Proper Application Timing Maximizes Invasive Plant Control

Published in the spring 2015 magazine issues of TechLine Invasive Plant News, Western Range & Wildlands Edition and Prairie & Grasslands Edition. Relevant region is noted for each species.

Spring and early summer can be excellent times to control actively growing invasive plants with herbicides. Applying herbicides to the target plant at the optimum growth stage is important to maximize control. The following guidelines provide information on the best application timing and rate to control key invasive plants.

CANADA THISTLE (Cirsium arvense)
(Western Edition / Prairie Edition)

Late spring and early summer applications of Milestone® on Canada thistle should be made after all plants have emerged and basal leaves are expanded. It is better to wait until some of the plants are at the bud growth stage to be sure that all plants are emerged before applying Milestone at 5 to 7 fluid ounces per acre (fl oz/A). Use the 7 fl oz/A rate at later growth stages. 

BIENNIAL THISTLES:  Bull (Cirsium vulgare), musk (Carduus nutans), plumeless (Carduus acanthoides)
(Western Edition / Prairie Edition)

Milestone at 3 to 5 fl oz/A can be applied in spring and early summer from rosette to early flower growth stage. Use the 5 fluid ounce rate at the late bolt to early flower growth stage.

SPOTTED and DIFFUSE KNAPWEED (Centaurea stoebe and C. diffusa)
(Western Edition / Prairie Edition)

Milestone at 5 to 7 fl oz/A may be applied any time during the growing season when plants are actively growing. Applications made during the late bud to bloom stage will not stop seed production the year of treatment.

RUSSIAN KNAPWEED (Acroptilon repens)
(Western Edition)

Applications of Milestone at 5 to 7 fl oz/A should be delayed until Russian knapweed has bolted and is in the early bud to flower growth stage; applications can be made through the fall. It is important to remember that herbicide efficacy symptoms do not always show on Russian knapweed the season the treatment is made.


LEAFY SPURGE (Euphorbia esula)
(Western Edition / Prairie Edition)

The optimum time to treat leafy spurge with most herbicides is at the true flower growth stage, which is after the yellow bract is formed (late spring to early summer). Apply Tordon® 22K alone at 1 to 2 quarts of product per acre (qt/A) at true flower. When applying Tordon 22K at rates less than 1 qt/A add 2,4-D at 1 qt/A (1 lb ae/A). The addition of OverDrive herbicide at 4 oz/A may improve leafy spurge control by up to 20%.  For suppression of leafy spurge on sensitive sites apply a tank mix of 7 fl oz/A Milestone® plus 1 qt/A 2,4-D plus 4 oz/A of OverDrive.

KNOTWEEDS  (Fallopia spp.)
(Western Edition)

Preventing knotweed establishment is the highest priority for management. Once established, eradication is extremely difficult.  Optimum suppression of invasive knotweeds with Milestone herbicide at 9 to 14 fl oz/A is obtained when applications are made to plants that are at least 3 to 4 feet tall. On Bohemian knotweed, total application volume of 100 gallons per acre or greater increased control. Multiple applications will be necessary to provide long-term control.

TEASEL (Dipsacus sylvestris)

The most cost effective treatment for teasel is the use of selective foliar applied herbicides. Milestone at 4 to 7 fl oz/A provides good to excellent control of teasel and should be applied in spring or early summer to rosettes or bolting plants to stop seed production. The higher application rate of 5 or 7 fl oz/A is recommended for plants at the bolting growth stage.



Managing invasive plants such as Siberian elm (Ulmus pumila), buckthorn (Rhamnus cathartica), honeysuckle (Lonicera spp.), locust (Robinia spp.), and other woody species is often difficult. Herbicide treatments alone or in combination with fire and mechanical methods, such as cutting and shredding, can provide cost effective removal of woody vegetation. Use of herbicides minimizes site disturbance compared to mechanical methods, and can be applied on a variety of sites often throughout the year. Follow the link below for detailed information regarding foliar, basal, and cut surface herbicide applications on woody plants.



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®Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. Milestone is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Label precautions apply to forage treated with Milestone and to manure from animals that have consumed treated forage within the last three days. Consult the label for full details. Tordon 22K is a federally Restricted Use Pesticide.  Always read and follow label instructions.