Soybean Pest Beat: Get rougher and tougher when going after marestail.
Sep 09, 2020
I’m still struggling with marestail breaking out late in beans and making harvest difficult. Someone said I should spray fields going to beans this fall for marestail. Is that good advice? If so, what should I spray?
The Indiana certified crop adviser panel answering this question includes Steve Gauck, regional agronomy manager for Beck’s, Greensburg; Andy Like, independent crops consultant, Vincennes; and Dan Ritter, agronomist with Corteva Agriscience, Rensselaer.
Gauck: Fall spraying in most areas is an effective way to control the fall-germinating marestail. This makes planting and weed control more effective in the spring.
If the late-breaking marestail is larger marestail that your burndown or post-emergence application didn’t control, then fall spraying is a good option. If the late-season breaks are coming from your preemergence herbicide not holding and allowing escapes, then I would start to look at a more powerful preemergence herbicide program and layering in a residual at early post timing for longer-season control.
Weed spectrums are changing, and you need to start planning stronger preemerge herbicide programs with residuals. Start thinking about post herbicides as more of a rescue or cleanup treatment instead of as the main weed control system. In all herbicide treatments, you need to apply multiple modes of action, and even change those modes of action every few years.
Like: Fall spraying will control fall-emerging marestail only. It sounds like you have spring-emerging marestail that survives your burndown pass or comes up after you have burned down weeds. I would increase the robustness of your burndown pass if you are missing them, and add an effective residual to keep new marestail from emerging. Remember that most populations of marestail are glyphosate- and ALS-resistant.
Ritter: A fall burndown can be a useful tool for the control of many winter annuals, including marestail. This also can help dry out soil next spring and improve planter operation by eliminating weedy areas.
When it comes to a complete management system, I may refer you to takeactiononweeds.com. It is a collaborative university website that has many suggestions for control on marestail. Generally, I would look at a 2,4-D product such as Enlist One in the fall in combination with a residual herbicide. Follow that with a solid herbicide program in the spring using a residual and post-applied chemistries.