Traditional Methods for Controlling Dyer's Woad
is relatively easy to control both with herbicides and by good farming practices. The big challenge with this particular weed is the amount of acreage infested here in Northern Utah. The analogy that fighting weeds is like fighting wildfire really holds true with Dyer's Woad. Our practice is to respond to flare-ups away from the main body of weeds, but not to spend our time or resources attacking a thousand acre piece of Woad on the hillside where the ground is not in use anyway. There are many ways to be much more cost effective on other threatening weeds that not only pose more negative impact to the public, but occupy far less ground to where the expense of applying herbicides can be justified with noticeable result. Once again, it is extremely important that you READ AND FOLLOW THE LABEL with any herbicide you chose to use.
All is not lost, however, as a very effective biological control agent
is working on the many infestations of Dyer's Woad wherever they are found. The "time line" featured near the bottom of the page represents a generalized guide to the most effective timing of chemical weed control for Dyer's Woad here in Northern Utah.
Telar® is the herbicide of choice in Weber County on Dyer's Woad for non crop sites. The one pound bottle of dispersible granules seems pricey at $300.00, but we put it out at 1/2 to 1 ounce per acre with very good results. We generally tank mix Telar® with a pint of amine just to help it along. The residual effect the year following application of Telar® is quite noticeable. Do not use this particular herbicide where planting will occur within 1 year.
For bare ground work involving Dyer's Woad, we like Arsenal® or Oust® tank mixed with diuron for most all jobs. We use Arsenal® at one quart per acre or Oust® at 3 oz per acre along with 2 quarts of diuron 4L for that same acre. The pint of amine is also a good thing with this tank mix. For us, it is very cost effective. Your results may vary. See labels for rates on your soils. CAUTION watch sloping ground for potential runoff in the event of heavy rain or overhead irrigation!
Roundup® can be used on Dyer's Woad rosettes or early growth stage if damage to grasses around the Woad is of no concern. Mowing can help if done early enough in the year. Dyer's Woad thrives here in late April or early May. This weed will continue to try and make flower heads on much shorter stems even after mowing and a follow-up cutting may not cut off all the potential seed heads. Clean off that implement before using it in another field!
Rights of Way
Along roadsides, we seldom target Dyer's Woad specifically. Campaign® is effective on early up shoots of Woad in the normal "window of opportunity" for most effective chemical mowing. We will also inject a pint of ester in with the Campaign® to aid knock down of Woad if it is well along. Telar® with a pint of amine or ester is used on roadsides where more mature Woad is prevalent. 2-4,D & Banvel® (in weed districts of course) are not very effective on larger stalks of Dyer's Woad so we do try to target this weed very early.
Dyer's Woad next to irrigation ditches and streams must be treated with care. There are some amine formulations of 2-4,D that are labeled for aquatic use where grasses under or near the noxious weeds are not desired to be killed. If grasses are of no consequence, we like Rodeo® and the appropriate surfactant. Telar® may be tempting here but the label cautions that it should not be used on irrigation ditches or canals including their outer banks.
Most labels for herbicides used in crops do not specifically mention Dyer's Woad. If rowcrops or alfalfa are being considered for a piece that has been infested with these broadleaf weeds, might be a good idea to plant cereal grains the first year, make the young grain weed free with your favorite chemical, and follow up after harvest when thistle rosettes again appear with Roundup® or 2-4,D. Then the following year, the tillage and/or chemical treatments you would normally use on rowcrops or alfalfa should keep any remaining invaders in check. Swathing alfalfa early enough to stop seed production in Dyer's Woad can be tight as this weed is one of the earliest ones to mature.
Most appropriate months for treatment of Dyer's Woad