Soybean Rust or No, Don't Alter Management Practices

February 11, 2005

COLUMBUS, Ohio — The goal of any crop management is to utilize a production system that generates the most yields. Soybean growers should stick to that practice, even with the potential arrival of soybean rust looming large.

Growers, anticipating the presence of the aggressive fungus, may be considering making management changes to their crop in an attempt to find the most effective means of controlling it. But the move could be more harmful than helpful, said Jim Beuerlein, an Ohio State University Extension agronomist.

"There is no way to control this disease with just cultural practices alone. Growers should just keep doing what they've always done in growing soybeans," said Beuerlein. "We don't want growers to make production changes. That's just bad economics."

Many factors are taken into consideration when dealing with cultural practices, including variety resistance, variety maturity, seeding rates, planting dates, row spacing and plant health. While some may make a slight difference, most won't be effective at all.

Choosing a resistant variety is impossible at the moment, because it is not known if any exist that protect against soybean rust. Short season varieties may help reduce yield losses associated with the disease because the plants could mature earlier than the disease's arrival. However, little seed is available for these varieties for growers to use.

Planting earlier may be effective, but, in reality, may not make a large enough difference in escaping large yield losses. "Growers would probably only be changing the maturity day by about a week. It'll help a little bit, but it may not be near enough," said Beuerlein. "And, of course, all of this is always dependent on the weather."

Two big practices that Beuerlein is encouraging growers not to alter are seeding rates and row spacing of the crop. Research from the University of Wisconsin on sclerotinia white mold — a disease with similar characteristics to soybean rust — has shown that reducing seeding rates and row spacing causes more yield loss than what it makes up for in reducing the severity of the disease.

"It is believed that the spread of soybean rust is linked to humidity in the canopy, so growers feel that they can help reduce the disease by widening their rows and/or reducing seeding rates," said Beuerlein. "In actuality, a grower is better off sticking to the current practice of 7.5-inch rows and 200,000 seeds per acre, than making any changes."

Beuerlein said that increasing row spacing from 7.5 inches to 30 inches will result in a yield loss of five to seven bushels per acre. Reducing the seeding rates from 200,000 to 120,000 seeds per acre could cause as much as 10 percent yield losses in fields where soybeans don't get 30 inches tall.

"We know that we have fungicides that can control this disease, so growers should be educating themselves on the types of fungicides that are available for use in Ohio," said Beuerlein. "And a production practice that aids in effectively spraying is skip row."

Skip row production allows a grower to apply pesticides without causing damage to the crop.

"It makes spraying easier and there are no skips, no overlaps, no wasted chemicals and no missed spots," said Beuerlein. "And the yield loss associated with skip row is so minuscule it's not even noticeable. Growers are encouraged to practice skip row production, especially if they are going to have to deal with both rust and soybean aphids come August."

For more information on crop production and management related to soybean rust, log on to http://www.agcrops.osu.edu.

Author(s): 
Candace Pollock
Source(s): 
Jim Beuerlein