Controlling Crop Weeds in the Spring

Many consider fall the best time to take on hard-to-kill weeds, especially perennials and winter annuals. For perennials, a post-harvest burn-off with glyphosate ensures chemicals get right down into the roots, preventing re-growth. Winter annuals are also better controlled in the fall, when they’re small seedlings.

If you didn’t do a post-harvest burn-off last fall, that doesn’t mean you’re out of chemical options in the spring. While applying glyphosate just prior to seeding in the spring won’t completely eliminate those stubborn dandelions or Canada thistles from your fields, it can help reduce competition for the incoming crop by providing top-growth control of perennials. A pre-seed burn-off will also eradicate annual weeds and can take out winter annuals before they get too big.

Jeff Strukoff, ADAMA Area Business Manager for Northeast Saskatchewan, points out that pre-seed burn-offs utilizing glyphosate and effective tank mix partners help crops get off to a great start by relieving early pressure from weeds like dandelions, narrow-leaved hawk’s beard, quack grass and cleavers, which in turn boosts the effectiveness of your weed control measures for the rest of the season.

So if you’re considering your weed control options for the spring, here are a couple of things to keep in mind that will help you get the most out of your pre-seed burn-off.

Pre-Seed, Post-Harvest

Timing is Everything

At the beginning of the season, there’s always the question of getting a pre-seed burn-off done in time before rolling out the planter, and a lot of that has to do with the weather. As Strukoff notes, glyphosate requires sunlight and a bit of warmth to work best, so it’s important to keep a close eye on the forecast and try to arrange your spray program around calm, cloudless days when it’s at least 5ºC outside. This will ensure translocation takes place fairly quickly and should maximize the effectiveness of your burndown.

For perennial weeds, the recommended delay between applying glyphosate and seeding is three days if it’s sunny and warm when spraying; if the weather is cloudy and cool when spraying, five days is recommended before seeding. When a pre-seed burn-off is targeting annual weeds, herbicides are sometimes applied as little as six hours before planting, but Strukoff maintains it’s a good idea to try to stay a day or two ahead to avoid having the sprayer catch up with the seeder.

Choosing the Right Glyphosate Partner

A pre-seed burn-off is a great opportunity to enhance your weed control with multiple modes of action. Combining glyphosate with another herbicide with residual action provides sharper control and helps limit the chances of resistance developing.

Strukoff notes there are a number of considerations when it comes to choosing the right glyphosate partner in your pre-seed burn-off. One is matching herbicides with crop type and then selecting products that best target the weeds present in your fields. For example, Strukoff says you can get your cereal crops off to a great start by teaming up glyphosate and HOTSHOT™, a combination of florasulam (group 2) and bromoxynil (group 6), to control a wide range of annual broadleaf weeds, including group 9 & group 2 resistant kochia, volunteer canola including glyphosate tolerant varieties, wild buckwheat and narrow-leaved hawk’s beard.

Another key consideration is field history. As Strukoff points out, growers should avoid using the same products over and over again on the same acres, and they should be also mindful of what chemistries they may use for subsequent in-crop herbicide applications when picking pre-seed tank-mix partners. By reviewing your cropping and weed control records and rotating active ingredients and chemical groups within your fields, you can further reduce the risk of resistance.

Strukoff acknowledges that growers sometimes choose glyphosate partners based on grower rebate programs offered by the big agri-chemical companies - but he maintains this isn’t always the best agronomic decision. Strukoff points out that alternative manufacturer products provide excellent value and are often the better choice when it comes to addressing a grower’s specific needs. For example, Strukoff notes some off-patent replacement products coming to market are packaged in increments that are more farm friendly, with 40-acre jugs taking the place of 25-acre jugs in some instances.

Getting the timing right and picking the right glyphosate partner are two ways you can maximize the effectiveness of your pre-seed burn-offs. For more information, see “ Pre-seed vs. Post-harvest: How to get the best perennial weed control ”.