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Add Some Grit to Your Weed Control

Jeff Caldwell 08/15/2014 @ 9:40am Multimedia Editor for Agriculture.com and Successful Farming magazine.

If you're battling weeds in your fields, recent reports show that spraying them at this point in the growing season may not knock them down. So, what if you could knock them down . . . literally?

That's the approach behind a system being tested by USDA-ARS researchers in Minnesota. Targeted primarily at organic production systems, the "Propelled Abrasive Grit Management" (PAGMan) system replaces chemical with compressed air and "grit particles" to control weeds "around the bases of corn, soybean, and other row crops," according to a report from USDA-ARS by Jan Suszkiw.

The system, developed by ARS agronomist Frank Forcella, expels .5-millimeter-wide particles in a "cone-shape pattern" at a 100-pound/square-inch rate. That amounts to about 300 pounds of the grit particles per acre. This is the second year of testing for the system on silage corn, Suszkiw says. The results have been eye-opening.

"Field trial results from 2013 showed season-long weed control levels of 80% to 90% in corn using two treatments of the abrasive grit -- one at the first leaf stage, and the second at the three- or five-leaf stage of corn growth," he says. "Corn yields also compared favorably to those in hand-weeded plots used for comparison."

The process -- essentially sandblasting weeds into submission -- could be harmful to adjacent crop plants, too. Here's where timing comes in. Traversing a field with the PAGMan system should be done only when crop plants are large enough to survive the barrage of "abrasive grit.



The USDA-ARS system in testing currently features eight nozzles for four rows. (All photos courtesy USDA-ARS.)


"The crop plants escape harm because they're taller than the weeds during treatment and their apical stems (growing points) are protected beneath the soil by thick plant parts," says Suszkiw.

Adds Forcella, in an ARS report: "For the first few weeks of the growing season, weeds are relatively small, and that's when we target them with the grit."

The PAGMan system mounts to a tractor and comprises eight nozzles for four rows. ARS officials have used ground corn, or corncorb grit, for the abrasive material in the system. This makes it effective for "small annual weeds, like common lambsquarters, with high-speed particles of grit made from dried corncobs," says Suszkiw.

"We tried corn gluten meal and found it just as effective," says Forcella, who's based in Morris, Minnesota, in an ARS report. "The amounts necessary for controlling weeds were similar to those used to supply nitrogen to organic crops."



Here are some of the corn "grit particles" used in Forcella's system. They're propelled at weeds at 100 psi.  (Photo courtesy USDA-ARS.)


Looking ahead, the system will undergo more field testing before creators look to take it to market, an ARS report shows. That's both to further diagnose its effects on weed control as well as other implications for soil fertility, Suszkiw says.

"Ongoing field trials may foretell of the system’s potential to help organic growers tackle within-row infestations of weeds that have sprouted around the bases of corn, soybean, and other row crops," he says. "For organic systems, the grit selection can have more of an effect than just knocking down weeds."

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