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Conditions are Right for Fall Dandelion Control in Corn and Soybean

By Jeffrey L. Gunsolus, Extension agronomist-weed science

An early corn and soybean harvest and good weather conditions are keeping the window of opportunity open for fall dandelion control this year. Fall is an excellent time to target several herbaceous perennials including: alfalfa, Canada thistle and dandelion. A fall application is more effective than a spring application because systemic herbicides such as glyphosate, 2,4-D, Express, Basis and Synchrony tend to accumulate in greater amounts in a perennial plant's roots or rhizomes after a fall application. Movement to the below ground roots and rhizome buds increases herbicide effectiveness and possibly decreases winter hardiness of the plant.

Ideal conditions for fall application would include application after a light frost but before a hard frost that damages leaf tissue. Healthy leaf tissue that is not heavily covered in crop residue and daytime air temperatures at or above 50 degrees Fahrenheit will increase herbicide uptake and improve weed control. Weed scientists at the University of Wisconsin Extension have done extensive research on fall dandelion control.

Depending upon the level of dandelion infestation, other weed species present and amount of money that you wish to spend, various options exist. In general, a fall application of 2 pts./A of 2,4-D ester will provide effective fall control. If other weeds are present, a tank mixture of 2,4-D ester with glyphosate would be appropriate. Past research at Wisconsin indicates the addition of sulfonylurea herbicides (e.g. Express) increases the effectiveness of dandelion control later into the growing season as application temperatures decrease. Addition of the sulfonylurea herbicides Synchrony and Basis can also provide residual weed control activity into the spring but crop rotation sequence is critical. When used in the fall, rotations are limited to soybean and corn when using Synchrony and Basis, respectively.

For more discussion of fall herbicide applications to terminate alfalfa see the September 30, 2010 MN Crop News titled "Plan Now for Successful Corn after Alfalfa" by Jeff Coulter.
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