Weeds in the Conservation Reserve Program (CRP) may be worse than normal this year because of last year’s drought in some areas of the state, according to Richard Zollinger, North Dakota State University Extension Service weed specialist.

""Dry conditions last year and haying, where allowed, mean weeds may invade these areas where there was little ground cover from desirable grasses to compete with weed infestations,"" Zollinger says.

Growers are doing more to control weeds, according to recent surveys. Historically, only 2 percent to 3 percent of CRP acres were treated with herbicides to control weeds. However, in the most recent survey taken in 2004, that figure increased to more than 10 percent.

2,4-D and Tordon have been the most widely used herbicides, but use of Curtail for Canada thistle control has increased.

“Most herbicides that control broadleaf weeds in CRP also will kill or severely injury the legume component of the CRP stand,” Zollinger says. “The Natural Resources Conservation Service’s policy on noxious weed control allows spot spraying of noxious weed at the expense of preserving the legume. Controlling noxious weed is a priority over maintaining legumes in the mix. Always review your CRP weed control program with your local USDA Service Center before making any herbicide applications.”

Here are suggestions for controlling some weeds likely to be a problem in CRP:

Leafy spurge: Spot spray Tordon at 2 quarts per acre for the best control. For large areas, Tordon at 1 to 2 pints per acre plus 2,4-D at 1 quart per acre, provides the most cost-effective control. The optimum time for treatment is in the true flower stage of growth, which is generally mid-June. The true flower stage occurs approximately two weeks after the appearance of the bright yellow bracts. Plateau applied at 4 fluid ounces in the fall also gives good control. The addition of an MSO type adjuvant is required with Plateau.

Spotted knapweed: Tordon at 1 pint per acre, plus 2,4-D at 1 quart per acre, provides good control of plants and seedlings for two to three years. Treat when spotted knapweed is in the rosette or bud to bloom stage of growth. Banvel or 2,4-D provides good season-long control if applied in the rosette stage.

Absinth wormwood: Apply 2,4-D at 1 quart per acre in early June, when plants are at least 12 inches tall. Tordon at 0.5 to 1 pint per acre, plus 2,4-D at 1 quart per acre, extends control for more than a year and will kill seedlings that germinate. Curtail or Redeem, used for Canada and biennial thistle control, also gives excellent wormwood control.

Biennial thistles such as musk, plumeless or bull thistle: Apply 2,4-D at 1 to 1 1/2 quarts per acre when thistles are still in the rosette stage of growth. Treatment after the thistle has started to bolt is less effective. Cimarron or Cimarron Max recently has been labeled for use in CRP and provides excellent control of most biennial thistles.

Field bindweed, Canada thistle, and perennial sowthistle: Tordon at 1 to 2 quarts per acre provides the best long-term control, but may be cost prohibitive. Tordon at 1 to 2 pints per acre, plus 2,4-D at 1 quart per acre, is more economical, but only controls weeds for one season. Retreatment is required every year and it may take three to four years to reduce the size of established patches. Banvel at 1 to 2 quarts per acre control established plants for one year. 2,4-D is less expensive and effective than Tordon or Banvel and will suppress only top growth. NDSU research has shown good perennial sowthistle control with Cimarron or Cimarron Max. The optimum time for treatment is in June when plants are in the early bud stage, or in the fall.

Sagebrush, gumweed, goldenrod, buckbrush/western snowberry: Apply 2,4-D at 2 quarts per acre in early June, when new leaves are fully expanded. Adding Tordon to 2,4-D will extend control for more than one year, except for the buckbrush/snowberry.

For additional information, visit with your local county Extension agent and refer to the “North Dakota Weed Control Guide” (W253).

NDSU Agriculture Communication