May 18, 2007

With wet spring conditions in many parts of Nebraska, producers may be pressed to adjust their intended herbicide program. Each year questions arise on the limits of using preemergence herbicides on emerged corn. In 2006, Alex Martin assembled a table of these products, which we have updated for this year. Table 1 lists a number of commonly used premergence herbicides labeled for broadcast application after corn emergence, along with crop and weed stage or height information. This list is not comprehensive. If your herbicide choice is not listed in Table 1, check the label for use restrictions.

If the product you are using contains atrazine, adding a crop oil concentrate can enhance control. Atrazine is primarily translocated upward in the plant (xylem mobile). When a foliar application is made, atrazine behaves more like a contact herbicide.

If you planted glyphosate-resistant corn, tank mixing glyphosate with one of the preemergence herbicides will improve total weed control, especially if weeds are larger than you had anticipated. If you tank mix glyphosate with a preemergence product in this situation, adding 17 lbs/100 gallons of AMS will improve its performance. The same will apply to tank mixing Liberty on Liberty Link corn varieties, however, you will want to use 3 lb/ac AMS (1.5 lb/ac if tank mixing with Lumax or Lexar).

Remember, applying preemergence herbicides with a liquid nitrogen carrier is not advised. Unacceptable crop injury will occur.

Lowell Sandell
Extension Educator, Weed Science, Lincoln