IPM Pest Information Pages
Seedling Blights: Kentucky Soybean IPM
Seed and seedling diseases can cause seeds to rot prior to
germination or seedlings to rot and die
before they emerge from the soil. Emerged seedlings will
have varying degrees of root rot, lower
stem cankering and rot, seed leaf lesions, and stunting.
Plants may die or survive infection,
depending on the severity of disease and growing
Generally only scattered individual plants or small groups
of plants will be killed with seedling
Several fungi can cause seedling blight and the
symptoms observed may vary according
to the fungi involved. Infected seedlings may contain
small, black, dry sunken lesions on the
cotyledons. Infected stem tissues may be translucent to
brown or reddish in color. A soft, water
rot is often produced. Dry weather causes infected plants
to become dry and shredded.
Outermost tissues of large roots may slough off. Smaller
roots may be decayed and break away
from plants when pulled from the soil.
Seedling blight and seedling disease are caused by various
fungi. Depending on the fungus
involved, they can survive in the seed, soil and infested
Disease is usually promoted
by adverse growing conditions and stress during seed
germination and emergence. Low soil
temperatures from 50 to 60 degrees F and high soil moisture are
favorable to disease development. Low,
wet areas of fields are likely to show the first symptoms
of the disease.
Minimum tillage fields may
be more prone to disease as are seed of lower germination
and poor seed quality. Herbicide injury
or insect damage to young seedlings may also increase
seedling diseases, especially those caused
by Rhizoctonia and Pythium.
- Fields should be check every two weeks from planting until
- At each scouting
site, examine two rows of plants ten feet in length .
for dead or dying seedlings.
number of sites you will need to check in each field is
based on the field size. To determine the
number of scouting sites see the field size and number of
- At each site you will
need to note a rating of 0 to 3 based on the following
- 0 =no disease seedlings;
- 1 = up to one infected plant per two foot of row, a few
- 2 = between one and four infested plants per two foot of
row, several plants missing;
- 3 = more than four diseased plants per two foot of row,
many plants missing, obvious loss of yield
expected due to poor stand.
- Plant high-quality, disease-free seed or certified seed.
Rotate soybeans with other crops.
planting in cool, wet soils.
- Maintain balanced soil
- Improve surface drainage patterns,
where problems exist.
- Rotation of beans with other crops
may reduce levels of some fungi.
However, rotation will have little effect on fungi such as
Rhizoctonia, Pythium, Phytophthora and
- Seed and seedling diseases are generally
encouraged by reduced tillage systems.
References and Additional Information
- IPM-3 Kentucky IPM Manual for Soybeans
- PPA-10b Kentucky Plant Disease Management Guide for Soybean
by D.E. Hershman, Extension Plant Pathology, University of Kentucky
- Compendium of Soybean Diseases, J.B. Sinclair and P. A.
Backman (The American
Phytopathological Society Press)