Some farmers are bucking the rotation reasoning and swapping out of soybeans. Costs are one factor. Disease is another. The decision, however, requires serious research.

Although many Midwest growers see the Freedom to Farm Act as a liberation from the corn-after-corn monoculture imposed by base acreage programs, some are bucking the trend toward increased soybean planting, planning to return a substantial amount of their acreage to continuous corn. They cite rising disease pressure in soybeans, a reassessment of farm profitability and the increased incidence of adult corn rootworms laying eggs in soybean fields as reasons to focus on doing what they feel they do best: growing corn.

"It was referred to as a Corn Belt for a reason," says Frank Shafer, of Wyoming, IL, who farms 4,800 acres with his family. Although the family had committed 43% of its acreage to soybeans last year, Shafer says, "We'd like to get back to two-thirds corn."

Diseases are "murdering us." Shafer says that escalating disease pressure in soybeans is a prime drain on yields and profits. His crop consultant, Dave Mowers of Mowers Soil Testing Plus in Toulon, IL, sums it up: "Soybean yields are faltering. Soybean cyst nematode is just murdering us in east-central Illinois. And we're starting to hear a lot about white mold. We have pools of disease spores building up in these soils when we allow only one year between crops."

The abundance of soybeans after last year's spring rains didn't help. Mike Corbin of New Ag Center in Monee, IL, points out that many fields in his area were planted last year to soybeans for the second or third year in a row - an invitation to disease problems.

Longer rotations will help reduce disease problems, Mowers says. "By leaving more time between soybean crops, we increase yield because it controls diseases and soybean cyst nematodes." Mowers recommends at least two years of corn between soybean crops. He suggests switching between SCN-resistant soybean varieties and conventional ones to balance between disease tolerance and prime genetics.

Account for fertility. When calculating the profitability of corn vs. soybeans, many farmers wrongly identify an every-other-year fertilizer application as an input for corn only. "Don't attribute the whole cost of fertilizer to corn when a portion of it should carry over to the beans," Mowers cautions. "With soybean fertility, just the P and K requirements are $20 to $30 per year. Plus the lime requirements, and they need a higher pH. That can be nearly $10 a year for the cost of keeping the pH up." Add it up and you may paint yourself a different profit picture.

Corn rootworm invading first-year corn. A prime reason for rotating between corn and soybeans - cultural control of corn rootworm - is losing its effectiveness in parts of the Corn Belt. Some Western corn rootworms seem to have lost their natural preference for laying eggs only in cornfields, explains Larry Bledsoe, extension entomologist at Purdue University.

Adult Western corn rootworm beetles are laying eggs in soybean, alfalfa and oat fields, among other places, in a wide swath of territory extending from central Illinois to western Ohio, says Bledsoe. The number of affected counties in Indiana jumped from 16 in 1996 to around 50 last year, he says.

In fact, for corn rootworm beetles willing to lay eggs outside of standing corn, drilled soybeans offer a great environment, Bledsoe notes. The soybean canopy keeps the soil cool and moist, and cornstalks from previous crops remain on the soil surface.

The bottom line: An increasing number of Midwest growers are finding themselves fighting corn rootworm in first-year corn.

Targeting adults, larvae. Mowers calls corn rootworm the single biggest yield limiter in corn and goes for control with both barrels. He recommends that a soil insecticide be applied on fields coming out of soybeans into corn, if rootworms have been a problem in first-year corn. In many continuous corn situations, he promotes an adult corn rootworm spray program: one or two over-the-top organophosphate or pyrethroid applications aimed at controlling pregnant females before they lay their eggs. Spraying for adult rootworm beetles can also reduce second-generation European corn borer populations when the timing is right, he adds.

Adult spray programs require careful scouting and precise timing. They can fit well where growers know they will be planting continuous corn and are committed to the program. On rented ground or fields where cropping decisions are being made year to year, they can present more of a financial gamble. "You have to decide by July 10 or July 15 in '97 where you're going to be in '98," says Shafer. "Some years, something comes up in the fall and we put in soybeans anyway."

Especially on prime corn-on-corn ground, Shafer hedges his bets with adult and larvae control. "Particularly in the bottoms, we do feel that it pays to control adult beetles and run a granular insecticide program anyway," he says. "Plus there's the minor pests - cutworm, wireworm, seedcorn beetle. In continuous corn situations, I think we have enough of those minor insect problems that, year in and year out, it pays to use a granular insecticide." Shafer chooses Force insecticide for his granular program in both first-year and continuous corn, citing the product's broad spectrum effectiveness.

Beans remain risk managers. Despite his shift to more continuous corn, Shafer hasn't soured on soybeans. As long as prices and weather fluctuate, growers will need to spread their risks. "I've seen years - fortunately, not many - when corn will make 90 bushels per acre and soybeans will make 55," he muses. "Beans are a much more stress-tolerant crop. it's risk management."

Not every midwestern farmer will opt out of rotation, notes Bledsoe. He points out that producers in the eastern Corn Belt, farther from the livestock markets, are likely to continue rotating most or all of their row crop acres. He says that - in spite of new rootworm problems - they still stand to gain improvements in soil tilth, a boost from nitrogen fixed by the beans, and a break in the weed and disease cycles that can affect corn. "I think this whole idea of continuous corn will probably not take hold quite as fast as you go further east," he says. "The majority will probably continue to rotate and just add the input cost of the rootworm control" on first-year corn in areas where the new behavioral pattern of Western corn rootworm is a problem.