Leopold Center for Sustainable Agriculture

ISU professor tests new strategies to help Iowa apple growers

Back to Leopold Letter Summer 2008

By CAROL BROWN, Communications specialist

Iowa’s apple growers will have some additional tools in their orchard management kit, thanks to a research project funded by the Leopold Center's Ecology Initiative. Mark Gleason, a professor of plant pathology and horticulture, is leading the three-year study started in 2006 at the Iowa State University Horticulture Research Station north of Ames. He also has involved several Iowa commercial apple growers in the program.

Apple growers face challenges such as the decreasing effectiveness of conventional pest management programs for disease and insects, as well as government regulations on pesticides. They also are seeing shrinking profit margins for fresh-market apples. Gleason’s study, entitled New Strategies to Enhance Sustainability of Iowa Apple Orchards, explores pest management tactics including weed management, production standards for producing hard cider, and a grower-education program. He tested three new disease-resistant apple varieties—Redfree, Liberty and Gold Rush—that were planted at the research station in 2004.

Ground cover
To improve ground cover management, the study compared mulches against bare ground and grass. Grasses or bare ground are most common within apple orchards. But grass competes with the trees for water and nutrients, and bare ground fosters erosion.

Gleason used composted wood chip mulch, which he found to be beneficial for weed control and requiring fewer herbicide applications. The wood chips also held moisture in the soil and kept the temperature of the soil cooler than either grass or bare ground. Competition from grass for nutrients was virtually eliminated. The wood chips were placed in 2006 and reapplied this spring. As a bonus, the decomposing wood chips added organic matter, creating a healthier soil.

Pest control
When researching integrated pest management (IPM) systems, Gleason examined a disease-warning system for sooty blotch and flyspeck (SBFS) and new strategies for pesticides to control the codling moth. These problems are common for apple growers across the United States.

A disease-warning system is a weather-based tool in which the grower sprays only when weather conditions pose a significant risk of disease outbreak, as opposed to a regimented spraying schedule.

“The disease-warning system is an ecology-based pest management system,” said Gleason. “We found that the warning system works well, eliminating two to three fungicide sprays per season.”

The study also examined fungicide spray volume and tree pruning. Some commercial growers are experimenting with spraying more concentrated forms of fungicides, which has been shown to make a difference. Gleason noted that the reduction of spray volume and non-pruned trees can jeopardize the success of the disease-warning system.

“A modified strategy of IPM does a decent job and should take care of any pests,” said Gleason. “Note that we practiced a modification, not elimination, of fungicide application.”

Hard cider
ISU food science professors Cheryll Reitmeier and Lester Wilson oversee the hard cider portion of the study, aimed at helping Iowa apple growers explore the potential of hard cider as a value-added product.

Reitmeier and Wilson are testing different blends of apple varieties for hard cider production. A field day for the Iowa Fruit and Vegetable Growers Association was held at the Sutliff Winery in Lisbon, Iowa's only commercial manufacturer of hard cider. Attendees discussed fermentation and aging, carbonation and bottling for commercial hard cider.

They also are planning a one-day workshop on the ISU campus this fall. The workshop will review requirements to produce hard cider such as filtering, aging and bottling systems.

Gleason sees this research project as a holistic study, looking at all aspects of apple growth from soil health to high-quality fruit to marketable products. The Leopold Center grant has enabled him and his team to offer Iowa apple growers improved tools for orchard management, including new guidelines for spraying, applying mulch for ground cover, and the possibility of value-added products to their repertoire.

Back to Leopold Letter Summer 2008