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Pre-harvest Dry Down in Small Grains with Glyphosate

Joel Ransom

Extension Agronomist - Cereal Crops

July 23, 2003

The early planted small grain crops in the state are beginning to mature. There are a number of herbicides labeled for pre-harvest use in small grains (except oats) for weed control and as harvest aids (see the 2003 North Dakota Weed Control Guide for a complete listing). Glyphosate, however, is the only labeled herbicide that can be used to aid in the dry down of the crop itself (as opposed to controlling and drying down weeds in the crop). Glyphosate is a systemic herbicide and takes from 7 to 10 days to effectively kill the growing parts of the crop so the dry down process is not immediately visible. Some of the potential advantages of using a pre-harvest dry down application of glyphosate are: allows earlier combining, eliminates the need for swathing, enables faster and easier harvesting and promotes more uniform ripening. Whether or not you will realize any or all of these potential advantages will largely depend on the climate and the characteristics of your crop at the time of application.

Consider the following when using glyphosate for pre-harvest dry down in small grains:

  • Glyphosate should only be applied when the crop has reached physiological maturity. Physiological maturity occurs at a grain moisture content of about 30%. At this moisture content the grain is in the hard dough stage and if you run your thumb nail across the kernel, the indentation will remain. Applying glyphosate before physiological maturity will reduce the yield and test weight of the crop and will almost certainly reduce its germination potential.

  • Because of the potential that glyphosate has when applied pre-harvest to reduce germination, do not apply it to fields that will be used for seed. Additionally, you should not use it in barley intended for malt.

  • The label requires that pre-harvest applications of glyphosate are made at least 7 days before harvest.

  • An added benefit of applying glyphosate pre-harvest is that it can control many perennial weed species. It is particularly effective in reducing infestations of Canada Thistle.

  • For rates and other information, refer to the label and the 2003 North Dakota Weed Control Guide.

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