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High Risk of Soybean Sudden Death Syndrome This Spring
With only 20% of the nation’s soybeans planted thus far (according to the USDA), and more rain on the way in key soybean-producing states, the risk for sudden death syndrome (SDS) in soybeans is unusually high.
SDS is caused by a fusarium pathogen in the soil, favoring the cool, wet conditions that have occurred this spring, says Jeremiah Mullock, insecticide/nematicide lead for seed treatments at BASF.
Soybean growers often think of SDS as a foliar disease later in the growing season.
“What’s often unrecognized is the root rot that occurs earlier in the season,” Mullock says.
Caused by a soilborne fungus, SDS can affect soybeans very early in the season, infecting roots sometimes as quickly as a few days after germination. The fungus produces toxins that plants transport up to their leaves, which results in foliar symptoms. Normally this occurs after flowering, but it can occur during early soybean growth stages on susceptible varieties or when conditions are cool and wet, according to the Crop Protection Network.
Since it’s so difficult to identify SDS in the early season, growers should scout their fields in SDS-prone fields. SDS symptoms have a blue color on the root system, combined with black fungal growth on the roots.
Later in the season, SDS symptoms move above ground, with inner vein necrosis that leads to chlorosis (or vice versa), Mullock adds. At first, affected fields will show yellow chlorotic spots between veins of the leaves. Then, spots become brown, and the pith of the stem of affected plants is white. The taproot of the soybean plant will show decay, with a cobalt-colored fungal growth on the root.
There’s nothing you can do once you see SDS in fields.
“Once you see those symptoms, it’s too late,” he explains. “Fusarium can affect within a few hours to days after planting.”
The only way to combat SDS is before it starts. Fields where SDS has occurred before should not be rotated into soybeans this year, as the disease risk is high, given cool, damp soils this spring.
Other management considerations come from the Soybean Research and Information Initiative:
If you must plant in fields that have exhibited SDS in the past, use tolerant varieties. These are harder to find in early maturity groups. Several universities conduct extensive testing of varietal reaction to SDS. Select varieties with solid agronomics. In many areas, resistance to both SDS and SCN is needed.
Plant early, but in warm, dry soil. The pathogen prefers cool, wet soil for infection. Move planting dates a week or two after regular early planting dates or till to promote earlier warming of soils. This is easier to do in southern areas of the region than the northern ones, where yield potential may be lost the later a field is planted. NCSRP researchers recommend planting early as long as an SDS-tolerant variety is planted, but do not plant a susceptible variety in a field with a history of SDS. If you have a field with a history of SDS, try to plant it later than other fields.
Use high-quality seed. Quality seed has more vigor and germinates and emerges more quickly. Maintain crop fertility based on soil tests.
Fungicides. BASF’s iLevo is the only commercial seed-applied fungicide that protects against SDS. In fields where SDS is present, iLevo provides a 4- to 10-bushel-per-acre yield increase over unprotected seed. Foliar fungicides are not effective against SDS as the fungus remains in the root system.
Crop rotation. Since SDS can overwinter in the soil and crop residue, rotating from consecutive years of soybeans is wise. Although, Mullock says, SDS can overwinter in a variety of weed species, including lambsquarters, pigweeds, and others.