Burndown Applications: Considerations for a Successful Spring

Mar 14, 2023

Many of our winter annual weeds have started to green up and grow during the latter half of March. Before long, they will begin to dramatically increase their vegetative growth before reproducing later in the spring. When the weather allows, 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. Many areas did not have a harsh winter to suppress growth of these weeds, so it’s important to not let them get too far along in their growth cycle. If left unmanaged this spring, weeds can get out of hand quickly and management of weed escapes may warrant a second herbicide application. Earlier burndown applications will ensure that we get control of our winter annual weeds while they are small, before they get to a growth stage that is much more difficult to manage.

When thinking about our herbicide options, make sure to use multiple effective sites of action. Additionally, pay attention to the air temperature at the time of application when managing emerged weeds. Burndown herbicides are much more consistent if the nighttime temperatures stay well above freezing and the daytime temperatures reach at least 50 degrees Fahrenheit. This ensures that the plant is actively growing and can 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. In addition, as we get closer to planting, a residual herbicide may be added to manage driver weed species, such as waterhemp. The residual herbicide to manage waterhemp will be more effective when applied closer to planting. However, if we delay our burndown application for too long, winter annual weeds such as marestail may become too large to be controlled. We need to find the best timing that ensures control of emerged weeds while being close enough to planting to get the best value from residual herbicides.

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Video: Spring 2026 weather outlook for Wisconsin; What an early-arriving El Niño could mean

Northeast Wisconsin is a small corner of the world, but our weather is still affected by what happens across the globe.

That includes in the equatorial Pacific, where changes between El Niño and La Niña play a role in the weather here -- and boy, have there been some abrupt changes as of late.

El Niño and La Niña are the two phases of what is collectively known as the El Niño Southern Oscillation, or ENSO for short. These are the swings back and forth from unusually warm to unusually cold sea surface temperatures in the Pacific Ocean along the equator.

Since this past September, we have been in a weak La Niña, which means water temperatures near the Eastern Pacific equator have been cooler than usual. That's where we're at right now.

Even last fall, the long-term outlook suggested a return to neutral conditions by spring and potentially El Niño conditions by summer.

But there are some signs this may be happening faster than usual, which could accelerate the onset of El Niño.

Over the last few weeks, unusually strong bursts of westerly winds farther west in the Pacific -- where sea surface temperatures are warmer than average -- have been observed. There is a chance that this could accelerate the warming of those eastern Pacific waters and potentially push us into El Niño sooner than usual.

If we do enter El Nino by spring -- which we'll define as the period of March, April and May -- there are some long-term correlations with our weather here in Northeast Wisconsin.

Looking at a map of anomalously warm weather, most of the upper Great Lakes doesn't show a strong correlation, but in general, the northern tiers of the United States do tend to lean to that direction.

The stronger correlation is with precipitation. El Niño conditions in spring have historically come with a higher risk of very dry weather over that time frame, so this will definitely be a transition we'll have to watch closely as we move out of winter.