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Weeds in wheeltracks

Chad Vroman noticed an unwelcome pattern in his soybeans last summer. The beans were clean except where the sprayer ran through his 15-inch rows. Wherever the sprayer wheels had run, he had lambsquarters popping through the canopy in late August.

It's probably no consolation to Vroman that this weeds-in-the-wheeltracks phenomenon is not unique. It's not unique to Roundup Ready soybeans. It's not unique to lambsquarters. It's not even unique to postemergence herbicides. It just seems more noticeable the past couple of years.

There's no one readily identifiable cause -- and certainly no single or simple solution. It may not even be a problem every year. In some cases, the weeds may be surviving the initial herbicide application, while in others you may be seeing new flushes of weeds.

Last year there were weeds in wheel tracks throughout Illinois, says Aaron Hager, Extension weed scientist at the University of Illinois. "We heard more reports in the northern part of the state, but we can see it occurring in virtually any part of the state we travel to," Hager says.

Chad Vroman noticed an unwelcome pattern in his soybeans last summer. The beans were clean except where the sprayer ran through his 15-inch rows. Wherever the sprayer wheels had run, he had lambsquarters popping through the canopy in late August.

One school of thought is that these wheel track weeds survive the herbicide application because the wheel traffic stresses the plants to the point where they are not actively taking in and translocating the herbicide that was sprayed on them.

Another possible explanation for these wheel track weeds is that they may be new flushes rather than escapes. In some cases, such as when the soil is loose and fairly dry, the wheel traffic can firm the soil enough to create a good environment for germinating a new flush of weeds.

There have been a number of suggestions for setting up a sprayer to avoid problems with dust and survivors (see sidebar at right). Some claim having the boom on the front of the sprayer will reduce problems with dust tying up the herbicide. Others suggest using a larger nozzle (making sure you stay within label rates) over the wheel tracks.

Wheel track weeds may be hurting your pride more than your yields, the weed scientists say. That's especially true if they are new flushes that germinate after your initial spray.

I had the same conversation with a custom applicator. He told me the reason I had weeds in the wheel tracks was because my Willmar has the spray boom in back and that is why he uses a Hagie. I noticed fields he sprayed this year are showing the wheel tracks, while my wheel tracks are clean! Go figure. -GreaTOne_65

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