Paraquat Mitigation Measures

Today’s material comes from an MSU Ag Alert regarding Paraquat Mitigation Measures, put out by Dr. Cecil Tharp, MSU Pesticide Education specialist. 

Photo by Kari Lewis

The EPA has approved several paraquat mitigation measures due to increased human health concerns.  Paraquat was first registered in 1964 in the US for weed control and crop desiccation; however, it is categorized as highly toxic through all routes of exposure by EPA where as little as one sip can be lethal with no known antidote. Many human poisonings through the ingestion of paraquat, either accidental or intentional, have been reported to EPA from poison control centers, product registrants, health agencies, environmental agencies and individual consumers. 

EPA has ordered the following measures to adequately protect applicators and the public.

1. Label changes emphasizing paraquat toxicity and supplemental warning materials.

2. Targeted training materials for paraquat users.

3. Closed-system packaging for all non-bulk (< 120 gallon) end use containers of paraquat.

4. Restricting the use of all paraquat products to certified applicators only.

In regard to the Targeted Paraquat Trainings, EPA is requiring all applicators who handle paraquat to take an EPA-approved paraquat training program when indicated on the new product label. EPA-approved paraquat training programs must provide information on: (1) paraquat toxicity; (2) a summary of the new label requirements; (3) consequences and examples of misuse of paraquat; (4) how to apply paraquat; (5) what to do in case of accidental exposure, and (6) appropriate handling, storage, disposal, and personal protective equipment requirements and instructions. The paraquat training program will be available via an internet link included on all paraquat end-use labels. All persons handling paraquat are expected to take the training every three years and retain documentation of successful completion.

At this point, we have not yet received specifics on the Targeted Paraquat Trainings, but we’ll be sure to keep you updated as we have more information.  The MSU Extension Pesticide Education program will continue to provide updates on that platform as we receive more information.   In the meantime, be sure to keep this on your radar.  For anyone needing a restricted use pesticide license or who would like one of their employees to become certified, you may test in your local Extension Office, or attend the training that will be held on April 17 in Conrad, watch for details on that.  Registration deadline is April 12, so register now to be sure to get on the list!

Post Harvest Kochia Control

Jesse Fulbright, MSU Liberty County Extension
 
With wheat harvest largely behind us, it is time to consider post-harvest weed control in wheat stubble if you haven’t already.  Weeds present before harvest have recovered from cutting and are growing in the absence of crop competition.  Any weeds that have germinated since harvest still have time left to cause problems.  Weeds should be controlled as soon as possible to prevent soil moisture use and seed production.  Controlling seed production to reduce weed populations next season is important when rotating to crops with limited options for in-crop weed control.  From a disease standpoint, early control of volunteer wheat and grass weeds is important to break the green bridge and reduce spread of wheat streak mosaic virus into next year’s crop. 

Kochia and Russian-thistle tend to be the most problematic species right now.  Consistent heat and moisture stress on the large weeds found this time of year make challenging conditions for achieving good herbicide efficacy, particularly with glyphosate.  The potential for glyphosate resistance in kochia and other weeds is an important consideration.  For this reason, glyphosate should be avoided entirely for post-harvest use if possible.  A notable exception to this guideline is when targeting grasses or volunteer wheat, where glyphosate is still a good choice when tank-mixed with other products.




If avoiding glyphosate entirely isn’t feasible, tank mixing with additional modes of action active on the target weeds is essential.  Another practice to improve herbicide efficacy is to spray only when temperatures are 80 to 85 F or less.  When temperatures rise above this, many plants start to shut down, which can reduce the amount of herbicide taken into plants.  When weeds are under drought stress, it may be best to wait for a rain or a period of cooler temperatures to restore active growth before spraying. 

Dicamba and 2,4-D are generally dependable options for broadleaf control alone, together, or tank-mixed with glyphosate or other chemistries.  Occasional reports of poor kochia control indicates that at least some low-level resistance to these herbicides may be present.  Often, this sort of emerging resistance is only expressed in plants under stress – typical conditions for post-harvest applications.  Again, tank mixing with multiple modes of action effective on the target weed is the best response.  Paraquat is a very effective contact herbicide with a unique mode of action.  Post-harvest applications are one of the best uses for paraquat, and a good opportunity to bring it into rotation for herbicide resistance management. 

While large, stressed weeds are generally less susceptible to herbicides than small, actively growing ones, contact products are less affected by weed stress and size than most systemic products.  If a period of dry, hot weather follows application, efficacy of contact herbicides is generally enhanced rather than diminished.  Contact herbicides kill only plant tissues they cover though, so good coverage is critical for performance.  

However it is accomplished, control of weeds in winter wheat stubble within a few weeks of harvest is important.  

Click here for more information about glyphosate resistant kochia: http://msuextension.org/publications/AgandNaturalResources/4602.pdf