Proper Herbicide Application Timing Maximizes Invasive Plant Control

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)
Canada thistle should be fully emerged in late spring to early summer to maximize control with selective herbicides. Apply Milestone® herbicide  at 5 to 7 fluid ounces after all plants have emerged and some plants are at the bud growth stage. Read details regarding application timing of various herbicides at 

BIENNIAL THISTLES:  Bull (Cirsium vulgare), musk (Carduus nutans), plumeless (Carduus acanthoides)

Selective herbicides can be applied in spring and early summer from rosette to early flower growth stage. Milestone® herbicide can be applied at 3 to 5 fluid ounces per acre  to rosettes and early-bolting plants.  Apply the 5 fluid ounce rate from the late bolt to early flower growth stage.

SPOTTED and DIFFUSE KNAPWEED (Centaurea stoebe and C. diffusa)
Spotted knapweed can be controlled from spring through fall depending on the herbicide selected.  Milestone® herbicide at 5 to 7 fl oz/A may be applied any time 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)
The key to controlling Russian knapweed is applying a selective herbicide at the proper plant growth stage. Applications of Milestone® herbicide 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. Remember that Russian knapweed often doesn't show herbicide injury symptoms the season the treatment is applied.


LEAFY SPURGE (Euphorbia esula)
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). Herbicides alone or in combination with biological agents can contain and control infestations.  Tordon® 22K applied at 1 to 2 quarts of product per acre (qt/A) can be applied at true-flower growth stage.  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.)
Preventing establishment of invasive knotweeds is the highest management priority. Once plants are 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. Multiple applications will be necessary to provide long-term control.

TEASEL (Dipsacus sylvestris)

Teasel often grows in moist areas near wetlands or on stream banks.  Individual plants can be dug by hand, but on larger infestations, selective herbicides provide the most cost-effective solution.  Herbicides can be applied in spring or early summer to rosettes or bolting plants to stop seed production.  Follow the link below to read more about managing teasel.



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.


Updated June 2019


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