Onion weed control

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Onions have been developing slowly due to the cool weather, and most are in the flag to 2 leaf stage. Weeds are also germinating and need to be controlled. The small size of onions makes postemergence applications somewhat problematic.

Barley should have been sprayed by now with one of the graminicides to kill it. If allowed to grow much longer, the barley will compete with the onions and use up moisture and nutrients. Most onions are well-established and no longer need the protection provided by the cover crops.

If onions are in the 2 leaf stage, it is safe to apply several herbicides in a tank mix. Prowl H2O plus GoalTender and a grass killer is a good combination for onions in the full 2 leaf stage. If Outlook is being applied, it should be applied alone to avoid foliar burn from the carrier. As soon as onions reach the 3 leaf stage, Chateau should be applied alone to provide extended preemergence control of most broadleaves. Chateau also has postemergence activity and is safe on most onions at 2 oz product per acre.

If volunteer potatoes are a problem, apply Starane Ultra at the onion 2-6 leaf stage. The recommended rate for Starane Ultra is 0.35 pt/acre.

It is important to kill weeds in onions as early as possible. Once the weeds are established, it is very difficult to control them, and onions are very susceptible to competition. If you have specific questions about onion weed control, please call me for advice at: 517-353-6637

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