Soybean diseases to watch for

Soybean diseases that max out in a cool, wet year thrived in 2009. Even farmers with 30-inch soybean rows battled white mold, and that’s not supposed to happen. However, the disease challenges you face in soybeans in 2010 could be different.

The Indiana Certified Crop Advisers panel explains how to prepare for 2010. The panel includes Greg Kneubuhler, G & K Concepts Inc., Harlan; Jeff Nagel with Ceres Solutions, Lafayette; and Darrell Shemwell, branch manager for the Poseyville branch of the Posey County Co-op.

Which soybean diseases overwinter here? Which ones are always a threat? Would a cold winter reduce severity of diseases?

KNEUBUHLER: Most soybean diseases either overwinter in soybean residue or soil. A comprehensive and integrated disease management program should include use of adapted, disease-resistant varieties (when available), high-quality, disease-free seed, a well-drained, fertile seedbed and crop rotations. It should also include balanced soil fertility and proper soil reaction (pH), plus control of fungi, insects and weeds. Cold winters typically don’t reduce severity of diseases.

NAGEL: Whether a disease develops in any given year is based on growing a susceptible crop, having the pathogen present in the field, and getting the right environmental conditions.

Seed and seedling blights that overwinter in residue and/or soil include phytophthora, pythium, fusarium and rhizoctonia. Fungicide seed treatments help protect the seed and the early seedling stage, allowing better stand establishment.

Select varieties with Rps resistance genes and high field tolerance if phytophthora is a concern. To reduce the impact of sudden death syndrome, select varieties with good SDS tolerance coupled with soybean cyst nematode resistance.

White mold is managed by variety selection, seeding rates and row spacing. Apply foliar fungicides at flowering if necessary.

SHEMWELL: The problem with diseases like white mold and brown stem rot is that what causes them can exist in the soil for several years. White mold is also called sclerotinia stem rot. It produces bodies called sclerotia that can survive as long as seven years. The organism that causes brown stem rot can last as long as three to five years.

2009 an unusual year for diseases hitting soybeans

Sudden death syndrome was first detected in Indiana in southwestern counties more than 20 years ago. However, Chuck Mansfield says that while he saw a few fields hit hard by SDS last year, the disease probably didn’t cause significant damage in most southwestern Indiana fields.

Mansfield is a Purdue University Extension agronomist based at Vincennes. “The disease came in rather late,” he says. “That probably helped.”

The same wasn’t true everywhere. A Morgan County farmer saw SDS come in so early that seed reps questioned if it was SDS — until they saw it. What stood out on this farm, he notes, was wide variation in how varieties withstood SDS pressure.

Mansfield saw tons of aphids in September, an extremely unusual sighting in southwest Indiana. And he also saw a fair amount of purple seed stain, a longtime minor disease that tends to hang around. “It’s a seed-borne disease,” he notes. Since it also survives in residue, it can reappear year after year.

This article published in the January, 2010 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.