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This is Dr. Nathan Mueller, your local agronomist with Nebraska Extension for Dodge and Washington Counties. As you begin to prepare for soybean planting, burndown herbicide programs are still be finalized and some are already applied.
Spring burndown of broadleaf winter annual weeds such as field pennycress, henbit, marestail, shepherd’s-purse, and tansy mustard can be a challenge depending on the size of the weeds, the weather conditions during and after spraying, and the presence of herbicide resistant biotypes.
Marestail is the only known broadleaf winter annual weed with herbicide resistance in eastern Nebraska. Marestail is native plant of Nebraska and biotypes exist that are resistant to glyphosate and ALS herbicides. Many of the marestail plants are still in the overwintering rosette stage and are much easier to control now prior to bolting. Control of marestail after the emergence of your soybeans is very challenging when biotypes are resistant to glyphosate and ALS herbicides.
Including 2,4-D, saflufenacil the active ingredient in Sharpen, or glufosinate the active ingredient in Ignite can help improve the control of these resistant biotypes. Sharpen does have a minimum soybean preplant interval ranging from 0 to 30 days depending on the rate and other tank-mix partners. 2,4-D ester has a preplant interval ranging from 7 to 30 days depending on the rate. However, Ignite does not have a preplant interval for soybeans and is a great option if you want to plant soon after spraying your burndown.
Several winter annual broadleaves such as henbit, the weed with purple flowers right now, can be harder to control with 2,4-D ester alone. Fortunately, glyphosate is usually every effective in controlling henbit. Also, tansy mustard and henbit both are a little tougher to control with ALS herbicides. Because all of this is a little hard to keep track of, I encourage you to get a copy of the 2016 Guide for Weed, Disease, and Insect Management in Nebraska. It is a great resource on evaluating herbicide options and it provides control ratings by weed species for various products and tank-mixes. A hard copy can be purchased at your local extension office or order online at marketplace.unl.edu.
For more information on winter annual weeds in Nebraska, call me at 727-2775 or visit our local website at croptechcafe.org. Know your crop, know your tech, know your bottom line. This is Dr. Nathan Mueller, your local agronomist with Nebraska Extension on KTIC radio.