Desiccation or Pre-Harvest Glyphosate Application - Frequently Asked Questions

 
 
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 Is there a difference between desiccation and pre-harvest herbicide application?
Yes, and the use is a matter of preference. True desiccants are harvest management tools that rapidly kill above ground growth of crops and weeds. This allows for rapid dry down and an earlier harvest. Desiccants will not give long-term weed control and any late moisture may cause both the weeds and the crop to start to re-grow.

Pre-harvest glyphosate application is generally used for perennial weed control. It can be used as a harvest management tool for dry down but the effects take much longer to appear. Pre-harvest glyphosate is a good tool for long-term control of perennial weeds such as Canada thistle, quackgrass, toadflax and dandelions.

When would I use desiccation or pre-harvest glyphosate?
Desiccation with products such as RegloneTM in pulses allows the crop to mature evenly for a faster harvest, which can reduce the risk of losing quality. Desiccation will not help immature seed to mature. Another reason for using Reglone TM in peas is for the control of wild buckwheat. Glyphosate does not work well in controlling wild buckwheat where RegloneTM does a better job.

Pre-harvest glyphosate provides control of perennial weeds, and can help to even out maturity and dry down cereal crops for straight cutting, however this will take time.

Can I desiccate or use pre-harvest herbicide if I want to use my crop for seed?
Desiccants such as RegloneTM on peas are registered for seed production. Glyphosate should not be applied to any crop that is to be used for seed production. Pre-harvest glyphosate applications can cause germination and possibly vigor problems in the spring. The seed may germinate but the seedling may be stunted and deformed. Seed may have good germination in the fall but poor germination in the spring. It is good practice to make sure you do a germination test again in the spring. Another thing to consider with pre-harvest is that maltsters generally reject seed that has been treated with pre-harvest glyphosate.

Can I use treated grain or straw for feed?
Both glyphosate and RegloneTM treated crops can be used for animal feed.

When should I apply glyphosate or RegloneTM?
Glyphosate should be applied when there is 30% or less moisture in the seed. In cereals the seed will be firm and with reasonable pressure your thumbnail will leave a dent in the seed. In peas, RegloneTM should be applied when peas are reaching maturity. This happens when the bottom 75 % of pods is yellow and the seeds are firm and loose in the pods. The tops pods on the plant will still be green, as will the seeds, although they may be starting to change color. The upper most seeds will be soft and will split into two pieces with little pressure. An important note with yellow peas is to make sure that most of the seeds have changed color from green to yellow before desiccating, as the color will not change once the plant starts to dry down.

Herbicide Selector

Prepared by Ag Info Centre, Alberta Agriculture and Rural Development.

 
 
 
 
For more information about the content of this document, contact the Ag-Info Centre.
This information published to the web on August 14, 2003.
Last Reviewed/Revised on April 23, 2015.