Burndown Success Combines Product & Practice

Burndown Success Combines Product & Practice
By Lyndon Brush, MFA staff agronomist and Andy Schmidt, MFA crop protection product manager

For a good burndown application, watch the weeds, think about the product and get there at the right time.

There are many factors that influence the uniform emergence of what you plant. And, whether you use no-till or conventional till to establish a field, the goal is simple—start with a clean field.

Seed-to-soil contact is important to get proper plant population, which gives seedlings a good start. Weed interference that hinders good seed-to-soil contact can cause reduced stands and possible yield reduction.

Given a head start, weeds can be more competitive for nutrients, water and light. Thus, preventing weed interference with young seedlings is critical in maximizing yields.

For no-till producers, it is critical to have the herbicide burndown program work much the same as a conventional tiller needs his tillage program to work. A weed-free field is always the goal. And regardless of the program, growers should realize that weeds not controlled through a burndown or tillage operation will generally require higher rates of herbicide during follow-up applications.

A successful burndown program consists of applying the correct herbicide based on crop to be grown, weed species and size. And it depends on ever-important timing of application. Any problems in this area can result in poor weed control and more trouble with weed interference at planting.

The purpose of a burndown program is to control the weeds present at the time of the application. That’s an obvious statement, but too often things get rushed, pushing planting and burndown too close together. Sometimes the burndown is applied just prior to planting. Sometimes the burndown goes on at planting or even after. While such timing may work at times, it can also lead to poor weed control and emerging crop stand issues.

Weeds emerge at different times through the growing season. Some weeds will emerge over a relatively short time frame compared to other weeds that, in the right conditions, will emerge over an extended time frame. Weed scientists use growing degree days to help predict when weed emergence will occur. Typically, early emerging summer annual weeds are giant ragweed, lambsquarter, sunflower, common ragweed, velvetleaf and giant foxtail. Right behind these come yellow foxtail, nightshade, cocklebur, crabgrass, fall panicum, waterhemp and morningglory, to name a few. The predictions assume some basic environmental conditions, but at times it may look like all weed species are emerging together.

Non-selective herbicides that can be used in burndown programs generally are either a glyphosate product or Gramoxone. Typically, what separates herbicide burndown programs for corn or soybeans is the use of other products in the tank mix. Corn no-till programs generally are still centered around using a glyphosate-based product (with or without 2,4-D), but most of the time an atrazine premix is also included in the application. In these cases, atrazine can also help provide some burndown characteristics. This approach works well where corn planting dates have been pushed earlier in the year. Such a burndown program is underway when weeds are small, which generally improves efficacy. With a rainfall event to activate the pre-emergent herbicide, weed control is off to an excellent start.

For no-till soybean production there are fewer pre-emergent herbicides, so burndown programs usually rely on glyphosate products. Because soybean planting occurs after corn planting, warmer temperatures allow for more weeds to emerge and potentially to be taller by the time the burndown is applied.

With no-till soybean fields, you probably hear reports about difficulty in controlling weeds like giant and common ragweed, lambsquarter and marestail. Even early emerging waterhemp can be a problem in some no-till fields. While all these weeds can be controlled with the burndown program, if you miss them, control becomes much more difficult. You will often see that late applications of glyphosate won’t provide satisfactory results for weeds that have already been sprayed once but not completely controlled. Adding 2,4-D to the burndown tankmix of glyphosate for such weeds can help. Remember that you may need to increase rates if weeds get too tall, especially for glyphosate. Always refer to the label for the correct weed height and recommended herbicide rate.

Some people may argue that by adding 2,4-D in the tank mix you have to wait too many days before planting the crop. While that is true (when applying 1 pint per acre of LOV 2,4-D, you need to wait to plant soybeans for 7 days), it is also a way to make sure the burndown program will control the weeds that are present prior to planting.

Other soybean pre-emergent herbicide products may help in the burndown. Authority First, Sonic, Canopy, Sencor, Scepter and Valor are a few options. Keep in mind that not all soybean-based pre-emergent products have activity in the burndown program. Some that don’t are Dual, Intrro, Outlook and Prowl. The goal for adding these products in the mix is to provide control on weeds that have not yet emerged.

So take a close look at present weeds, size and timing as you prepare to apply a burndown. To offer broad-spectrum control of existing weeds, a program containing a glyphosate-based product along with 2,4-D is the place to start. Burndown programs that use Gramoxone also can do the job, especially with the addition of crop oil as an adjuvant.

With any program, the trick is to apply the correct product in a timely fashion. Easy advice in such a hectic time, but do so and you will be off to a clean and successful start to the growing season.

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