ISSUE 1   May 5, 2005

SULFENTRAZONE REGISTRATION IN ND

The ND Department of Ag has just issued a Section 24(c) Special Local Needs (SLN) registration allowing use of DuPont Authority Herbicide on sunflower, dry field pea, and chickpea to control kochia. The supplemental labeling is available for download from the Departmentís online pesticide registration database:

http://www.kellysolutions.com/nd/pesticideindex.htm

and the NDSU Pesticide Programs page:

http://www.ag.ndsu.nodak.edu/aginfo/pesticid/pesticid.htm

Support should be given to DuPont and FMC for their willingness and hard work to gain these uses of Authority to address the Spartan supply shortfalls.

Additional sulfentrazone formulations will help address the supply problems with Spartan and ensure adequate supplies of sulfentrazone to meet most of the registered uses in North Dakota. 

**The Department has also declared a crisis Section 18 exemption allowing use of either Spartan Herbicide (the 75DF formulation) or Spartan 4F on flax. Use directions allowing these uses are described on the exemption. Please note that use of these Spartan products under the crisis exemption is limited to only 15 days. Therefore, the effective dates of the crisis are May 3 to May 17, 2005. These use directions can also be found on the Departmentís Section 18 page and the NDSU Pesticide programs page.

In summary:

Spartan DF =Use on any crop listed on the label.
May be used for a 15 day period on flax.

Spartan 4L = Use on snfl, field pea, and chickpea.
May be used for a 15 day period on flax.
Do not use on dry beans or potato.

Authority = Use on snfl, field pea, and chickpea.
Do not use on dry beans or potato.

Blanket = Uses for snfl, field pea, and chickpea may be registered by the end of the week.

**Sidenote - The Dept of Ag issued an news release last week stating several reasons why a Section 18 exemption for Spartan on flax will not be possible this year. No doubt of the large volume of phone calls from flax growers to the Dept of Ag describing their conundrum. In retrospect and without knowing the details of these recent happenings, one may summarize that if a group of growers make enough noise the Dept of Ag will finally do something. This Pest Report is not the place to make a rebuttal but a few things should be said in defense of the Dept of Ag which you will probably not see in print.

One - A different kind of Section 18 was approved (Crisis) for flax this year, meaning an unforeseeable catastrophe quickly occurred where no other remedy can solve the problem. See page 5 of the Weed Guide for an explanation between Emergency and Crisis exemptions. Time to develop a Section 18 exemption which normally takes 50-60 days, including time to prepare a request document, to obtain comment from U.S. Fish and Wildlife Service and other partner agencies, and to have EPA review the request could not be done. So by definition, having an Emergency Section 18 on flax from 2002 to 2004 does not validate the Crisis Emergency Exemption in 2005.

Two - When Jim Gray, Pesticide Registration Coordinator, NDDOA, approached the EPA to ask for their consideration of a ND Crisis Exemption on flax he was told they will NOT support it but they will not deny it AND IF IT WERE ANY STATE OTHER THAN ND, THEY WOULD DENY IT. What does this mean? It means ND has earned a good relation with EPA. It means the Section 18 packages we have submitted in years past were of high quality and we have NOT abused that registration process. It means the EPA has extended, in this one instance, some latitude. It does not mean this will ever happen again.

 

HOW DOES COLD WEATHER AFFECT HERBICIDE GLYPHOSATE ACTIVITY?

In short, the end result (weed control) will be the same as application in warm weather but the end result will take longer. Ideal temperatures for applying most POST herbicides are between 65 and 85 F. Weeds may be killed slower when temperatures remain below 50 to 60 F.

With exception of glyphosate, plants metabolize herbicides, but metabolism slows during cool or cold conditions, which extends the amount of time required to degrade herbicides in plants. There are no plants in the plant kingdom that metabolizes glyphosate, including Roundup Ready crops. So absorbed glyphosate will remain active in the plant until the herbicide is translocated to growing points after temperatures warm.

Several points could be made about the affect of cold weather on plants, such as, does the cold weather make the cuticle covering the leaf harder and less penetrable, does the herbicide on leaf become inactivated by sunlight, does much of the herbicide move through the cuticle until warm weather. Answers to these question may be hidden somewhere in published data.

What we do know about glyphosate is that growers should always add AMS. AMS facilitates absorption and translocation, deactivates hard water salts, and the ammonium in AMS makes glyphosate-NH4 in the spray droplet which is easily absorbed into the plant. The NDSU recommendation is AMS at a minimum of 1 lb/A or 4 to 6 lbs/100 gallons of water. As you know, this is different than what is stated on glyphosate labels. AMS at 4 to 6 lb/100 gal water will overcome almost all antagonism from ND hard water. There is some locations in ND where hard water can exceed 1600 ppm of hardness and requires AMS at 8.5 to 17 lb/100 gal water. Growers should know their water quality to determine AMS rate. I suspect more AMS is used by growers than is needed.

High quality surfactants should be added if the glyphosate label allows use. Use reputable adjuvants from our established adjuvant manufacturers. Do not fall for snake oils where claims of cutting herbicide rates by 50% is made.

Cold weather is a stress. AMS and surfactants are things growers can use to overcome the affect of stress.

Below freezing temperature may burn off top growth and desiccate plant tissue. Any plant material injured by freezing temperatures will not translocate herbicide. Application to new plant growth will be required for optimum herbicide activity.

Dust inactivates glyphosate. If glyphosate absorption is slowed during cold weather by hardening of the cuticle (which may or may not be true) then glyphosate on the plant surface may be susceptible to inactivation from dust especially if the wind blows, as has happened the last week or two. This applies also to slough water. Mud and soil sucked with water from sloughs will also inactivate glyphosate.

Time of day application studies show that activity of glyphosate if greatest when applied after 10:00 am and before 4:00 pm.

Do not use cut rates.

Glyphosate is not volatile nor deactivated by sunlight.

Use the lowest water volume (gpa) allowed on the label. Low water volume results in spray droplets with high herbicide concentration which results in greater absorption. Use drift reducing nozzles or drift reducing adjuvants to manage drift.

Richard Zollinger
NDSU Extension Weed Specialist
r.zollinger@ndsu.nodak.edu


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