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
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
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.