Fall Glyphosate and Desiccation (Part 2)


By Harry Brook

Last week I talked about the appropriate use of glyphosate in the fall for perennial weed control. Now we’ll discuss what is the right timing to apply the glyphosate and actual desiccants.

The label states the crop should have less than 30% moisture in the seed when glyphosate is applied. What does that look like in cereals? The kernel should be in the hard dough stage, about 7–14 days before harvest. When using your fingernail to try and divide the kernel, the mark should stay on the seed. If applied when moisture content in the grain is more than 30%, the glyphosate is translocated into the grain and it will affect germination and other characteristics of the seed.

Before using glyphosate, prior to harvesting, check with your crop buyers, as there are more and more end users of the crop that do not wish to purchase crop that has glyphosate applied to it. Using glyphosate to control weeds prior to harvesting peas is still on the label of glyphosate products, but companies purchasing peas will not buy any peas that have been sprayed. Using any desiccant, they require the crop to be at a maximum of 30% moisture, the majority of pea pods (75%–80%) being brown and seeds in lower pods rattling loosely in the pods. With flax, the majority of bolls should be brown, around 75%.

There are other, more effective, products that are used as desiccants that dry down the crop quicker than glyphosate. These include diquat, sold as Reglone© and other products, saflufenacil (Heat©, most often mixed with glyphosate), glyphosinate (MP Good Harvest©), flumioxazin (Valtera©) and carfentrazone-ethyl (Aim EC©). You have to be careful with these as well as some end users don’t want any desiccant applied to the crop. When using glyphosinate ammonium, be aware it is only active under good growing conditions of sunlight and active photosynthesis. It doesn’t work well if weather is cloudy and cool.

Malt barley, peas and some wheat buyers don’t like any desiccant applied to the crop, which leaves you waiting for the entire crop to ripen, then straight cutting or using swathing to even out the crop. This increases the risks of weather damage to the crop. At least in Flagstaff County, most crops germinated very evenly and crops should be maturing around the same time.

Real desiccants are not translocated herbicides but are contact. This means coverage is vital to getting a good, even, crop dry down. To get good coverage you need to use high water rates, preferably 20 gallons per acre or better. You also have to be very careful judging the crop maturity as spraying too early will cause immature crop to downgrade the quality. That is why it is so important to know your crop staging prior to doing any desiccation or other, pre-harvest process.

As harvest approaches, use the various harvest aid tools appropriately. By pushing the envelop or using them other than as they are intended can lead to quality and crop value losses. You’ve invested too much in the crop to risk losing value now.

Harry Brook is Flagstaff County’s Agricultural Fieldman. He can be reached via email at: or by phone at: 780-384-4138.