Plant Disease: Purple Seed Stain

Taxonomy:

Distribution:

• World Wide

Symptoms:

• The most common symptom of this disease occurs on the seed.


• Infected seeds may appear healthy or have pink to purple spots that range in size from specks to large blotches that cover the entire surface.


• The discoloration extends from the seed hilum.


• Yield is not affected by the seed phase of the disease but the value of crop is lessened when it is downgraded due to the color variation.


• Seeds with a very high percentage of discoloration have lower oil content and higher protein content compared to healthy seed.


• Germination and seedling emergence is lower from purple seed stain infected seeds than from those that are healthy.


• Cotyledons of infected seedlings shrivel, turn purple and drop.


• Mildly infected seedlings survive but produce stunted plants.


• The leaf blight phase may be evident at the beginning of seed set.


• Young leaves on the upper portion of the plant are affected and have a dark reddish purple bronzing.

Seed infected with purple seed stain

• Leaves will have irregular shaped reddish purple lesions that vary in size from small specks to spots that are 1 cm in diameter.


• Lesions occur on both upper and lower leaf surfaces. Large necrotic patches form when the lesions coalesce and veinal necrosis may also be evident.


• Severely affected upper leaves are often shed with the petioles being held on the plant and the lower leaves remain attached.


• Infection sites on petioles and stems are sunken red lesions that are several mm in length characterize stems.

Bronzing of leaves cause by Cercospora

Management:

• Soybean cultivars vary in their susceptibility to seed and/or leaf phases of the disease.


• Seed lots with a high percentage of infected seed should be treated with a seed treatment fungicide.


• Foliar fungicides may be applied to prevent pod infection and subsequent seed contamination, but is not economically feasible in Nebraska.


• Crop Rotation and residue in corporation will reduce inoculum by breaking down infested residue.