Agricultural publication G04254---Reviewed March, 2009
Cotton Seedling Diseases:
James Allen Wrather,
University of Missouri Delta Center
Answers to Frequently Asked Questions
Gabe Sciumbato, Mississippi State, and
University of Tennessee
Q: What are cotton seedling diseases and what causes them?
A: Several different, normally harmless, microscopic organisms that
live on organic matter in the soil can attack cotton seedling roots in the
spring. These organisms are called fungi. The ones most commonly found
attacking cotton in Missouri are named Pythium, Fusarium, Rhizoctonia and
Thielaviopsis. A plant may be attacked by one of these or by several at the
same time. Each of these organisms causes a different disease, and the
symptoms are different for each. However, they are collectively
known as seedling diseases.
The organisms that cause seedling diseases are present in most soils. Once
established, they remain there indefinitely. They produce structures that
enable them to survive in the soil from year to year.
Seedling diseases become worse when the soil is cool and wet. These
conditions do not develop in Missouri every year. Because of yearly variations in weather, the
severity of cotton seedling diseases also varies. Cotton seedling diseases
cause more yield loss than any other disease in Missouri.
Q: How do cotton seedling diseases damage cotton?
A: The microscopic organisms that cause seedling diseases penetrate
and grow within the cotton root by secreting chemicals that
dissolve the root tissue. The organisms absorb the nutrients they
need for growth from the damaged root. The root damage
may vary from slight injury (which the root may outgrow), to
moderate injury (the plant lives but the root is permanently
damaged), to seedling death. Diseased roots are unable to absorb
water and nutrients as well as a healthy root, and the plant
will grow more slowly. Plants with permanently damaged roots usually shed
young bolls more quickly during
summer drought. They mature later, yield less and produce
poorer-quality lint than healthy plants.
Q: What are the symptoms of seedling diseases?
A: A healthy cotton seedling root is white and firm and the central root
(tap root) is long with numerous secondary, white roots emerging from the upper
taproot. A stand of healthy cotton seedlings is uniform with no skips.
Seedling diseases affect young plants in several ways. Dark, rotted areas (lesions)
develop on infected roots.
The tap root may be destroyed, leaving only shallow-growing lateral roots
to support the plant
Seedlings may wither and die after the
disease kills the root (
Figure 2). Plants that survive infection are often weak, more susceptible
to other diseases and
environmental stresses, and unproductive. Sometimes seedling diseases will
kill entire fields of young cotton. The most frequent result of this problem is
stands of weakened plants (Figure 3)
that grow slowly, yield poorly and have low-grade lint.
Figure 1. Shallow lateral roots left after the tap root has been destroyed by seedling disease.
Figure 2. Seedlings damaged or killed by seedling disease.
Figure 3. A thin, uneven cotton stand due to seedling disease.
Q: What can be done to prevent seedling diseases?
A: There is no way to eradicate the problem, but the following six steps
can be taken to minimize damage:
- Plant only when the soil temperature 4 inches deep has warmed up to about
65 degrees F by 8 am and plant only when five days of warm weather are predicted.
- Plant seeds that germinate quickly and produce vigorous seedlings.
There are two germination tests, a warm test and a cool test, that are
useful for predicting how a seed lot will perform in the field. In general,
the warm germ test (about 86 degrees F) will estimate the percent emergence
under highly favorable conditions, while the cool germ test (64 degrees F)
will estimate emergence under more typical, somewhat adverse conditions.
Minimum acceptable percent germination levels for cotton planting seed are
80 percent on the warm test and 50 percent on the cool test. The warm
germination test results are printed on most bags of seed. Growers should
ask their seed dealer for the warm and cool germ test results for their
planting seed, and should only plant seed that germinates well, especially
when planting early or in heavy soil. Fungicide seed treatments on most
commercially sold seed are there to protect seed from rot and are very
useful. Farmers should consider having seed treated with extra fungicide as an alternative to use of an infurrow applied fungicide.
- Plant in fertile soil. Seedling emergence is retarded in acidic
soils (pH less than 5.5) or alkaline soils (pH greater than 7.0), or soils
low in phosphorus or potassium. Starved, slow-growing seedlings are more
susceptible to damage by seedling diseases. Growers should make sure that
soil nutrient levels and pH levels in their fields are adequate for best
cotton growth and yield.
- Seedling diseases are worse when the soil is cold and wet. In
general, the top of a raised bed is dryer and warmer than flat soil. To
minimize seedling disease, plant on raised beds to maximize drainage and
the soil temperature of the seed bed. Make sure field drainage is adequate
to eliminate excesswater quickly, and break hard pans to improve internal
- When planting early or in poorly drained clay soil, use an in-furrow
fungicide for extra
protection against organisms that cause seedling diseases. The
fungicides applied to seed by the seed supplier help protect the seed and
seedling against rot (see Step 2), but will not protect the seedling from
all diseases. A fungicide applied to seed in
the furrow at planting (click here for list) will provide additional protection
against seedling diseases.
In-furrow applied fungicides are available in granule or liquid
formulation. The use of in-furrow fungicides has significantly increased
stands in tests conducted at the University of Missouri Delta Center.
- Use a device to move trash away from the row when planting no-till, so the
sun will warm the soil around the seed faster.
Following these suggested prodecures will give cotton farmers a better change
to produce high yields and profit. More information is available on the MU
Delta Center website at http://aes.missouri.edu/delta/
To order, request G04254 Cotton Seedling Diseases: Answers to
Frequently Asked Questions (25 cents).
* Issued in furtherance of Cooperative Extension Work Acts of May 8 and
June 30, 1914, in cooperation with the United States Department of
Agriculture. Ronald J. Turner, Director, Cooperative Extension Service,
University of Missouri and Lincoln University, Columbia, Missouri 65211. *
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