Tips and Tricks for preharvest Reglone & Glyphosate

In Northwest Saskatchewan peas are commonly desiccated or sprayed pre-harvest with glyphosate.  Reglone (Diquat – a group 22 product) is a desiccant that can help speed up the time to harvest.  On the other hand glyphosate (a group 9 product) is not a desiccant.  Glyphosate will kill the plants, but dry down rate is more dependent on weather – requiring hot temperatures and low humidity to dry down the plant.

When deciding when to spray Reglone or glyphosate on peas you must look across the entire field.  If the majority of the field has peas that match the following description it is time to spray.

  • The peas in the bottom third of the plant are detached and very firm when you bite into them (almost break your teeth firm).
  • The peas in the top third of the pods will split (not squish) when you squeeze them between your thumb and finger.
  • If you have yellow peas, the peas in the top third of the pods must be starting to turn yellow (or very light green) in order to avoid locking in the green color.

You may want to spray a bit on the later side with Reglone. If the field is ready to swath, it is likely ready to spray with Reglone.  When spraying Reglone be sure to use lots of water.  The optimum water rate is 15-20 gallons per acre. Sprayer pressure rates above 50 PSI will help ensure good coverage in a dense canopy.  Doubling up on surfactant rate may help the Reglone penetrate into the plant.  Also, spraying in the evening is the best timing for Reglone as it allows the chemical to be fully soaked in by the next day.  Remember, that with Reglone poor coverage equals poor results.

When spraying wheat and feed barley the timing of pre-harvest glyphosate is similar to swath timing – the hard dough stage.  If you press your fingernail into the seed and an imprint remains – it is ready.  Another method to determine proper spray staging for wheat and barley is to look at the peduncle (the part of the stem just below the head).  When the peduncle has changed from green to a yellow/brown color the crop has reached physiological maturity and can be sprayed.  Another way to check wheat/barley staging is to gently squeeze the kernels, if no water or milk comes out, it is in the dough stage and ready to spray.  With HRSW you can go a bit earlier – if you squeeze the kernels and just a drop of milk comes out (no water) you can go, but keep in mind this is a bit on the early side.  In my experience, this early timing has resulted in a nice red kernel, but if you go too early you may end up with shrunken kernels or lower bushel weight.  This method is used on a field by field basis and is only recommended after discussion weighing pros and cons with the client.

Above all remember that spraying glyphosate preharvest can affect the germination of the seed so caution must be taken. Glyphosate is a great choice where you have perennial weeds such as quack grass and Canada thistle.  If you have any questions, contact your local Cavalier Agrow Business Agronomist. Happy Spraying!


By Errin Tollefson, P.Ag