ISSUE 15   September 17, 2009


Fall is the best time to control winter annual weeds such as shepherd’s-purse and horseweed (marestail), biennial weeds such as bull and musk thistle, and simple perennial weeds such as dandelion and curly dock. Control is usually maximized if effective herbicides are applied after a light frost and before the soil is frozen. As long as plants appear to be alive with green and normal textured leaves, herbicides should effectively control weeds. Dandelions are usually more effectively controlled in the fall during less than ideal spraying conditions than waiting until spring. Apply herbicides when the daytime temperatures are as warm as possible and morning lows are above 32 degrees. Winter annual, biennial, and simple perennial weeds can be more effectively controlled at lower temperatures than summer annual weeds such as lambsquarters.

Glyphosate at 0.75 to 1.125 pounds acid equivalent (lbs ae)/A plus 2,4-D ester at 1.0 pint/A plus AMS at 8 to 17 pounds/100 gallon of spray mixture should effectively control nearly all winter annual, biennial and simple perennial weeds. Glyphosate should be applied at 1.125 lbs ae/A where dandelions are large, old, and numerous. Other herbicide combinations have been used in other parts of the country, but control tends to be more inconsistent.

Jeff Stachler
Agronomist - Weed Science

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