Utilizing a broad-spectrum fall (post-harvest) burndown can help reduce the soil weed seed bank by controlling winter annual and perennial weeds and offer several auxiliary benefits to row crop fields.

Beyond the goal of reliable weed control, a fall herbicide application can reduce host plants for pathogens such as Soybean Cyst Nematode (SCN), overwintering insects, and even diseases in warmer climates. It can also help maintain soil moisture in drought-stressed/arid climates, enable fields to be planted as soon as weather conditions allow, and help soil warming and drying in the spring, especially in no-till fields. The net result is more uniform crop emergence with fewer abiotic and biotic stressors.

Fall burndown applications start with identifying problem weeds for each field. Cool season (winter) annuals such as marestail, purple henbit, and Italian ryegrass are the primary targets of these applications. Depending on the geographic location of the field, the target weeds could change. These applications begin with a non-selective herbicide such as paraquat or glyphosate plus a residual herbicide to create a barrier for germinating seeds.

When targeting broadleaf weeds like marestail that can germinate over a long period of time, it is important to utilize a residual barrier that will be effective on small-seeded broadleaves. Some Group 14 herbicides, like flumioxazin, will accomplish this while adding some extra burndown power to the non-selective herbicide it is mixed with. If the target weed is a grass species, such as Italian ryegrass, a Group 15 herbicide will be needed to provide a residual barrier.

Poa or annual bluegrass can become a problem if left unchecked also. The addition of a Group 5 herbicide like metribuzin can be an inexpensive option that helps control bluegrass along with other broadleaf species such as common chickweed and purple henbit. Figures 1 and 2 shows the power of adding two residual herbicides (Anthem® Flex and Valor®) to a fall burndown. These applications were made in early December, and the photos were taken in early April.

Apply to emerged weeds post-harvest through early spring (avoid below-freezing temperatures and frozen ground).

 Adjuvants are recommended, especially when applying non-residual herbicides. Some glyphosate products have a built-in adjuvant and may not require additional surfactant.

 Metribuzin will provide burndown and residual activity. However, the residual value won’t be as great as with some Group 2, 14, or 15 products.

Be mindful of plant-back considerations and maximum use rates, especially if a pre-plant burndown and/or a post-plant PRE will also be used. For example, if using a flumioxazin product in the spring, a different product should be applied in the fall.