Diquat provides a quick, uniform dry-down of green material to aid in evenness of plant material at harvest. According to Winfield Canada’s August 1, 2025 article, Start your Engines: Ready, Set, Desiccate, Diquat is a Group 22 herbicide and works by breaking down cell walls – essentially giving the plant a flat tire – making the plant ‘leaky’ allowing water to escape. Unlike glyphosate, however, diquat does not kill the plant, it merely dries it out. If rainfall happens, or the crop is left in the field too long after the diquat application, re-growth will occur. However, a key benefit of diquat is that it does not affect germination of the seed, making it a safe choice for pulse applications where saved seed is part of next year’s production plan.
Here are some strategies for successful diquat application:
Water Volume
All diquat products are contact herbicides and therefore water volume is important. Labels usually call for 24 gallons per acre as a minimum water requirement. To have great coverage – water volume matters. More water will help get coverage deeper down into the crop for more consistent results, particularly in dense canopies.
Surfactant
The addition of a non-ionic surfactant (NIS) is required for most diquat products registered for Western Canada. We want to decrease the amount of droplets that dry on the leaf because as soon as they dry then can no longer be absorbed by the plant.
Water Quality
Diquat is affected by the presence of particles in the water. If using a dug-out, ensure the water is clear and clean. Manage your water source to eliminate algae and find an alternate water sources to use with diquat if you suspect the water is contaminated.
Coverage at the Base of the Plant
Ideally, you want full plant coverage of plants from top to bottom. While not a weed control product, diquat will dry down existing weeds that may be hiding under the crop canopy. Even in a clean field, getting diquat to the base of plants is vital for a thorough dry down. Penetration to the plant base can be more successful with the addition of products that offer drift control to keep the spray on target but also alter droplet size to eliminate fine droplets and get spray penetrating to the base of a thick canopy.
Droplet size is an important factor for coverage. Use droplets that are medium to slightly coarse to keep the spray on target and getting into the canopy.
Application Timing
There is more to application timing than just the stage of the crop. When it comes to diquat, time of day is also a huge factor for success. Diquat is best applied in low-light conditions such as in the evening or overnight, so that the product can be absorbed properly into the plants before sunlight activates it.