September 22, 2006

Sudden death syndrome strikes soy plants in US state of Iowa

Widespread infestation of sudden death syndrome (SDS) has been found in many soybean fields in eastern and central Iowa.

The disease was reported as early as July as cooler temperatures this summer may have contributed to its occurrence. In central Iowa, even though the incidence of infested fields is high, it is not as serious. In most instances, the disease occurs in small areas with limited yield damage.

The disease can cause premature defoliation in late summer. Some of the plants have been dying prematurely, a symptom which has not been seen previously. Plants with premature dying lack the typical drastic defoliation symptom of SDS, but diseased plants yellow and die gradually.

Symptoms typical of SDS plants include leaves with chlorotic spots and necrosis between green veins as well as deteriorating roots. Bluish fungal colonies may also form on the taproot in severe cases.

Brown stem rot (BSR) also causes premature defoliation and produces SDS-like foliar symptoms.

One simple way to separate the two diseases is that SDS causes root rot, and the pith of the infected soybean stem remains white. For BSR, the pith is brown and there is no root rot. Plants with SDS are easily pulled out because of root rot.

Soybean white mold is also present in eastern Iowa this year, returning after the 2004 outbreaks. However, the disease is less prevalent in central and western Iowa.