agent
Tri River Area
CSU Extension
Montrose, Colorado


TABLE OF CONTENTS

Introduction
Objectives
Materials and Methods
Results and Discussion
Diagram I: Summer Broadcast Application at LeValley Ranch
Diagram II: Fall Application at LeValley Ranch
Diagram III: Summer Handgun Application at Barb Young Ranch

Introduction

Russian knapweed (Centaurea repens L.) is a deep rooted creeping perennial plant that was first introduced into North America in about 1898. Russian knapweed grows in a variety of soil types and is not associated with any particular soil. Much of the initial invasion of this plant has been traced to contaminated alfalfa seed that was imported from Russia in the 1920's. More recent spread of Russian knapweed seed can be attributed to several different means including motorized vehicles, contaminated gravel for road surfacing, irrigation water, farm equipment, as well as humans, birds, and mammals.

Russian knapweed forms dense stands and tends to exclude other plants due to its competitiveness and allelopathic properties. Due to these properties of Russian knapweed, infested areas eliminate native plant species as well as desirable agricultural plant species. Russian knapweed is also on the state and local noxious weed list.

Objectives

The objective of this study was to compare the control of Russian knapweed when applying Curtail and Redeem R&P herbicides in a side by side comparison. Curtail has shown to be effective for the control of Russian knapweed in the Tri River Area. However, this is the first year to test Redeem R&P in the area. Redeem R&P does have a federal registration for Russian knapweed control at a lower use rate per acre than Curtail.

Materials and Methods

Broadcast treatments were applied using a CO2 plot sprayer with a three nozzle boom (five foot spray swath) mounted on a Honda ATV. Nozzles were on 20 inch spacings, containing Tee Jet 8002 spray tips. Applications were made at 4 mph with a pressure of 28 psi at the CO2 tank. The sprayer was calibrated and delivered 11.6 gpa of solution at the above speed, pressure, nozzle spacing, and spray tips.

The handgun applications utilized a single nozzle equipped with a OC 8 spray tip with 28 psi pressure at the CO2 tank and the plant foliage was sprayed to wet.

All treatments at each location had the addition of X-77 non-ionic surfactant at a rate of 1 qt per 100 gallons of solution.

LeValley Ranch - Summer Applications: Russian knapweed herbicide treatments were initiated on June 12, 2000 with Redeem R&P at 3 pts/A and 4 pts/A , Curtail at 3 qts/A, and an untreated control (UTC). The area treated is shown in Diagram I.

The environmental conditions at 9:00 a.m. were air temperature 68 F, wind 0 mph, and relative humidity 40 percent. The Russian knapweed was drought stressed, 7 to 24 inches tall, and in the late bud stage of development.

LeValley Ranch - Fall Applications: Russian knapweed herbicide treatments were initiated on September 5, 2000 with Curtail at 3 qts/A, Redeem R&P at 3 pts/A and 4 pts/A, and an UTC. The area treated is shown in Diagram II.

The environmental conditions at 12:15 p.m. were air temperature 75 F, wind 0 to 6 mph, soil temperature 75 F, relative humidity 48 percent, partly cloudy with intermittent showers.

The Curtail treatment was applied first which is approximately 45 feet wide (nine passes) with the last two passes (10 feet) less than the 3 qt/A rate due to being low on CO2. Light showers started at 1:00 p.m. just as the Curtail treatment was completed.

The CO2 tank was replaced before starting the Redeem R&P treatment of 3 pts/A. The Redeem R&P treatment of 3 pts/A is approximately 40 feet wide (eight passes) and this treatment was started at 1:20 p.m. After four passes, at 1:30 p.m., light showers stopped application for 5 minutes. The Redeem R&P at 3 pts/A was completed and one pass of Redeem R&P at 4 pts/A and light showers at 1:44 p.m. stopped application for 10 minutes. The remaining seven passes of Redeem R&P at 4 pts/A was completed without further rainfall by 2:00 p.m. The wind increased to over 10 mph by 2:20 p.m. as additional clouds starting moving in from the west.

The Russian knapweed had produced seed and was from 9 to 24 inches tall with an average height of 16 inches. Due to the drought conditions during the 2000 growing season approximately 25 percent of the Russian knapweed plants were totally brown at application.

Barb Young Ranch - Summer Applications: Russian knapweed herbicide treatments were initiated on June 14, 2000 with handgun applications of Redeem R&P at 1.5 oz/gal of water, 2.0 oz/gal of water, and Curtail at 2.0 oz/gal of water and the plants were sprayed to wet. The area treated is shown in Diagram III.

The environmental conditions at 8:00 a.m. were air temperature 60 F, wind 0 mph, and relative humidity 50 percent. All treatments had been completed by 10:00 a.m.

The Russian knapweed was 7 to 36 inches tall (depending on moisture availability) and was in the bud to early flower stage of development. There were other species at this location that will be evaluated, however not all species were present for all treatments. The species present were Canada thistle (bud stage), poverty sumpweed (bud stage), rabbit brush, and greasewood.

Results and Discussion

LeValley Ranch - Summer Applications: On June 23, 2000 pictures were taken of the plots and the treated Russian knapweed was observed for herbicidal activity. The Curtail treated plants were showing some chlorosis as well as the Redeem R&P treated Russian knapweed that were not as drought stressed at time of application.

Redeem R&P

The true evaluation of perennial weeds is the number of plants that emerge from the extensive root system the following year or years. All locations will be evaluated extensively during the 2001 growing season.

Diagram I: Summer Broadcast Application at LeValley Ranch

Russian Knapweed Control
Following Application of Curtail and Redeem R&P Herbicides
Summer Broadcast Application
LeValley Ranch

 

Diagram II: Fall Application at LeValley Ranch

Russian Knapweed Control Following of Curtail
and Redeem R&P Herbicides
Fall Broadcast Application - LeValley Ranch

Diagram III: Summer Handgun Application at Barb Young Ranch

Russian Knapweed Control Following Applications of
Curtail and Redeem R&P Herbicides
Summer Handgun Application
Barb Young Ranch

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