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Blasting Weeds to Oblivion

Grit applicator fires weed-and-feed bullets

Frank Forcella was surrounded with apricot pits—a seemingly useless collection of fruit stones saved in an endless line of 5-gal. buckets. Apricot trees don’t fare well in the cold of Minnesota, but Forcella scratches out a hobby harvest each year and hit a bumper crop in 2007. More apricots; many varieties; and a massive jump in his pit bucket mother lode. What to do with a never-ending pit collection?

Commercial fruit processors often grind a portion of shell pits for use in commercial sand blasting as a soft grit. As an USDA–Agricultural Research Service research agronomist, Forcella believed organic grit might be an effective weed killer. His determination to break from conventional thought has resulted in a four-row grit blaster capable of obliterating weeds.

Dan Humburg, ag engineer, South Dakota State University, and grad student Corey Lanoue built the grit applicator, which is hauled by a tractor. “Typically, when you’re sandblasting, operations are power hungry. We tried to maximize efficiency and turned compressed air into abrasive velocity,” says Lanoue, now a design engineer with Vermeer Manufacturing.

With four rows and eight nozzles firing grit at 100 lb. per square inch, Forcella runs the system through corn field plots twice each season. Each nozzle blasts a 4" band, first when corn is 4" to 6" high at the one- to three-leaf stage and second when corn is 1' tall at the five-leaf stage. His field trials show 80% to 90% season-long weed control. In addition, Forcella has successfully tested a weed-and-feed method for organic growers, using cottonseed and canola seed meal. Essentially, he’s killing weeds by spraying high-velocity fertilizer.

What about crop damage? “One of the things we were worried about was disease. Make a hole in a crop plant and open a door to crop disease. However, there are no problems because the crops aren’t hurt at all. The grit is aimed at the base of the corn plants and nails small weeds. Weeds must be below a couple of inches or the system won’t work,” Forcella notes.

When a broadleaf weed—such as Palmer amaranth—is hit with grit, the stem is severed, and the root cannot regrow. The root system withers due to a lack of photosynthesis. However, when grasses germinate, the growing point is still below the surface. Blasting grit eliminates the leaves, but the grass continues growing. Specific grasses must be hit at least twice to kill them, Forcella says. “We’re going over twice anyway to compensate for early germinating and late-germinating broadleaf weeds,” he adds.

Costs to run the grit applicator system range from $50 to $100 per acre. “A conventional grower doesn’t want to spend over $50 per acre for weed control, but that’s pretty good for an organic grower,” Forcella says. 

Crop changes might open doors for the weed blaster—especially as herbicide-resistant Palmer amaranth spreads. “When I see pictures from the South of workers chopping Palmer and throwing it in carts, it looks like images from 100 years back. Where there are no reliable alternatives, a grit applicator could work,” he adds.

From apricot pit to grit applicator, Forcella has found success in out-of-the-box ideas. “As a weed scientist, I wondered if you could kill weeds with grit. It’s certainly a crazy idea, but I couldn’t shake the thought. This is small-scale, but it works.” 

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