Wheat and More….or Less
There is some good news in the battle on how to control weeds in stubble fields after harvest. And believe it or not, the ticket to clean post-harvest stubble may be simply the wheat variety you're planting.
A number of years ago we split a quarter of land into three different wheat varieties. Everything was the same-date of planting, seeding rate, fertility program, date of harvest. Everything was the same except for the variety.
Then a month or so after harvest while inspecting fields to see which ones we needed to spray for weed control, I came to that field…and practically fell out of the pickup when I noticed the first third of the field was as green as Ireland, but the next two thirds were as clean as a whistle. Right to the line.
Since we also grow rye and triticale, I see this all the time. There are few to any weeds in their stubble. These two crops are very effective in suppressing post-harvest weeds. And that is because of either a chemical effect known as allelopathy or because of a physical effect through plant competition or shading of the ground. Or it could be a combination of the two.
But it was the first time I had seen it with wheat varieties. It's way less common than with rye and triticale, but some wheat varieties are definitely hell on weeds.
Later in talking with University of Nebraska agronomist Gail Wicks, he also had a similar story to tell. He related to me that a southwest Nebraska farmer was out spraying his wheat stubble following the same field pattern he used when drilling the wheat the previous fall. Weeds, weeds, weeds. Then all of a sudden, there were no more weeds. The stubble was clean as a whistle.
It was like he hit a force field. He stopped the sprayer and just sat there for 5 or 10 minutes trying to figure out what had happened. Then he realized, this was the exact spot where he ran out of seed wheat last fall. And he had to switch varieties.
Also in talking recently with K-State Extension wheat specialist Jim Shroyer , he again told me the same story. This time it was from Decatur County, Ks. A farmer there took Jim out to a stubble field and asked Jim what he saw. Same thing. Weeds, weeds. Weeds. Then no weeds. And, of course, two different wheat varieties. Right to the line.
Back in Nebraska, Gail Wicks said because of this, they did a study rating wheat varieties on how effective they were on suppressing weeds. All agronomists do the same thing today in rating varieties for how well they do against leaf rust, strip rust and wheat streak mosaic and a host of other diseases. Interesting, one of the most effective wheat varieties in suppressing weeds was Turkey Red.
But also in the paper which was written about 20 years ago, the agronomists strongly encouraged wheat breeders to look for this trait. But they also conceded that the demand for wheats with such traits was minimized by availability of cheap and effective herbicides.
Well, times have changed…and with a vengeance. Today many farmers are ready to give up on all hopes of trying to control troublesome species like kochia because they have developed resistance to a number of commonly used herbicides. Today you can't control many of these weeds at any cost. So more and more farmers are having to resort to tillage for control of these post harvest weeds.
Realizing that, some wheat breeders are again taking another look at wheat varieties for control of weeds. Case in point is Allan Fritz at K-State. In a recent conversation with Allan, he mentioned they were now working with an Australian spring wheat which suppresses weeds through allelopathy. He plans to plant some of this variety this spring, then use extract of the straw to see if they can suppress weed germination.
"If the results warrant further study, we'll screen progeny from the crosses with this variety as well as work to map the trait so we can more it more easily," Fritz says.