Leopold Center for Sustainable Agriculture

Finding sustainable weed control for Iowa vineyards

Back to Leopold Letter Fall 2009

By ALLISON SEVERSON, Communications Assistant

Not only do Iowa vineyards produce great wine, but in the future, Iowa-grown grapes may be among the most sustainably grown in the country. The question is: how can Iowa grape growers reduce their chemical use and control weeds while still producing top yields and high-quality fruit? Iowa State University horticulture professor Gail Nonnecke is researching sustainable solutions to this problem.

The latest grape-growing project funded by the Leopold Center and led by Nonnecke looks at weed control alternatives to herbicides and pesticides in Iowa vineyards.

“It’s an exciting time in Iowa, the grape industry is growing, there are so many new growers and new vineyards, and also many educational opportunities for grape growers in Iowa,” she said.

Nonnecke noted that many vineyards are already using some sustainable practices, such as growing perennial grasses between the rows. “Often though, the missing link is the three-foot-wide bare strip of exposed soil under the trellis row,” she said.

“Quality is always important, but it is critical in producing grapes since the fruit quality affects the quality of the wine,” Nonnecke explained. “To produce excellent grapes, controlling weeds while keeping yields and fruit quality high is vital, and finding a way to do this that also keeps the soil healthy and productive is central to our project.”

To find a way to effectively control weeds while not leaving soil exposed, Nonnecke and Lisa Wasko, graduate student in horticulture and soil science, are comparing four weed control methods: herbicides, cultivation, mulch and living mulch.

The conventional herbicide and cultivation treatments leave the ground bare, exposing soil to erosion and possibly compromising its productivity. The cultivation method also seems to decrease yield more than other methods of weed control.

Straw mulch is effective and often used in organic vineyards. The straw controls the weeds, but also retains more moisture than other methods and can lead to constant wet roots and problems for the vines.

For the living mulch treatment, Nonnecke planted creeping red fescue (Festuca rubra), which prevents weeds from appearing and grows around grape vines to serve as a ground cover. Creeping red fescue is dense, which blocks the weeds and preserves the biological attributes of the soil.

Nonnecke’s viticulture research began at Pennsylvania State University, where she earned her bachelor’s and master’s degrees, and at Ohio State, where she received a Ph.D. “I grew up on a farm with a large diversity of crops, and I’ve been interested in viticulture for some time,” she said. “It’s exciting that Iowa is starting to see more vineyards and grape growers.”

“We need a weed management system that maintains soil quality, provides excellent growth and development and provides high fruit quality. If we can have this practice and provide it to Iowa grape growers, that would be an excellent addition,” she added. “By using practices that enhance soil quality of the vineyard, we can increase the sustainability of the vineyard in the long-term.”

New designation to help Iowa grape growers

A Leopold Center-funded project several years ago may pay big future dividends to Iowa grape growers. Work on that project was instrumental in establishment of the first American Viticultural Area (or AVA) in Iowa, recently approved by federal regulators.

The new region, the Upper Mississippi River Valley AVA, includes 18 counties in northeast Iowa and is the largest in the United States. A two-year Leopold Center grant helped Limestone Bluffs RC&D in Maquoketa start the application process in 2005. The result was the valued AVA designation that recognizes unique grape-growing regions and opens new markets for quality Iowa wine.

Since 2001, the Leopold Center has invested $238,000 in research and development of the Iowa grape and wine industries. The investment includes support of producer workshops and the Midwest Grape and Wine Industry Institute at ISU, and five competitive grants for research on vineyard management, economic feasibility, alternatives to pesticide use, and resources for people interested in starting a vineyard or winery.

In 2000, the Center issued a widely-cited “Grape Expectations” report about historical grape production and potential for redevelopment of the industry in Iowa.

Back to Leopold Letter Fall 2009