University of Illinois

No. 4/April 17, 1998

Knockdown of Existing Vegetation in No-Tillage Systems

The unusually mild winter has allowed many annual weeds to flourish in untilled areas. Given the delays in early preplant herbicide applications due to wet fields, much of the existing vegetation has attained considerable size. In most situations, producers should plan to control existing vegetation prior to planting no-till corn or soybeans.

Several soil-applied herbicides used in corn and soybeans have both soil and foliar activity. This foliar activity can provide some control of small annual weeds. In corn, products such as atrazine or cyanazine or premixes containing these herbicides can provide control of small weeds. In soybeans, metribuzin (Sencor or Lexone, in Canopy and Turbo), Authority Broadleaf/Canopy XL, and Pursuit all have foliar activity and can be applied prior to planting.

Keep in mind that these herbicides can afford some control of small annual weeds, especially when applied with a crop-oil concentrate or liquid nitrogen solution. If existing vegetation is larger than 2 to 3 inches, plan to add another herbicide to improve the knockdown activity. 2,4-D LV ester at one pint per acre can be added to most corn or soybean preplant herbicides if applications are made at least one week before planting. Banvel or Marksman may be applied with other preplant corn herbicides, while Assure II or Matador, Fusion, Poast Plus or Prestige, and Select may be tank-mixed with preplant soybean herbicides to improve annual grass control.

Gramoxone Extra, Roundup Ultra, or Touchdown 5 have foliar activity, but all lack any soil-residual activity. These herbicides are often tank-mixed with corn or soybean preplant herbicides to improve control of existing vegetation.

Marshal McGlamery (mmcglame@ and Aaron Hager (, Department of Crop Sciences, (217)333-4424