Written by Chris Boerboom, UW Extension Weed Scientist (edited for FdL area by Mike Rankin)

 
       Dandelion has been and probably always will continue to be a problem perennial weed in field crops.  It seems to possess all of the critical characteristics needed for survival in Wisconsin.   It’s a hardy perennial, produces seeds by the millions, lets Mother Nature wind blow the seeds to every corner of every field, and has seeds that will germinate and flourish at any time during the growing season.  All of these characteristics make for big trouble in no-till and alfalfa fields.   

        Controlling dandelions with spring burndown applications of 2,4-D and/or glyphosate are not always effective.  However, fall herbicide treatments work exceptionally well and need to be considered as a mainstay approach to keeping dandelions from populating faster than a small town in China.  University of Wisconsin weed scientists have routinely evaluated different fall strategies for controlling dandelions.  The trial results in Table 1 was established after corn stalks were chopped off in the fall of 2006.  The herbicide treatments were applied on November 14.  The weather during that week (3 days before and after the 14th) was relatively cold with an average of 38⁰ F as the daily high temperature and 27⁰ F for the daily low temperature. The dandelions ranged in size, but were not extremely large and appeared to have some frost damage from earlier in the month. 

        Despite the weather conditions that did not seem to be highly favorable for herbicide activity, several treatments provided excellent dandelion control into the spring.  The first seven herbicide treatments in the table were applied as single herbicide products to provide a basis for understanding their relative contribution to the subsequent tank mixtures.  All of the sulfonylurea herbicides provided excellent initial control of dandelions in April, but some of the dandelions started to recover by mid-May and control dropped below 90%.  Roundup Original Max and 1 qt/a 2,4-D were not as effective as the sulfonylureas, which may be related to their generally less consistent control of dandelion and the cold temperatures when they were applied. 

        Almost all of the herbicide tank mixtures provided excellent control in April and three of the treatments controlled the dandelions almost completely through mid-May.  While many of the single herbicide products were not able to control dandelions into May, combinations of some herbicides increased the control noticeably.  For instance, Synchrony + Express + 2,4-D controlled dandelions better than any of the single herbicides.  This trial supports previous UW research in showing that there are several effective fall herbicide treatments that can be used to control dandelions.  This trial also re- affirms that the sulfonylurea herbicides can be applied late into the fall under cold weather conditions and maintain effective dandelion control.  This trial certainly suggests that fall herbicide treatments may be a worthy option to consider for dandelion control. 

        Remember that certain herbicides limit the crop that can be planted the following spring.  Basis and Princep can only be followed by corn in the spring and Synchrony can only be followed by soybeans.  Autumn, Express, glyphosate, and 2,4-D can be followed by either crop.   Some herbicides provided residual activity into the spring, which reduced the need for a spring burndown herbicide application at this site.  The residual activity may have been more apparent in this trial because of the late fall application date.  Treatments containing Synchrony and Autumn had notable annual grass and broadleaf residual activity.

Abbreviations: COC = crop oil concentrate,
    NIS = nonionic surfactant, AMS = ammonium sulfate.