Soybean Sudden Death Syndrome Update

Don Hershman, Extension Plant Pathologist

Symptoms of sudden death syndrome.

There have been numerous reports across the state of soybean sudden death syndrome (SDS) showing up in certain fields since August. SDS, which can be a devastating disease, is caused by the soil fungus Fusarium virguliforme (Fv).  Fv is actually a soilborne fungus that attacks roots early in the season and later causes a root rot. Infection is favored by cool soils with good moisture; thus, this spring was perfect for infection in most full-season fields. As plants go into the reproductive stages, the causal fungus produces a plant toxin that causes above ground foliar symptoms of yellowing and tissue death between the veins (see below picture), and later defoliation. If the disease comes into the field during the early pod development stages, and enough of the field is impacted, SDS can result in almost total yield loss. This is, however, an extremely rare event in KY. More typically, the disease causes significant yield losses in spots in a field - usually the lowest portions where soil moisture is greatest - but the majority of the field has little to know yield impact.  That is, most plants either escape disease altogether or symptoms come in after mid to late -pod fill. Plants showing late symptoms will generally yield very well. Thus, the appearance of symptoms is not necessarily a good indicator of yield loss potential. Timing of symptoms is everything when it comes to SDS.

Soybean Sudden Death Syndrome Showing Up

Don Hershman, Extension Plant Pathologist, University of Kentucky

Soybean sudden death syndrome (SDS) caused by the root-rotting, soil-borne fungus Fusarium virguliforme, is beginning to show up in soybean fields across the state. To my knowledge, all of the sightings are in patches of plants or individual plants, and are not field-wide. SDS has been seen in Kentucky each year, to one degree or another, since 1985.

SDS (Fig. 1) is evident first in foliage where plants show yellow blotches between the veins.

Fig 1. Range of SDS foliar symptoms.

Sometimes this this early symptom can look almost virus like. In most cases, blotches eventually coalesce and result in a yellow and brown discoloration between the veins, but the veins remain green. In severe cases, the leaflets will fall off, but the petioles will remain attached to the plant. Foliar symptoms are the result of a toxin produced by the fungus in diseased root tissue.