How Late is Too Late to Control Broadleaf Weeds?

How Late is Too Late to Control Broadleaf Weeds?

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. This window can be extended if temperatures are above average and days are sunny.
 
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 in Nebraska 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 research in Michigan 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 (Reicher and Weisenberger, 2007) found the following in regards to ground ivy control and application timing (also see Figure below):

• November applications of most herbicides resulted in ground ivy control similar to earlier (September and October) applications when rated the following June.
  
• Triclopyr was the most effective and consistent in controlling ground ivy.
  
• Long-term control of ground ivy from triclopyr was not affected significantly by application date.
  
• When using three-way herbicides (2,4-D + MCPP + diacmba) or products containing fluroxypyr, applications on 1 September through 1 November were most effective.
  
• Adding carfentrazone (FMC’s Quicksilver, PBI Gordons’ Powerzone and Speedzone) to 2,4-D+MCPP+dicamba dramatically improved short-term control of ground ivy from November applications, but had little long-term benefit on any application date. Products containing carfentrazone will aid in quick “burndown” and immediate customer satisfaction when making fall applications but they may not increase long-term control, especially with ground ivy.
  

The bottom line is that if the herbicide is rated to provide excellent control on the weed that you are trying to control, it may not bee too late to control broadleaf weeds this fall. 

Other notes:

• In all cases read the herbicide label before making an application. 
• Winter annuals. Many winter annuals like henbit, common chickweed, purple deadnettle and others have already germinated and are small and easily controlled in the fall. Applications in October and November will control these small winter annual broadleaves as well as the perennial broadleaves.
• Newly seeded areas. 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. 

For more information on weed control, search this blog and archived turf tip postings and check out our Turfgrass Weed Control for Professionals Publication.

Sources:

1. 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.

2. 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.

3. 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

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What To Do With All Those Falling Leaves?

What To Do With All Those Falling Leaves?

It is that time of year when leaves are falling faster than you can rake them in many places. It is important to rake leaves when there are many leaves on the ground (so many that you can't see the turf underneath) so that heavy layers of leaves will not shade out, smother, and kill turf. However, when only a moderate number of leaves are on the ground, you can use your mower to mulch them back into the turf. Research results at Purdue and other universities demonstrates that:

• Tree leaves (both oak and maple) can be mulched without any detrimental effects on the soil or turf and usually results in improvements in soil structure.
  
• Mulching leaves into the turf will not increase thatch or disease.
  
• Leaves have no effect on soil pH and no measurable effect on nutrient availability.
  
• Mulching leaves will not result in increased weed pressure and some recent research in Michigan even suggests that mulching leaves back into your lawn can reduce dandelion populations.
  

Helpful tips:

• The easiest way to dispose of leaves is to simply mow them into the turf.
  
• Regular mowing during the fall will chop the leaves into small pieces and allow them to filter into the turf.
  
• Dry leaves mulch more easily and readily than wet leaves.
  
• Mulching leaves with a mower is much easier and less time consuming than raking, blowing, and/or vacuuming the leaves like we have done in the past.
  
• Mulching leaves disposes of the leaves without filling up our landfills and saves our municipalities thousands of dollars in disposal costs.
  
• Do not burn leaves because of our current burn bans and due to environmental pollution.
  
  
   
  
  
  
   

Aaron Patton, Turfgrass Extension Specialist

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