Maintain a strong burndown program even with a late start

By Ryan McAllister, CCA, Team Sales Agronomist, Beck’s Hybrids

Farmers have been able to do little but watch as puddles and weeds grow in their fields this spring.

So far this spring it has been quite the challenge to get in the field to get any work done. Very little herbicide has been applied to no-till or minimum till fields. Some of these fields are getting lush with winter annual weed growth. However, winter annuals are not the only weeds that are beginning to emerge. I have seen giant ragweed, lambsquarter, marestail (which is a winter annual but also continues to emerge in the spring and summer) and morninglory, rearing their ugly heads as well. By the time most of our fields in eastern Indiana and Ohio are dry enough to get back on them with spray equipment, weed density and height could be more than what we have seen the past several years. I am concerned about the temptation that may exist to take 2,4-D out of the recipe because of its planting restriction or ignoring the planting restriction all together. Secondly, the temptation may exist to drop residual herbicides out of soybean burndown programs and simply burndown with glyphosate and 2,4-D or higher rates of glyphosate alone.

2,4-D planting restrictions and rates

The maximum ester rate that can be applied in the spring is 1-pound active ingredient per acre. For LV4 formulations, this equals 1 quart per acre. An application of 1 quart would require a 30-day planting restriction. An application of .5 lb active ingredient or 1 pint per acre for LV4 formulations, would require at least 7 days before planting soybeans. If additional 2,4-D is needed but 30 days is simply too long to wait, 2,4- ester products including E-99, Salvo, and Weedone 650 can be applied at a rate of 1 pound active ingredient per acre up to 15 days before planting. You might be asking yourself, does this planting restriction really matter? The short answer is yes.

What is the best soybean burndown program?

To answer that question, we have to consider which weeds are predominant in no-till/minimum till fields at this point in time. There are a wide variety of weeds (even summer annuals) emerging, but for the most part, dandelion, marestail, henbit, purple deadnettle and chickweed, have to top that list. For those of you that are not even considering a soybean residual but are more wondering about kicking out 2,4-D and increasing your rate of glyphosate, what are the consequences of that decision?

Glyphosate + 2,4-D verses Glyphosate alone

Glyphosate + 2,4-D has better control of lambsquarter, giant ragweed, mustards, shepherd’s-purse, dandelion and marestail. The most important thing for you to know is that glyphosate alone has virtually no control of either henbit or purple deadnettle. Both of these weeds are very invasive in most no-till fields this spring. The addition of 2,4-D still only gives you 70% to 80% control, but that is better than virtually none.

Glyphosate + 2,4-D + Residual verses Glyphosate + 2,4-D

The addition of spring applied residuals such as Sonic, Valor XLT, Envive, and Authority First, improve the control of purple deadnettle, henbit, and marestail over glyphosate + 2,4-D with no residual. Control of marestail goes to 90% to 100% with the addition of one of these residuals over glyphosate + 2,4-D at 70% to 80% control. Control of purple deadnettle and henbit goes from 70% to 80% control to 80% to 100% control with the addition of one of these residuals.

1.     To maximize soybean yield, post-emergence glyphosate applications must occur prior to weeds reaching 6-inches in height. This can best be accomplished by the addition of a residual to your burndown program to, in essence, buy you time.

2.     Applying glyphosate post-emerge when weeds are 9 to 12-inches tall can cause yield losses of 6% to 10% due to weed competition prior to control. Therefore, you must control them effectively in the burndown, as close to 90-100% control as possible.

3.     By attempting to avoid a planting restriction by removing 2,4-D, you could lose more money from weed competition by removing one of the key components of an effective burndown program.

4.     This is the best weed resistance management strategy. Multiple modes of action are always better than one.

Source for point 1 and 2: The Benefits of Preemergence Herbicides in Roundup Ready Soybean http://agcrops.osu.edu/weeds, www.btny.purdue.edu/weedscience.

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