• Early burndown applications provide an opportunity to manage winter annuals before they become more difficult to control
• Adding a residual herbicide to a burndown has value but shouldn’t be the only application for summer annual weed control
• Always read herbicide labels to determine if a plant back restriction is in place for each herbicide used
• While a residual may be beneficial in the burndown trip, another residual should be applied closer to planting to aid in residual control of summer annual weeds like ragweed and waterhemp

As February comes to a close, we can reflect back to a year ago, and temperatures, and field conditions are complete opposite. Once the weather does break, and field operations commence, Anhydrous ammonia and dry fertilizer applications will be on the priority list. However, let’s not forget the importance of timely herbicide applications, and the value that a spring burndown can bring when managing tough to control weeds.

With the fluctuating fall conditions across much of the territory, winter annual weeds have had a head start in some geographies while in others weed development may be much slower. While the harsh winter may have suppressed some of the growth of these weeds, its important to not let them get too far along in their growth cycle. If left unmanaged this spring, there is going to be a greater chance for weed escapes that will warrant a potential second burndown.

An early burndown application should ensure that we get control of our winter annual weeds before they get to a growth stage that is much more difficult to manage.When thinking about our herbicide options, make sure that we are using multiple effective sites of action.Another consideration would be the air temperature needed for good management of emerged winter annuals. Burndown herbicides are much more consistent if the nighttime temperatures stay well above freezing. This ensures that the plant is actively growing and will translocate the herbicide to the site of action.

Burndown applications that are combined with residual herbicides can help minimize the number of winter annual weeds that may emerge prior to planting.This may be a good option for growers who have a seedbank that contains many winter annuals or large seeded broadleaves that are early emerging. The residual herbicides that are typically effective on winter annuals also have activity on large seeded broadleaf weeds. However, keep in mind that even with a residual herbicide, an additional burndown may be necessary prior to planting.

When using burndown herbicides containing auxins as active ingredients be cognizant of the plant back restrictions on the label. Plant back restrictions are in place to prevent crop injury. If the plant back restrictions of an auxin herbicide will not be met, consider a different mode of action that doesn’t have a plant back restriction or has a shorter interval to planting.

Lastly, it is important to note that any residual herbicide we apply now should not be the only residual herbicide to be used prior to planting.We are nearly two months away from “normal” soybean planting time.An additional residual herbicide should be applied closer to planting to provide adequate control of summer annual weeds like waterhemp.

For more information on burndown and residual herbicide programs contact your local FS crop specialist.

Photo:  Marestail growth in Central Illinois field 4/2/2016