Onion weed control

Weeds are ahead of the onions this year. Kill weeds soon or your will miss the opportunity.

Many onions were planted later than normal this year due to the wet field conditions, so they are behind in their development. Unfortunately, the weeds have not waited for the onions to catch up. Ladysthumb smartweed is growing especially well and needs to be controlled soon or it will have to be removed by hand. After the 3-4 leaf stage, it becomes very tolerant of GoalTender and other postemergence herbicides.

If onions are in the early 2 leaf stage, GoalTender may be applied up to 4 oz. product per acre (0.125 lb. ai). At the onion 3 leaf stage, Chateau may be applied at 2 oz. product per acre (0.064 lb. ai). Both of these treatments may be combined with Prowl H2O at 2 qt. per acre for additional residual control of all annual weeds. Both of these treatments will be partially effective against ladysthumb and other broadleaves, but may not kill all of the weeds. Cultivation and hand weeding may be needed to remove remaining weeds. If the ladysthumb is not killed to the ground, it will resprout from the roots or the bare red stems.

The presence of any weeds in onions will reduce yields and delay maturity. Therefore, try to control them as early as possible. Continue to apply residual herbicides through the middle of July. With the choice of Chateau, Dual Magnum, Outlook and Prowl H2O, growers have many potential combinations for long term weed control of most annual weeds.

Dr. Zandstra’s work is funded in part by MSU’s AgBioResearch.

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