Last fall, Tim Smith wanted to look at several products and their residual control of weeds. To make things as accurate as possible, he even left a check plot untreated. As of mid-April, the check proved that Smith — who manages Martin Farms in Holly Grove, Ark. — works land “that grows some big weeds that have to be killed off before planting.”
So, last fall, Smith put out some Roundup along with residual chemicals (Valor and Canopy XL) to control the growth of winter weeds.
“I don't like killing larger weeds and using high rates of herbicides. And it's just harder planting into fields with heavy weed pressure. But to spray in the fall, you have to wait until temperatures are consistently around 60 degrees or below. The reason for that is chemicals degrade with exposure to sunlight. So, when the days get shorter, the products last longer. When the chemical lasts longer, it means you'll get better residual control,” says Smith.
A lot of times, it's easier to make fall applications than spring applications. In the spring, “we're busy doing other things, and sometimes by the time you can do the spring application, the weeds have gotten big enough that they've gone to seed. By doing fall applications, you help prevent the weeds from going to seed.”
The Canopy XL treatment put out last November has provided very good residual control on early spring morningglories, cocklebur and grasses.
“We'll be able to go into that field with much more ease — it doesn't look like I'll have to do anything except plant. We may need to spot spray a couple of spots of johnsongrass as we go across the field planting.”
With the Valor field, Smith will have to go with a bit more Roundup — probably 24 ounces — to get rid of the weed pressure that's starting to build back up.
“I'm looking at about $15 per acre in herbicides — Valor or Canopy XL, either one — by spraying in the fall.”
There are differences between the two in terms of plant-back restrictions. With Valor, “there's a 60-day restriction on corn. You can put Valor on soybeans up until the plants start emerging.”
The plant-back restrictions on Canopy XL are much more restrictive.
“With Canopy XL, you're limited to planting soybeans back. There's something like an 18-month plant-back restriction on corn and cotton. So if you're looking to plant corn or cotton and you need a residual, you probably want to look at Valor.”
Next fall, Smith plans to work with another herbicide: Basis. It has limited plant-back restrictions.
“Hopefully, it works as well as Canopy XL,” says Smith. “The way I'm thinking now, everything we no-till next year will have a fall application of residual on it. It's that important to us.”