Weather challenges, soil compaction and a late harvest may have prevented some Minnesota farmers from getting into the field to do fall tillage, which will affect the number of viable weed seeds come spring.
Even if you’re one of those farmers, you can still achieve good weed control.
If you did fall tillage
If you have fields going from soybeans to corn and were able to till your fields this fall, the first thing to do in spring is some light tillage with a cultivator to level off the field and eliminate any weeds that emerged early — usually lambsquarters or ragweed species here in Minnesota.
After that, within a couple of days of planting your corn, spray a residual preemergence herbicide over the top to help prevent any subsequent weeds from emerging.
If you weren’t able to do fall tillage
Maybe you weren’t able to harvest your corn until December due to bad weather or propane shortages that prohibited you from drying it, or you still have corn stalks standing in your fields.
The first thing to do in spring is use an aggressive form of tillage such as disking to incorporate some residue and eliminate any weeds that have emerged. After planting your corn, apply a residual preemergence herbicide.
Expect a higher weed seed bank
If you had prevented plant acres that were not able to be planted with a cover crop in 2019, there will likely be some weeds that grew, put on seed heads and produced viable seeds before you had a chance to till them under.
In this case, or if you had a cover crop planted on prevented plant acres that went to seed, be sure to eliminate those before you plant your cash crop. Finally, even if you did plant a crop in 2019, many fields had drowned-out portions where weeds were not shaded out by a growing crop.
Bottom line: Weeds flourished more than usual in 2019 because of abundant moisture, producing seeds and adding them to the weed seed bank. This makes applying a residual preemergence herbicide this spring especially important.
Wet spring, dry spring
If we have a wet spring in 2020 with delayed planting, weeds may be very tall by the time fields dry out enough for you to do tillage. This could prevent you from fully eliminating those weeds, as some may slip between the shovels of your field cultivator and continue growing. In this case, instead of just applying a residual preemergence herbicide, you may need to add glyphosate or other herbicide modes of action to the tank to remove any weeds that survived tillage.
If our spring is drier and planting begins in late April or early May, tillage should take care of any lambsquarters and ragweed species that have just begun to germinate. This will provide a clean seedbed for you to plant into, after which you’d apply a residual preemergence herbicide.
Don’t forget the big three glyphosate-resistant weeds in Minnesota: Common waterhemp, giant ragweed and common ragweed. Control them when they’re small with a residual preemergence herbicide to delay onset and slow growth. Then, if necessary, come back with some of the new 2,4-D or dicamba herbicide technologies now available in soybeans.
We’re all hoping for a more “normal” spring that will enable timely 2020 planting. Regardless of what we get, good weed management done as early as possible paves the way for clean fields and a strong start to the season. Work with your agronomist to plan your weed management strategy now.
Glady is a regional agronomist with WinField United in west-central Minnesota. Contact him at firstname.lastname@example.org.