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Serving: MN
tractor and sprayer Courtesy of WinField
A STEP AHEAD: The best weed management practices call for the right herbicide product on the right weed at the right time.

Make preemergence weed control a priority

Eye on Crops: Application timing is key.

By Mark Glady

Farm budgets are tight again this year. However, don’t let that keep you from doing a preemergence herbicide application.

Mark Glady head shot
Mark Glady


Preventing weeds from appearing in your corn and soybean fields — or at least controlling them when they’re very small — will save you time and relieve in-season stress while optimizing yield and return-on-investment potential at harvest.

Here’s why a preemergence herbicide should be an important component in your early-season weed control:

1. Fields were soaked in 2018. In my area of Minnesota, farmers got their corn and soybeans planted just fine in May. Then came the rains in June. And July. And August. Many farmers couldn’t get into the field to do anything. This is a perfect example of the value of preemergence herbicides. If a farmer didn’t use one last year, weeds got really big, really fast. With a preemergence application, the rain just kept activating herbicide ingredients, which worked well given the wet weather.

Bottom line: We don’t know how many good spray days we’ll get during the prime time for postemergence applications. It’s risky to rely on the weather to allow you to spray exactly when you want.

2. Weed seed multiplied last summer. Last year, 5- or 10-acre sections of fields got completely drowned out in some parts of Minnesota, killing crops. Without a growing crop to shade the soil, many weeds germinated that normally would not, causing those weeds to produce seed. As a result, we’ll be fighting a large weed-seed bank this season. Applying a preemergence herbicide this spring will help manage what will be a much higher potential for weeds than we had last spring.

3. You do conventional tillage or no tillage at all. Conventional tillage gets rid of a lot of weeds that germinate early in the season, such as ragweed and lambsquarters — as long as they’re small. After you plant and apply your preemergence herbicide with a residual, anything new that tries to germinate and sprout should be controlled. If you’re a no-till farmer, you’ll probably want to spray some glyphosate before your crop emerges. It doesn’t have any residual activity, but it will eliminate some of those early-season weeds that have germinated.

4. If weeds do emerge, they’ll be manageable. Preemergence herbicides are incorporated into the soil shallowly or rest on the surface. Most weeds need to be within an inch of the soil surface to germinate. And when they do, they’re usually between an eighth of an inch and a quarter of an inch long. When they come in contact with that surface layer, they’re much easier to eliminate.

5. Herbicide type and timing are key. Talk with your agronomist now about which weed species you had in 2018 to ensure you apply the right residual herbicide come spring. Most good preemergence herbicides do a nice job of controlling the problem weeds we have in Minnesota — most often waterhemp and ragweed.

For soybeans, make sure you’re having a conversation about which seed trait to purchase. If you’re planting dicamba-tolerant soybean varieties, timing will be especially important with the Minnesota Department of Agriculture June 20 spray cutoff date.

Also, if you plan to hire an applicator through the cooperative to apply your preemergence herbicide, make sure your retailer knows. Keep your agronomist and the retail location informed about which of your crops are getting planted, and when, so that application can follow as soon as possible.

It takes careful planning to apply your preemergence herbicides at the optimal time. It is worth it, though, to control weeds early for as weed-free a season as possible.

Glady is a regional agronomist with WinField United in west-central Minnesota. Contact him at WinField United is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.


TAGS: Crops
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