Weed control in onions can be difficult. Effective preemergence herbicides do not provide acceptable annual broadleaf control. Postemergence herbicides cannot be applied until the crop has 2 or 3 true leaves plus the flag leaf.
Apply Dacthal at 4 to 7 quarts per acre or Prefar 4EC at 1.5 gallons per acre preemergence to control annual grasses and certain broadleaf weeds. Irrigate if rainfall does not occur after application.
Dual Magnum has a Special Local Needs 24 C label for use on dry bulb and green bunching onions in New Jersey. Use Dual at the rate of 0.66 to1.33 pints per acre, depending on soil type. Apply to weed free soil when direct seeded onions have fully developed the flag leaf and two true leaves. Dual Magnum controls annual grasses, nightshade species, and galinsoga. Yellow nutsedge will be suppressed or controlled at the rates on the Dual Magnum label for onions. To obtain a label, an indemnification agreement must be filled out on line agreeing not to hold the manufacturer responsible for crop damage. Obtain a copy of the label and complete the indemnification agreement on the Syngenta website, “farmassist.com”. Register or sign in, and go to “products” on the tool bar, click on “indemnified labels”, and follow the instructions. You must have a copy of the valid label to use Dual Magnum on dry bulb or green bunching onions!
Goal or Goaltender can be applied after the onions have 3 true leaves to control annual broadleaf weed seedlings. Weeds that have grown past the 4 true leaf stage of growth are likely to escape. Injury to the onion foliage should be anticipated, and more severe when applications are made during periods of cool humid cloudy weather. Repeat applications can improve weed control.
Buctril can be applied after the onions have 3 true leaves to control annual broadleaf weed seedlings. Weeds that have grown past the 4 true leaf stage of growth are likely to escape. Some injury to onion foliage should be expected. Apply Buctril in 50 to 70 gallons of spray solution per acre. Concentrated sprays can kill onions. Crop injury is more severe when applications are made during periods of cool humid cloudy weather.
Consult the Commercial Production Recommendations for rates and additional information.