A Wild and Woolly Idea

University of Minnesota Researchers say wool mats may give fruit growers an alternative to herbicides, and Minnesota sheep producers a market for their wool.

Some of the strawberry plants on Bill Jacobson’s fruit farm are tucked up in a soft, gray wool blanket. Bill, who grows 20 acres of strawberries and 15,000 apple trees, is helping scientists at the University of Minnesota test a new mulch made of abundant, renewable Minnesota wool.

Field trials at Bill’s White Bear Lake farm and at the U of M West Central Research and Outreach Center (WCROC) in Morris, Minn. — are evaluating how well wool mats control weeds in strawberry fields and apple orchards. Results to date suggest that wool is a good weed barrier with additional horticultural advantages. The research is sponsored by the Agricultural Utilization Research Institute and is attracting strong interest from two groups of growers: strawberry farmers who face new restrictions on herbicides and sheep producers who seek new uses for wool.

Miracle Fiber

For years, woolen mats have been soaking up oil spills. When the Exxon Valdez fouled Prince William Sound, for example, wool mats and mittens helped clean the shore and wipe down aquatic birds. “This is a product that’s already available,” says Bob Padula, an extension educator and sheep farmer from Chippewa County.

Padula and Bill Head, a sheep scientist at WCROC, speculated that woolen oil mats would work as horticultural mulch. “Everybody is always trying to duplicate wool’s qualities,” Head explains. But could this miracle fiber inhibit weeds, preserve soil moisture and protect young plants?

Experts from the University of Minnesota, the North Central Soil Conservation Research Lab, AURI and the North American Strawberry Growers Association (NASGA) are collaborating to find an answer. The research, which began in 1998, compares wool mulch mats with standard herbicides and traditional grass, wood chip and plastic mulches. The trials are being carried out on apple trees and strawberry plants — high-value specialty crops that require careful weed management.

In addition to weed control, the study is measuring wool’s effect on:

• nutrient transfer
• moisture retention
• soil temperature
• fruit production

Wool vs. Weeds

WCROC’s young apple orchard faces east, overlooking the Pomme de Terre River valley. Planted in May 1998, the slender Red Mac saplings are now between three and seven centimeters in circumference. The ground under the largest saplings is covered with low-value wool, fashioned into felt-like sheets about one-eighth inch thick.

Two years into the trials, the mulch is showing promise, says Steve Poppe, WCROC research plot coordinator. Though results are preliminary, trees mulched with wool are among the fastest growing in the plot, he says. Wood chip mulch is showing comparable results.

Experiments have demonstrated that fertilizer, water and herbicides penetrate wool mulch. Wool also inhibits weed growth. “We worked the soil before planting the trees,” Poppe says, “so we did have an initial flush of weeds that came through the wool. We applied one treatment of herbicide, and weeds did not re-emerge.”

In addition, Poppe says, soil probes have revealed that wool mulch moderates soil temperatures, insulating young trees from temperature fluctuations.

Healthy Plants

Encouraging results have also been observed in strawberries, Poppe says. In 1998, greenhouse trials showed that strawberry daughter plants would root through wool mulch. Field trials last year confirmed the finding.

“Wool created an environment that was great for producing daughter plants,” Poppe says. In the Morris research plots, “the wool mulch had the highest number of rooted daughter plants,” he says. “Plants appeared vigorous and healthy when compared to the standard herbicide treatment.”

Wool also controlled weeds in his strawberries, says Jacobson, who is running duplicate trials. “We didn’t have to apply any herbicide at all on the wool mulch,” he says. The mats also eliminated the need for hand hoeing. “The number of weeds was exactly zero where the mulch was.”

Weed control is the number one problem in establishing a stand of strawberry plants, Jacobson says. “There are so few herbicides registered for small fruits, so our options for weed control are really limited.”

Those options will soon shrink even more, says Poppe, a commercial strawberry producer for 15 years. “Strawberry growers have only four approved herbicides. And we expect to lose one or two of those in the coming years.” California and Florida growers are in a particularly tight bind, Poppe says. Fruit growers there rely on a chemical soil sterilizer that will be banned in 2005, “so they are really scrambling to find a substitute.”

This adds urgency to the wool mulch project, says Poppe, who is getting inquiries about the research from fruit growers and scientists around the country. “They see this as very important.”

Minnesota Grown Goal

Although Minnesota has a half dozen woolen mills, few if any use a substantial amount of locally-grown wool, Padula says. One reason is Minnesota wool is generally low quality. Minnesota’s sheep industry — which has emphasized meat rather than fiber — also lacks an efficient wool storage and distribution system, he says.

That infrastructure won’t develop in Minnesota without stronger demand for local wool, says Michael Sparby, manager of AURI’s Morris field office.

Wool mulch mats could provide a good market for Minnesota’s low-grade fiber, he says.

Currently, Minnesota does not have the manufacturing capability for wool mulch. Mats are made in Texas, adding substantial transportation cost. “Ideally,” Sparby says, “we would like to see Minnesota sheep producers get together to do the processing. That’s the goal — to have a Minnesota grown and manufactured product.”