Scientist says: Stay on top of the weeds

AMONG THE benefits of no-till crops is weed control. By not stirring the soil, a field is likely to experience fewer weed flushes.

“Most weeds germinate within a couple of inches below the soil. If we take out the tilling, the number of flushes decrease. And any flushes you have tend to lessen with numbers. The second flush isn't as bad as the first, the third not as bad as the second,” says Ken Smith, Arkansas Extension weed scientist.

If you don't move seed, problems with weeds like nutsedge should lessen, says Smith. “In a conventional system, if you get nutsedge on your turn row, the next year it's worse and it just keeps getting worse. But with no-till, the weed seed isn't moved as easily,” says Smith, who spoke at the Monsanto Center of Excellence Field Day on Orelan Johnson's Coy, Ark., farm.

Something to watch for in no-till is a weed species shift. Farmers know their fields and within those fields they know what weeds are worst. The same weeds tend to show up year after year.

“But when switching to a no-till program, get ready because there could be a shift in species. Where pigweed once was a problem, you may see more of something else. With no-till you'll usually see more horsenettle,” says Smith.

When weeds shift, they'll usually move towards more perennials. Such weeds can be controlled if you're thinking about how to deal with them before it gets too late into the season.

“Be cautious because we're putting all our eggs in the herbicide basket. The cold steel basket isn't one to reach for any longer,” says Smith, who is based at the Southeast Arkansas Research and Extension Center in Monticello.

“Fortunately, we have the herbicides to no-till a crop. Back when Treflan® came out, everyone said ‘This isn't a good deal. Nobody is going to use something that has to be incorporated.’”

Well, that turned out to be false, says Smith, and opinions change. Now the view is that anyone thinking they can make a crop without incorporating a yellow herbicide needs to rethink their position.

One thing Smith wants to make crystal clear: timing is critical — especially in no-till. You can't catch up to weeds in no-till. You can't run out in the field with a cultivator that'll help catch up. So it's absolutely critical to stay on top of weeds.

“I had a farmer come up to me yesterday and ask how big morningglories could get and Staple still be effective. At this time of year, if someone is asking that question, the morningglories have already grown too big.

“I asked how big they were. He said they were running on top of the cotton. Well, he's not in a Staple burndown program now. He got behind and it's just too late to catch up without great expense.”

If you're on time, Smith says, no-till isn't just a good system, but an economical one.

So what works in no-till cotton?

  • Roundup® plus 2,4-D at burndown works well depending on spray cut-off dates. Plant clean and stay clean.

  • Roundup over-the-top at one leaf and four leaf.

    “What's the most critical time for weed control in a cotton crop? Between four leaf and post-direct. If you have to wait until 7 or 8 leaf before getting a good post-direct, that time between 4 leaf and 8 leaf can provide easy opportunities for weeds to spring up.”

    So spray Roundup whenever you need to, says Smith.

  • Roundup plus residual at layby.

    “This program works. I've got plots with this that are incredibly clean.”

  • Burndown (2,4-D) plus Roundup

    “If a field has a lot of pigweed, I'd probably lean a little more toward Dual® pre,” he notes. “If the field is sandy, don't put Dual down pre but early post.”

  • Prowl® pre-emergence.

    “Lots of farmers are using Prowl pre. If it works, great. We don't use it because sometimes it causes brittle stem.”

Above all, when growing no-till, stay atop the weeds, says Smith.

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