Canada Thistle Control
Following Applications of Curtail
and Redeem R&P Herbicides
December 2000

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

Robbie Baird-LeValley
Area Extension Agent
Tri River Area
CSU Extension
Delta, Colorado


TABLE OF CONTENTS

Introduction
Objective
Materials and Methods
Results and Discussion
Diagram: Canada Thistle Control Following Applications of Curtail and Redeem R&P

Introduction

Canada thistle (Cirsium arvense (L.) Scop.) is an aggressive creeping perennial, that once established, becomes very competitive in irrigated pastures and mountain meadows. Canada thistle is also on the state of Colorado and Tri River Area counties noxious weed list.

Canada thistle is a native of southeastern Eurasia and was introduced into Canada as a contaminant of crop seed as early as the late 18th century. From Canada, the plant has spread throughout the United States, probably by several avenues.

Canada thistle differs from other species of the true thistles in that there are male and female flower heads, and these are on separate plants. By asexual reproduction, it is possible that a colony of male plants would produce no fruit, but still maintain itself. This weed is difficult to control and breaking up the roots by plowing or utilizing a tandem disk only serves to increase the number of plants. Root sections as short as 3 to 4 inches in length can initiate buds and a new plant can emerge and become established.

Objective

The objective of this study was to compare initial and long term control of Canada thistle when applying Curtail and Redeem R&P herbicides in a side by side comparison. Curtail has shown to be effective for control of Canada thistle 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 Canada thistle control at a lower rate per acre than Curtail.

Canada Thistle Untreated Control

Materials and Methods

Broadcast applications were made 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.

Two tests were initiated on the LeValley Ranch near Crawford, Colorado on May 22, 2000. Curtail was applied at 2 qts/A and the Redeem R&P was applied at 3 pts/A. Both herbicides had the addition of X-77 surfactant at a rate of 1 qt/100 gallons of spray solution. The environmental conditions at the beginning of the applications at 9:00 a.m. were air temperature 61 F, soil temperature 50 F, relative humidity 44 percent, wind 0 mph, and clear skies. Applications were completed for both locations by 10:45 a.m. The thistle was actively growing and was 12 to 14 inches tall at both locations. The plot length at location 1 was 400 feet and location 2 was 270 feet (see plot diagram).

Curtail
Redeem R&P

Results and Discussion

Location 1 was evaluated on June 23, 2000 for vegetative control and pictures were taken of both treatments and the untreated control (UTC). Curtail and Redeem R&P both resulted in 100 percent control of the vegetative portion of the Canada thistle. Location 1 and 2 will be evaluated in 2001 to determine the effectiveness of root kill of the Canada thistle.

Diagram: Canada Thistle Control Following Applications of Curtail and Redeem R&P

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