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Glyphosate In The Fall

August 29th 2011

Producers are out spraying their cereal fields now to do a number of things.  The decision to spray with glyphosate is a good one in most cases.  The questions that need to be answered are important when it comes to the timing of the spray and the rates of product.  In this article, I will explain the factors that I am considering when I look at using this tool in the fall.

The first thing that must be understood is that using glyphosate in the fall is not a very effective tool for speeding up the dry-down of the crop.  The spray will kill the plant in four to seven days, but dry-down of the plants proceeds at a natural speed so weather is the main factor that must be considered when looking at days to harvest.

Glyphosate in the fall is an excellent weed control tool.  In fields where this tool has been used on an ongoing basis, perennial weeds like quack grass and Canada thistle have all but disappeared.  Winter annuals such as stinkweed and hawks beard can be significantly reduced with late fall spraying.  For ease of harvest, the green weeds that are present in the crop can be killed.  This has made the use of straight-cut headers on cereal crops much more practical. Green weeds make the grain more difficult to thrash.  Green weeds in the sample make the grain more difficult to store.  Removing weeds has an impact on the grain going to market as well as the grain in storage.

Using glyphosate can be a tool that will improve grades when a frost is imminent.  Frost on immature crops will downgrade the sample.  It can do this by affecting the kernels and causing damage to the seed coat.  Frost damaged wheat will be downgraded.  With late maturing heads in a wheat field, frost damage will be a factor.  In many years the use of glyphosate has brought wheat from a feed category to a number two grade wheat.  This is a lot of dollars in the grain grower’s pocket.  Also with frozen cereal grains, the bushel wheat of the grain will drop.  The lower bushel weights may cause a drop in grade.  Even without the drop in grade, light-weight cereal grains are more difficult to sell.

There are some down sides to using glyphosate in cereals in the fall.  The most important one to be aware of is the affect that glyphosate can have on germination.  Grain that has been sprayed with glyphosate should not be used for seed.  This seed lot could have a lower germination and reduced vigor.  Both these issues will create poor quality seed for next year’s crop. 

Fall applied glyphosate should not be applied to lentils or malt barley.  If glyphosate levels are detected in some markets, the crop could be rejected.  This rejection will cause long-term marketing issues if glyphosate is found in the seed of these crops.

If a cereal grain is sprayed too early with glyphosate, the kernels may not fully mature.  Green seed in a sample can down-grade a cereal, so the timing of application is critical.