By Dan Lemke

Just as every Napoleon has his Waterloo, most pests have natural enemies to keep them in check. Utilizing natural enemies and biological controls to combat pests can help producers reduce chemical treatments without sacrificing yields. They can also save money and the environment in the process.

Fruit cropping in Minnesota generates $10 million annually from more than 3,000 acres. PRO-funded research is generating new information on biological controls for fruit crop pests -- data specific to Minnesota's climate and varieties.

Apple mite fights

Tiny mites cause big headaches for Minnesota's apple growers. The chief villain is European red mite infestation, which results in small, discolored fruit.

Richard Gagné of the Minnesota Department of Agriculture is heading up PRO research into mite management in orchards. "We are trying to give growers options on mite control," he says. "We can reduce pesticide use by giving them some choices."

Gagné's research will help establish apple variety scales to show which trees are most susceptible to mites. Only half-way through the two-year research effort, it appears Haralson apple trees are most susceptible.

Another key objective of the mite research is to help growers determine economic thresholds -- the point where mite infestation is severe enough to warrant action. Projecting when treatment costs would exceed untreated crop losses helps producers avoid unnecessary spraying.

Gagné is also researching natural enemies which feed on the mites. Predatory insects such as Stethorus punctum, also called the "mite destroyer," and predatory mites can be effective in managing the pests.

European red mites overwinter as eggs, so many apple growers begin their annual treatments by spraying a thin film of oil on trees to suffocate the eggs. Miticides are sometimes mixed with the oil. Gagné's first year of research showed spraying one gallon of oil per acre yielded the same results as three or six gallons mixed with miticide.

The lower density of oil did not kill all the mites; instead, the survivors provided a vital food source for predators. "If the predatory mites have no food source, they starve and there is often a flare in populations of the harmful mites," Gagné says.

Gagné expects the information on variety scales and thresholds to be of value to orchards very soon, but knows natural enemy management to be the most difficult for producers to adopt.

Right now, Gagné says, much of the information producers use has been gathered from other states. "This research needs to be done almost on a per-state basis. Even in Michigan, which has almost the same temperatures as Minnesota, variables like moisture levels are different, so the results will be different."

Value-added IPM

Minnesota has about 125 apple orchards and 150 berry growing operations. A number of growers have implemented integrated pest management practices. IPM reduces the need for pesticides through crop rotation, scouting, weather monitoring, resistant crops, timing of planting and biological controls.

Previous AURI-funded research by the Minnesota Vegetable Growers Association has shown IPM can reduce pesticide use by 28 percent annually when compared to traditional calendar-based treatment programs. This saves apple growers $55 to $70 per acre and strawberry growers $25 to $35 per acre.

The challenge now lies not in proving IPM works, but in getting accurate information on prevailing diseases, pest levels and predisposing conditions out to producers in a timely manner.

"IPM is information intensive," says Kevin Edberg of the Minnesota Department of Agriculture. "But that information is only valuable if it's timely. So in this case, the delivery mechanism also adds value."

The Department's PRO project is developing a system for strawberry and apple growers to monitor key pests and diseases and promptly alert other growers to those conditions.

Another objective is to incorporate fruit crop pests into the Department's Plant Pest Survey. This will give growers access to information about what pests are showing up, in what numbers and where. This will aid grower awareness of what to scout for in their fields.

Key to it all is the quick dissemination of incoming information. Edberg hopes that using technology such as e-mail or fax will give producers more rapid access to breaking news.

"In addition to information about things like pest outbreaks, we want to use electronic communications to spread appropriate production or marketing information," Edberg says.

Ten apple orchards and 10 strawberry sites across the state will be monitored, with information made available to all Minnesota growers. So far, Edberg says about 50 fruit growers have signed up to get the IPM information, which will be updated weekly.

Strawberry fields take no cover

There may be as much value in proving what doesn't work as there is in finding what does. PRO research on cover crops in strawberries is a case in point.

In strawberries, only four herbicides are labeled as safe, so growers have few options for controlling weeds. Since cover crops suppress unwanted plant growth, U of M researcher Emily Hoover undertook a study of a recently developed cover crop, Brassica, for use in strawberries.

"The number of herbicides labeled for strawberries is decreasing and they aren't always effective," Hoover says. "Because there are fewer tools available, we need to find other options."

Hoover's experiments sought to find if the ground could be kept covered most of the growing season in a newly established strawberry planting without harming plant growth during the establishment year. The results showed it could not, because the competition was too intense.

In the first year of the study, strawberry plants in plots with Brassica flowered much later than those in control plots.

In the second year, the results were even more dramatic. Plants in plots using the cover crop yielded no fruit. While the cover crop did reduce erosion in strawberry test plots, because of the immense impact on yields, they are not a viable alternative during the establishment year.

"In strawberries, the establishment year is critical," Hoover says. "Until the plants are established, there is a lot of bare ground that needs to be covered.

"Using a living cover crop will be difficult, because the competition is just too intense."