County Agent News

Dan Folske

May 10, 2010

NDAWN WEATHER INFORMATION

            NDAWN weather information is available for producers.  Details can be accessed on the internet at http://ndawn.ndsu.nodak.edu  This web service is always 24 hours behind current conditions, however up to the hour information can be obtained by calling the stations direct.  Keep in mind that the current conditions seem to be 1 hour behind  (they are in fact accurate) – NDAWN does not make the adjustment for daylight savings time.  Local numbers are:

            Bowbells          701-377-4455

            Crosby             701-965-4455

            Mohall             701-756-6132

            Berthold          701-453-3630

            Minot              701-839-2760

            Bottineau        701-243-6325

Always hang up using the * star key 

Note: These temperatures are several degrees cooler than the temperatures from two weeks ago!

Glyphosate Burn-Down Tips – Pre-plant or pre-emergence glyphosate applications to control weeds are becoming standard practice with the majority of producers now using some form of direct seeding. Following are a few recommendations to get the best weed control from glyphosate applications.

First, with so many different glyphosate products on the market with a wide range of acid equivalent (ae) concentrations make sure that you are applying the correct rate of the product to achieve desired ae per acre.  With glyphosate, rates should be based on the ae per acre rather than on the active ingredients (ai).  The ai of glyphosate is the weight of both glyphosate acid and the weight of the salt formulated with the glyphosate molecule. The salts that are formulated with glyphosate molecule do not contribute to weed control. The ae of glyphosate is just the weight of the glyphosate without the weight of the salt.  Tables can be found in the current NDSU Extension Weed Control Guide which will help to understand the relationship between ai and ae. 

Second, 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 herbicide absorption.  Time of day application studies show that activity of glyphosate if greatest when applied after 10:00 am and before 4:00 pm.  While that may not always be possible or practical, try to at least target applications between 8 am and 8 pm.  Spraying early in the morning when foliage is wet with dew may reduce weed control.  Dew on leaves dilutes spray droplets and negates the effect of low spray volumes at application.  For best results, allow at least 6 hours rainfast period for all glyphosate formulations regardless of label rainfast recommendations.  Humid and moist conditions increase glyphosate activity and conversely, dry conditions can lower activity. 

Third, always add ammonium sulfate (AMS) to glyphosate.  AMS enhances absorption and deactivates hard water salts.  The ammonium in AMS reacts with glyphosate to from glyphosate-NH4 in the spray droplet.  This is desirable as glyphosate-NH4 is more readily absorbed by plants than other ionic forms of glyphosate.  Research at NDSU has found that the addition of AMS increases weed control under good and adverse growing conditions and with or without antagonistic salts in the water.   

Research has shown generally less weed control when “Water Conditioning Agents” or AMS Replacement adjuvants are used instead of AMS.  When using replacement products, use only those known to contain at least 4 lbs of AMS/100 gallons of water at their recommended rates. 

Fourth, spraying during cold weather.  Most herbicides require an actively growing plant in order to work effectively.  Ideal temperatures for applying most post-emergence herbicides are between 65 and 85 degrees.  Speed of kill may be slow when temperatures remain below 60 degrees.  Glyphosate, unlike most herbicides, isn’t metabolized by plants, so if it is absorbed, glyphosate will stay in the plant and will begin “working” once conditions warm to the point where translocation within the plant resumes. The end result is that glyphosate applied during cool and cold weather will kill weeds, it will just take longer.  However, it certainly doesn’t hurt to wait a couple of days following really cold periods before spraying to allow the weeds a chance to recover and resume active growth, if you have that option.  If temperatures do get cold enough to freeze emerged plant tissue, then allowing recovery times is necessary as plant material injured by freezing temperatures will not absorb and translocate the herbicide.  Cold weather is a stress. AMS and surfactants are things growers can use to overcome the affect of stress along with using full labeled rates.