Common chickweed control in onions

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 growing slowly, but many are now in the 2-3 leaf stage. Weeds are growing very well. Common chickweed is a greater problem than usual because of the cool season. Normally, chickweed begins to disappear by early June, and is gone by mid-month. Goal does not control chickweed, and it can form dense mats and last most of the season if not controlled. Fortunately, we now have two herbicides (Nortron and Starane Ultra) registered for postemergence use in onions that control chickweed.

Apply Nortron at one pint per acre, either alone or in combination with GoalTender. Nortron may be applied four times per season with a maximum of 4 pt/acre/year. In addition to chickweed, Norton suppresses yellow nutsedge, nightshades, pigweeds, and mustards.

Starane Ultra 2.8 L is a new formulation of Starane (fluroxypyr). The old formulation was a 1.5 lb gallon, so you use less of the new formulation to obtain the same amount of active ingredient. Apply 0.35 pt (0.123 lb ai) per acre to control several broadleaves; it may be applied twice per season between the onion 2-6 leaf stage. Starane Ultra controls chickweed, ragweed, horseweed, nightshades, common lambsquarters, and mustards. It also may be used to kill volunteer potatoes in onions. Starane Ultra causes onions to turn yellow, curl, and lay over but the symptoms are short lived and there normally is no adverse effect on onion yields. Competition from weeds normally is a much greater risk for crop yields.

In addition to GoalTender, Nortron, and Starane Ultra, Chateau has good postemergence activity on many broadleaf weeds. It normally is applied to extend preemergence control of most broadleaves, including nightshades, smartweeds, and lambsquarters which may be missed by Prowl H2O and GoalTender. If applied at the 2 oz rate, Chateau will give about six weeks preemergence control of most broadleaves. Chateau should be applied alone to avoid toxicity to onions from petroleum solvent carriers in many other pesticides.

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