August 7, 2003

 

Glyphosate for Pre-harvest Dry-Down in Small Grains

There are a number of herbicides labeled for pre-harvest use in small grains (except oats) for weed control and as harvest aids. However, glyphosate is the only labeled herbicide that can be used to aid in the dry-down of the crop itself, according to Joel Ransom, North Dakota State University Extension agronomist. But be sure to read the label to make sure it is registered for pre-harvest dry-down, Ransom advises.

Glyphosate is a systemic herbicide that takes from seven to 10 days to effectively kill the growing parts of plants so the dry-down process is not immediately visible.

Using glyphosate as a pre-harvest dry down has some potential advantages, Ransom says. It:

• Allows earlier combining
• Eliminates the need for swathing
• Enables faster and easier harvesting
• Kills late season tillers.

"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," Ransom says. "But if the crop seems to be drying-down uniformly and there are no serious weed problems, it will definitely be more economical not to use glyphosate before harvest."

Kirk Howatt, NDSU Department of Plant Sciences weed control specialist, has been researching the use of glyphosate for the past few years. "The fact that growers can straight combine their fields is a big benefit when using glyphosate," Howatt says. "It means one pass through the field instead of two. Any time you lay grain on the ground; there is the chance of a heavy rain causing sprout damage in the windrow."

For his research, Howatt used different formulations of glyphosate alone and with other products that are promoted as enhancing dry-down. "One of the problems we’ve had is we haven’t consistently shown growers will get in the field sooner. There is literature that supports it and some that doesn’t. However, growers will have a cleaner field."

Ransom and Howatt say there are some procedures to follow when using glyphosate for pre-harvest dry down.

• Glyphosate should only be applied when the crop has reached physiological maturity. Physiological maturity occurs at a grain moisture content of about 30 percent. At this moisture content the grain is in the hard dough stage. An indentation should remain when you run your thumb nail across the kernel. Applying glyphosate before physiological maturity may reduce, depending on the year and how early it was applied, the yield and test weight of the crop and germination potential.
• Because glyphosate may reduce germination, do not apply it to fields that will be used for seed.
• Glyphosate should not be used in barley if it is intended for malt.
• The label requires that pre-harvest application be made at least seven 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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Source: Joel Ransom, (701) 231-7405, jransom@ndsuext.nodak.edu
Kirk Howatt, (701) 231-7209, kirk.howatt@ndsu.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu