By Nick Dunn

Pre-harvest tools like desiccants and harvest aids can be valuable for speeding up dry-down and reducing weather risk. But timing, method, and market acceptance are critical; the wrong choice can cost you grade and marketability.

Most desiccants are contact products meaning they only dry down the green plant tissue they touch. If sprayed too early, you lock in green, lightweight, or shriveled kernels. Too late, and there’s little benefit. In cereals, the right stage is the hard dough phase, when kernels resist a thumbnail and moisture is about 30% or less. For peas, 75–80% of pods should be brown, with lower pods rattling. In flax, the crop should be about three-quarters brown, while in canola, 60–75% of seeds on the main stem should show color change from green to brown, black, or yellow. Following these benchmarks protects seed quality while still giving the crop a dry-down boost.

Glyphosate is often discussed at harvest, but it’s not a true desiccant. The systemic herbicide moves inside the plant and can carry into the seed if applied before 30% seed moisture, reducing germination and raising residue concerns. Many buyers, especially for malt barley, peas, and some wheat classes, reject glyphosate-treated crops. True desiccants such as diquat, saflufenacil, glufosinate, flumioxazin, and carfentrazone act on contact only and do not move into the seed. Buyer standards do vary, and some markets won’t accept crops treated with desiccants at all. Know before you spray!

Residue concerns go beyond local rules. Export markets follow maximum residue limits (MRLs), which may differ from Canadian standards. Even if a product is registered, exceeding another country’s limits can result in rejection at port. Spraying at the correct crop stage, using only registered products, and checking with buyers beforehand reduces this risk and helps protect your market access.

Good coverage is one of the biggest factors in successful desiccation. Because these products only work where they touch, high water volumes of at least 20 gallons per acre are recommended. Skimping on water often leaves green patches that slow down harvest. Weather also plays a role. Some desiccants work best under bright sunlight when plants are actively photosynthesizing. Cool or cloudy conditions reduce effectiveness, so choosing the right day can make a real difference.

How the product is applied also matters. High clearance ground sprayers usually deliver the best coverage, but aerial spraying by plane can be useful when fields are large or too wet for ground equipment. The downside is increased drift risk and less ability to hit recommended water volumes. Mechanical methods like swathing remain valuable in certain crops, particularly canola, where cutting and windrowing at the right time can even out maturity and reduce shattering losses.

This year in Flagstaff County, crops emerged fairly evenly. That reduces the pressure to rely on desiccants and gives growers the option to let crops dry naturally. Even so, unpredictable fall weather may still push some toward chemical or mechanical aids to protect yield and avoid delays.

Nick Dunn is Flagstaff County’s Agricultural Fieldman. He can be reached via email at: ndunn@flagstaff.ab.ca or by phone at: 780-384-4138.