Effective, economical weed control
In a Michigan State University study, mechanical weed control cost half as much as chemical control.
The Wonder Weeder and similar tools deliver orchard weed control at less cost than chemical controls.
The Holy Grail that organic apple growers are looking for is an organically acceptable herbicide that acts like glyphosate or paraquat, but isn’t. Most chemicals that will do that, like vinegar, are expensive because it takes so much to achieve the result, and repeated applications are needed.
Dr. Matt Grieshop, organic pest management specialist at Michigan State University, isn’t sure the chase is all that important. In studies he started last year, mechanical weed control, using the Wonder Weeder and other tools like it, cut the cost of weed control to about half what chemical programs cost and gave similar results.
In his calculations last year, it cost $131.74 per acre to make two chemical applications a year to control weeds, while the Wonder Weeder, in four passes, did the job for $66.48—and a grower who built his own cultivator did it for $59.48. Grieshop’s estimates were based on a ten-year cost of ownership for a 100-acre orchard.
His initial conclusions are that cultivation provides a largely comparable level of weed management, reducing weed biomass and coverage about the same as do burndown herbicides—but not as much as preemergent herbicides. Some of his other data is very preliminary, but cultivation appeared to increase soil ammonium levels in June, when trees need nitrogen. (In some tests, it also increased it in August, when trees don’t need it.) The tillage incorporates organic matter, which releases nitrogen when it decomposes. He plans to follow organic matter levels to determine whether they build or decline with continued tillage.
Terminal growth was slightly less with cultivation, but within an acceptable range, he said. He does not believe the one- to two-inch-deep, shallow cultivation affects tree roots, and the action of the scraping shear bar is on the surface.
Cultivation may increase populations of beneficial organisms, he said, but that data is preliminary and not consistent trial to trial. Using mechanical cultivation does leave some vegetation in a narrow strip in the tree row, which can be hoed or mowed, or left as a refuge for beneficials.
The Wonder Weeder, manufactured by Harris Manufacturing in Burbank, Washington, has Lilliston rolling spider-type cultivator wheels that till a strip near the dripline and a stiff, steel shear plate that reaches under the trees and scrapes the surface. It is front-mounted so the operator can see what he or she is doing and make the correct steering responses so as not to snag trees, trellis, or irrigation lines. Irrigation lines would probably need to be up off the ground to exist compatibly with the tiller.
Grieshop wants to assess the impact of tillage on rodent populations, but expects voles will be less of a problem than when using mulches to suppress weeds.
Grieshop spoke during a session at the Great Lakes Fruit, Vegetable, and Farm Market Expo in Grand Rapids, Michigan, in December. •