Community Ag Alliance: Managing spring weeds |

Community Ag Alliance: Managing spring weeds

One year ago, my spring weed column discussed the legal and stewardship responsibilities for all land owners and managers to control their noxious weeds. In this column, I will present weed control techniques for two of Routt County’s noxious weeds.

One of our most troublesome noxious weeds, already greening up as the snow recedes, is Houndstongue. The burs that your dog has started bringing home contain the seeds for this Colorado List B noxious weed, which is very toxic to livestock, especially horses. The fuzzy green rosettes of this tap rooted, biennial weed are already appearing and offer a great opportunity for control. Look first for the standing dead plants, which may still hold last year’s burs (pull or cut and bag these old plants) then search the ground for new plants. Pull these young plants while the soil is still moist, dig the tougher plants, then walk in ever widening circles to look for more plants to pull, dig or bag. If your infestation is serious enough to warrant spraying, apply 1 1/2 ounces per acre of Escort or 1 quart per acre of 2,4-D (each with a non-ionic surfactant) to young, actively growing plants. Continue to monitor the infestation sites for new plants and pull, dig or spray as required.

Two bio-control insects are currently being used in Canada, but neither has been approved for importation into the United States. A native moth first observed defoliating houndstongue in the Yellowstone area is currently under evaluation in Idaho as a potential bio-control.

Another serious List B weed problem in our county is Whitetop (Hoary cress). Unlike Houndstongue, Whitetop is a strongly rhizomatous, long-lived perennial which does not respond to any form of mechanical control. Any part of a root or rhizome left in the soil after trying to pull or dig the plants will generate a new plant, and mowing only induces the plants to form a shorter and denser weed cover.

Only if you are certain that recently germinated seedlings are younger than six weeks old can any control be achieved by pulling. Remember, most of the emerging plants you will see this spring are sprouts from existing roots and rhizomes and will not pull, but simply break off if you try to pull or dig them. Herbicide spraying should be done during May when adequate leaf area is available for chemical absorption and before the bright white blossoms show any signs of fading. The recommended herbicides are Escort at 1 1/2 ounces per acre or Telar at 1 ounce per acre, either to be used with a non-ionic surfactant.

When buying or using any herbicide always read and follow the label instructions exactly. The label and MSDS (Material Safety Data Sheet) for all herbicides is available online, so you have a chance to review the use and safety aspects of any product you are considering using before you buy. Please call The Routt County Weed Program at 970-870-5246 or email with any questions about weed control.

Greg Brown is weed supervisor for the Routt County Weed Program

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