Post-harvest weed control, or fall pre-seed, offers the benefits of spring pre-seed with the added workload and time management payback you gain in the spring.

Several products are registered for fall pre-seed weed control that, tank mixed with glyphosate, cover a wide spectrum of weeds. Most important in fall are winter annuals and dandelion. Canada thistle shouldn’t be ignored either. Winter annuals left unchecked reduce soil moisture and nutrients throughout fall and in the spring, when they resume growth. Dandelion, with its large root system, is difficult to control; however, research has shown that fall is the best time to tackle this persistent weed. Cooler conditions lead the plant to translocate energy to the roots, carrying the herbicide along and increasing the likelihood of complete control.

Once the soil cools in the fall ( ≤ 10 C), certain products offer control that extends to spring. The breakdown of the active is halted over the winter, and early-emerging, susceptible weeds are controlled when activity restarts in spring. This is especially important for volunteer canola, which emerges in flushes in fall and spring and can be high in numbers.

Generally, fall pre-seed sets you up for spring. Additional control may be required due to high weed populations, delayed seeding or the effectiveness of the chosen product.

Bottom line, plan ahead for fall weed control as part of your post-harvest workload. You will thank yourself come spring and your crops may deliver bigger results.

Kelly Bennett is the category leader for herbicides in Western Canada at Corteva Agriscience.

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This spring, pre-seed weed control is especially important for starting crops off right and maximizing yield potential. However, due to weed density and diversity, high-performing combinations with glyphosate will ensure control of all weeds present, while also delaying the onset of glyphosate-resistant weeds.

For farmers with harvest to complete, planning ahead or utilizing custom spraying will be important to ensure pre-seed weed control is feasible. Products offering a period of extended control will be preferred for preparing fields to seed cereal crops to manage the higher potential pressure of flushing volunteer canola. If time is short, prioritize the fields with the most weeds first.

Better moisture conditions should lead to more routine in-crop weed control in 2020. Lower wild oat pressure in 2019 led to more use of lower-cost, lower-performing graminicides. Despite smaller populations, escapes were allowed to go to seed. Higher-performing products will provide better results, especially with the higher wild oat populations expected in 2020. Broadleaf weed populations are also expected to increase. Scouting for size, density and numbers of species will be important to ensure the right product is chosen.

Herbicides play a critical role in weed control, but it is important to remember that practising multiple strategies leads to the best results. Good agronomic practices that lead to a denser crop stand will ensure partially controlled or subsequent flushes of weeds are suppressed, making your overall weed control program more effective.

Kelly Bennett is the category leader for herbicides in Western Canada and Rory Degenhardt is the integrated field sciences research leader for Canada at Corteva Agriscience. Both are based in Alberta.

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