Kansas is expected to produce a record-large soybean crop this year, but a Kansas State University scientist said the state's soybeans have been hit by the highest levels on record of sudden death syndrome (SDS), a soil-borne fungal disease.

"So far, the known cases have been in the eastern two-thirds of the state," said Doug Jardine, state leader in plant pathology with K- State Research and Extension.

The U.S. Department of Agriculture on Sept. 10 forecast Kansas soybean production at 94.4 million bushels, 65 percent more than last year's drought-stricken crop and a record for the state. Acreage for harvest was expected to total 2.55 million acres, unchanged from USDA's Aug. 1 forecast, but up 3 percent from a year earlier. Yields estimates were an average 37 bushels per acre, up 3 bushels from Aug. 1's forecast and 14 bushels above 2003's. If realized, that would equal the record-high yields of 1992, 1996, and 1997.

In Kansas, SDS is nearly always found in irrigated soybeans and is slightly worse in flooded fields than in pivot-irrigated fields, Jardine explained. It seems to appear in the best-managed fields, hence its association in Kansas with irrigation.

"I have found it in some very deep, non-irrigated river-bottom fields along the Missouri River, as well," he said.

Infection actually takes place much earlier in the year, when soils are cool and wet. Symptoms do not develop, however, until the stress of pod filling begins – typically in late summer.

Infected leaves develop small cream-colored spots. Over several days, the spots begin to coalesce and turn brown. After a week or so, the entire leaf is brown, except for its veins. The leaf blades eventually drop, but the petiole remains attached to the stem, he said.

"If the plants are dug up and the tap root is split open, there is usually a distinct brown to gray discoloration of the inner root tissues," Jardine added.

Symptoms usually appear in the wettest areas of a field. It is rare for entire fields to be affected. Thus, direct yield loss is determined by the actual area of a field that's infected and by the stage of pod development at which symptoms begin to appear.

"Even the worst-affected fields I have seen this year should have less than a 20 percent yield loss," Jardine said.

In Kansas, SDS is highly associated with infestations of soybean cyst nematode (SCN), however. Most fields that have SDS test positive for SCN, the plant pathologist said. Those that do not are probably infested, but have yet to reach the level of detection.

Jardine said that control measures start with planting SDS-tolerant varieties. In addition, delaying planting until the end of the normal soybean planting period helps by allowing soils to warm up and dry out somewhat.

"Research in Illinois, where SDS is an even bigger problem, indicates there also is a strong correlation between SDS and soil compaction. For that reason, deep tillage to eliminate compaction can reduce SDS severity," he said. "Working to reduce the levels of SCN in a field will also help to some extent."


K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus in Manhattan.