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July 24, 2003

Agronomist: Weather deals Indiana soybeans near knockout blow

WEST LAFAYETTE, Ind. – Indiana soybeans have suffered a beating at the hands of Mother Nature this spring and summer. It's no wonder, then, that the crop looks down for the count, said Ellsworth Christmas, Purdue University Cooperative Extension Service soybean specialist.

Many soybean fields in central and northern Indiana that weren't washed away by floods are stunted and pale from multiple storms, standing water and fluctuating temperatures, Christmas said. In southern Indiana, excessive spring precipitation pushed back soybean planting, reducing yield potential, he said.

"Right now the big concerns are related to the color of the crop and the fact that it is not growing," Christmas said. "That's all related directly to waterlogged or saturated soils. Any time you have saturated soils the nodules are not producing adequate nitrogen for the plant.

"Couple this with the fact that we've had overcast days, and the plants were not producing a lot of photosynthates to send down to that root system to support the roots, as well as the nodules. However, should the soils dry out and the nodules become either more active or re-established, then we'll see the plants start to darken in color and look quite normal."

For the moment, the crop continues to decline. As of Sunday (7/20), 49 percent of Hoosier soybean acres were rated "good" or "excellent," down 2 percent from one week earlier and off 8 percent since July 6, according to the Purdue-based Indiana Agricultural Statistics Service (IASS). The IASS rated 19 percent of acres "poor" or "very poor" on July 20, up 8 percent in two weeks.

Plant development also has slipped, the IASS reported. Thirty-six percent of the soybean acreage was blooming by July 20, up 1 percent from the same period in 2002, but well off the five-year average of 63 percent. Only 5 percent of soybean acres were setting pods by Sunday, compared with 18 percent for the five-year average.

Indiana farmers planted about 5.4 million acres of soybeans this year, down 7 percent from 2002.

Christmas said soilborne diseases could further damage an already fragile crop. Soybean fields in northern Indiana are especially vulnerable, he said.

"A couple of things we need to be on the lookout for are diseases that can be triggered by these weather conditions," he said. "One of those is Sudden Death Syndrome, particularly if those plants were under a lot of stress early and infection occurred. If we get rainy conditions or saturated soils during early pod development, it could trigger the toxic phase of Sudden Death Syndrome.

"The other disease, which most likely will be in northern Indiana, is Sclerotinia, or what we call white mold. Again, we have wet conditions, high humidity in the canopy, relatively cool nighttime temperatures and flowers on the plant. This all is very conducive to white mold infection."

Sudden Death Syndrome (SDS) can ruin a soybean crop. The SDS fungus, which favors wet field conditions, produces small, yellow blotches on soybean leaves. The plant tissue within the infected area becomes brown and dies, impairing the plant's grain-making ability.

White mold attacks the soybean plant's stem, covering it with a light-colored, fluffy growth. These lesions cause premature plant death.

Farmers in southern Indiana counties struggled to get soybeans planted by May 20, the ending date for maximum yield potential. Most soybean acres in the region were seeded around mid-June or later, Christmas said.

"Yield potential on late-planted beans is going to be lower. We'll see that happen this year in the southern third of the state," he said. "The one good thing about it is we'll probably see a lower incidence of Sudden Death Syndrome in southern Indiana than we normally see."

Root rot diseases are surprisingly absent from the late-planted crop, Christmas said.

"Let's hope that we have good growing conditions the remainder of the season and get adequate moisture during August and early September to fill the pods on the late-planted beans in southern Indiana," he said.

At this point, farmers can do little to improve their soybean crops other than control weeds, Christmas said. He advised against applying nitrogen – even to plants starved for the nutrient.

"It's a waste of money because the plants prefer the nitrogen when it's applied either as a fertilizer or when it's available in the soil as organic material that breaks down," he said. "If you apply nitrogen you can make the plant look better, but it's not going to do you any good in terms of yield."

Writer: Steve Leer, (765) 494-8415, sleer@purdue.edu

Source: Ellsworth Christmas, (765) 494-6373, echristmas@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

Related Web site:
Purdue University Department of Agronomy


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