Postemergence weed control in onion

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.

The erratic spring weather has resulted in poor to fair preemergence weed control in many onion fields, as well as several other crops. Late planted onions are just reaching the mature one leaf stage and weeds are germinating and growing rapidly. Goal is labeled for application at the onion 2 leaf stage. It can cause onion injury if applied earlier. This leaves growers in a quandary about what to do.

Grasses can be controlled with applications of Fusilade, Poast or SelectMax plus a surfactant. In addition, all interplanted barley should have been killed by now. The new formulation of oxyfluorfen, GoalTender 4SC, is safer on onions and will cause less potential injury than Goal 2XL if applied to onions just entering the 2 leaf stage. One fluid oz of GoalTender contains the same amount of active ingredient as 2 oz of Goal 2XL.

The Nortron 4 SC label has been approved for onions. Nortron controls many broadleaves and is very safe on onions. Growers may try some Nortron in fields in which the weeds have gotten large before the onion 2 leaf stage.

Dual Magnum or Outlook should have been applied for nutsedge suppression by now. If one of these herbicides has been applied already, the other can be applied later to maintain suppression well into July. Remember that Prowl, Dual Magnum and Outlook all need at least 0.25 inch rain or irrigation to move them into the plant to be effective.

Chateau at the 3 to 6 leaf stage will improve both postemergence control and subsequent preemergence suppression of many broadleaves. It should be applied between applications of Prowl, Dual Magnum or Outlook. In tank mixes with GoalTender and Prowl H2O, it did not cause crop injury, but tank mixes with other formulations did cause crop injury.

Onion weed suppression during the next 4 weeks is critical to a good onion crop. Growers should use all measures within their means to keep the fields free of weeds. Onions will suffer yield loss from early season weed competition.

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