Callaway County
Callaway County
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Jarman's Weekly Agronomy News August 23, 2000 |
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Sudden Death Syndrome of Soybeans |
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Sudden death syndrome (SDS) is beginning to show up on soybeans in Callaway County. In years when conditions are favorable for infection and symptom development, SDS may be found in most areas of the state. Symptoms may occur at any time from late bloom through pod fill, but most commonly occur from pod set to early pod fill. The time of symptom development appears to be related to weather conditions, variety, date of planting, maturity group of the variety and general plant growth conditions. A fungus, Fusarium solani f. sp. glycines, evidently enters the roots early in the season but does little damage until the conditions are just right. Foliage symptoms begin as small yellow blotches in the interveinal leaf tissue which increase in size and merge to affect larger areas of leaf tissue. Veins typically stay green. The bright yellow blotches between the green veins give affected leaves a very striking appearance. Then yellow leaf tissue begins to turn brown. The top leaves are generally affected first. As the disease progresses, symptoms may develop over the entire plant and defoliation may occur. Severely affected leaflets may drop off the plant with the petioles remaining attached to the plant. SDS also causes a discoloration of root and lower stem that occurs when leaves are yellowing. When stems of affected plants are split from the root upward the root and lower stems are discolored from a milky tan to gray to reddish brown or brown color. The pith tissues remain white to light cream color. The plants may have smaller root systems than healthy plants. Roots on severely infected plants may be decayed and deteriorated making it easy to pull the plants from the ground. Affected plants may occur in somewhat circular to oval patches in a field. The patches may vary in size from several feet in diameter to areas of more than an acre in size. The number of patches per field is highly variable but there are usually several patches of affected plants scattered through a field. The patches may occur in irregularly shaped bands or pockets throughout the field. In severe cases a majority of the field may show symptoms. SDS has been associated with "maximum yield potential" soybean production, i.e., fields with optimum fertility, lime application and irrigation, and is more prevalent during cool, wet seasons. Field observations suggest that sudden death syndrome is more likely to occur and to be more severe with high soil moisture, whether supplied by rainfall or irrigation. High soil moisture during vegetative growth stages seems to be the most conducive to disease development. Also, the onset of SDS symptoms frequently is associated with wet conditions and below normal temperatures at or near bloom. There also appears to be a relationship between sudden death syndrome and soybean cyst nematode (SCN). Fields with sudden death syndrome frequently also have histories of (SCN). Not all of the contributing factors have to be present for a field to get SDS but yield losses due to sudden death syndrome range from trace losses to losses as high as 80 percent depending on variety and when the symptoms first appear. Although, losses in the range of 5 to 15 percent are more common. SDS at early pod fill is much more damaging than its appearance later in the season. Yield reduction is primarily from pod abortion, lack of pod fill, and low seed test weight. Management options for sudden death syndrome are somewhat limited but should include the following:
Other diseases may be present in area soybean fields due to rains during July and August. Wet leaves and warm or cool temperatures can stimulate leaf, stem, and pod diseases. Have these diseases identified to aid making management decision for the next season. Information for this article is from Laura Sweets, Extension Assistant Professor, MU CAFNR Plant Pathology, 573-884-7307.
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Plant
varieties which have performed well where sudden death syndrome has been
a problem.
