Sudden Death Syndrome

July 30, 1999
Several individuals have reported Sudden Death Syndrome (SDS) on soybeans (this is unconfirmed). Plants infected with SDS have reduced yield due to premature plant death, pod abortion, lack of pod fill, and low test weight. Growers need to be aware of the environmental conditions that favor SDS development, the symptomology that can help in diagnosis, and how to lessen the impact of SDS.

SDS is caused by the soilborne fungus Fusarium solani and generally appears about midsummer, usually after blooming. The disease is favored by cool temperatures and by relatively high soil moisture levels through the first half of the growing season. The initial symptom of SDS is the appearance of small, yellow spots, usually on the upper leaves. These spots enlarge and the tissues turn brown between the veins; however, the venial tissues remain green. Leaflets may drop prematurely, leaving the petioles attached. Flowers may abort, and pods usually do not fill. The first pod sets may have a few beans in them, which remain small. Later pods may not fill or may have immature green seed. Another characteristic of SDS is that the interior of the stem (pith region) remains white. If the pith is discolored, it may indicate the presence of another disease, brown stem rot.

No direct control methods have been identified for SDS. No fungicide or nematicide will adequately reduce SDS levels in a field. Tillage does not appear to directly impact the disease, although environmental conditions favoring wet or cool soils may increase chances of infections. However, the following can be beneficial in lessening the impact of SDS:

· Select varieties that show more tolerance or resistance to SDS. Southern Illinois University researchers have been evaluating soybean varieties for many years and can provide information on the performance of these varieties under conditions where SDS is a problem. For more information, contact the Department of Plant Soil Sciences and Research Studies at SIU.

· Select varieties of soybeans that will mature at different times. Use either different maturities within a maturity group or use different maturity groups. Early-maturing or early-planted soybeans appear to be more susceptible. Extend planting times so that allbeans are not at the same growth stage at the same time. However, do notwait past the suggested time for your area.

· Grow well-adapted, high-yielding varieties in a warm, well-drained, fertile soil. Reduction of soil compaction will help drainage and also improve root growth and development, two factors that can affect SDS development.

· Control other diseases, weeds, and insects that can stress or weaken a plant. This may help plants tolerate SDS. Control and monitor soybean cyst nematode (SCN) populations. Although not directly involved in SDS, SCN populations over the suggested threshold will affect plant growth and development.

· Crop rotation, although not consistent in greatly reducing levels of the Fusarium fungus, is definitely beneficial in reducing the buildup of other pathogens (such as SCN) that may weaken the plant.

· Although SDS is not seed transmitted, seeds from infected plants are small in size and tend to produce weaker seedlings than those from healthy plants. Therefore, do not save seed from SDS-infected areas.--Joe Toman

Author: Joe Toman