Turf Tips
10/18/2010

How late is too late to control broadleaf weeds?

Due to the current drought conditions for many in Indiana we have recommended holding off on herbicide applications until rain returns to drought stressed turf. Herbicides are most effective on weeds that are not drought-stressed and herbicides can be damaging when applied to drought-stressed turf. As we continue to wait for significant rains to return to these drought stressed areas the question many are asking is how late in the year can I apply a broadleaf herbicide to control dandelions, white clover, ground ivy and other broadleaf weeds. Generally, the best answer is that broadleaf herbicides can be applied in Indiana until mid-November and still provide effective control. This timing is +/- 2 weeks depending upon your location in the state. Broadleaf week control in Northern Indiana is best by November 1, whereas broadleaf weeks can effectively be controlled in southern Indiana prior to December 1.

Many herbicides are effective in late fall because plants are more likely to translocate (move downward) herbicides into root and stem tissues as the day lengths shorten and the temperatures cool. Typically, this will occur near or following our first frosts which has recently occurred. Previous research shows that 2,4-D and/or dicamba were far more effective in controlling dandelions and Canada thistle when applied 1 to 10 days after the first fall frost than when applied 5 to 11 days before the frost (Wilson and Michiels, 2003). Other work at Michigan State found that "good dandelion control can result from herbicides applied through late October, even when the plants are not actively growing." (Hanson and Branham, 1988). More recently, research at Purdue by Reicher and Weisenberger (2007) found the following in regards to ground ivy control and application timing (also see Figure 1):

In all cases read the herbicide label before making an application. Read the herbicide label carefully if the area you want to treat has recently been seeded. Most herbicides require that newly seeded turf be germinated and mown 1-2 times prior to a herbicide application.

 


Fig. 1. Percent ground ivy cover in June as affected by fall herbicide application timing. Means followed by the same letter are not significantly different at P ≤ 0.05. From Reicher and Weisenberger, 2007.

Sources:

Hanson, K. V., and Branham, B. E. 1988. Broadleaf weed control research update: II. Late fall weed control. Proc. of the 58th Annu. Mich. Turfgrass Conf. 17:44-51.

Reicher, Z. J., and Weisenberger, D. V. 2007. Herbicide selection and application timing in the fall affects control of ground ivy. Online. Applied Turfgrass Science doi:10.1094/ATS-2007-0831-01-RS.

Wilson, R. G., and Michiels, A. 2003. Fall herbicide treatmets affect carbohydrate content in roots of Canada thistle (Cirsium arvense) and dandelion (Taraxacum officinale). Weed Sci. 51:299-304.

 

Aaron Patton, Turfgrass Extension Specialist

 


Send corrections, suggestions, and comments to biehlj@purdue.edu