For the fourth straight year, Wisconsin will lead the nation with a cranberry harvest forecast at 2.4 million barrels of the tart, native fruit. From Tomah to Manitowish Waters the colorful harvest means income and jobs. Cranberries are the state”s most valuable fruit crop, with the 1997 crop valued at $162 million.
Once a relish served during fall and winter holidays, cranberries are now an important part of juice blends enjoyed year-round. Wisconsin growers have captured a good bit of that expanding market. Today they are using the latest research and technology to produce the crop while minimizing harm to the environment.
Most cranberries are grown near wetlands where pesticides can threaten fish and wildlife. Yet unless growers control pests, they can reduce cranberry yields by as much as 80 percent.
Concern about chemicals prompted more than a decade of research by University of Wisconsin-Madison scientists. “We”ve found new ways and new tools to control pests,” says Dan Mahr, a professor and extension specialist in the Department of Entomology in the College of Agricultural and Life Sciences.
Mahr and co-workers in the Departments of Horticulture and Plant Pathology have produced a computer program that gives growers rapid access to all the latest information on managing the crop. The Wisconsin research incorporated in the program helps growers manage pests with far fewer chemicals than they once used.
“I can foresee a day when cranberry growers control virtually all insect pests with 10 percent to 25 percent of the insecticide used historically,” says Mahr, who works with fruit growers across the state. “Even this small amount will only be used in certain years when other methods have failed.”
With the program – called Cranberry Crop Manager or CCM for short – growers enter and track records on weather, pest monitoring and pest control applications. When they encounter pests, growers can check a CCM section that holds an encyclopedia of information about cranberry pests, including photos and recommendations for controlling 70 weeds, 12 insects, and five diseases.
CCM”s predictive features raise it above other management tools. CCM tells growers when to look for problems and presents alternative control measures for the crop”s most serious pests.
“CCM lets growers anticipate events and plan a program that integrates decisions,” says horticulturist Teryl Roper. “It brings together the research and tells growers the positive and negative consequences of decisions they are considering.”
The program marks a dramatic step forward. For decades, little was known about cranberry pests except what chemicals would kill them. Growers applied pesticides at set calendar intervals.
Then in 1986 the College and the Cooperate Extension Service launched a five-year effort to develop an integrated pest management (IPM) program for cranberries. The IPM program emphasized checking for pests – called monitoring or scouting – and applying pesticides only when pest populations were likely to damage the crop.
“That was the first time growers made pest-management decisions based on what was out there, rather than how long it had been since they last sprayed,” Mahr says. “Growers who had been making several applications a year to control a single insect pest found that they could skip one or maybe two of those sprays in some years.” Today, Mahr estimates that 80 to 85 percent of Wisconsin”s cranberry acreage is under IPM.
“Cranberry growers were faced with a complex of pests that they were using chemicals to control,” Mahr says. “Largely because growers were motivated, they”ve adopted new practices that reduced pesticide applications.”
With support from cranberry processor Ocean Spray, the researchers next explored other ways to advance cranberry IPM.
“We decided that growers needed tools that would tell them when to monitor for pests and what pests to look for,” says Mahr, who wanted to develop non-chemical alternatives based on biological information about pests.
Mahr spent an additional five years studying Wisconsin”s most destructive cranberry pest, the blackheaded fireworm. He and Stephen Cockfield, a postdoctoral scientist, discovered how to predict when the timing of the insect stage made it most susceptible to control. The researchers found that fireworms may starve if they hatch before the cranberry buds begin growing in spring. In other years, growers may be able to control them by flooding the beds briefly. If growers must spray, Mahr says, they can use a natural insecticide from bacteria.
The researchers continue work to improve growers” options. Fruit pathologist Patricia McManus is focusing on cottonball, Wisconsin”s most important cranberry disease. “It”s a fungal disease that can destroy up to one-third of the berries on some marshes,” McManus says.
McManus is looking for alternative ways of controlling the disease with fewer fungicide applications. She”s testing different cranberry varieties to see if any might resist the disease naturally, and studying how spreading sand over cranberry beds affects the disease. One of her students has identified bacteria from cranberry flowers that inhibit the cottonball fungus in the laboratory. Such bacteria might one day replace chemicals in controlling cottonball.
Mahr and entomologist Kathleen Chapman are now studying cranberry tipworm, a pest whose feeding causes cranberry vines to produce vegetative shoots rather than those yielding fruit. Growers haven”t been able to monitor the tiny midges. The researchers are identifying compounds that attract the insects so growers could put out baited traps and gauge tipworm populations.