Cotton Seedling Diseases
Cotton Disease Information Note No. 1
Steve Koenning, Plant Pathology Extension Specialist
1. A poor stand of cotton seedlings.
Seedling diseases (Figure 1) cause an estimated average annual yield loss
of 5% and are usually the major disease problems in cotton production in
North Carolina. Several soilborne fungi are responsible; however, cultural
and environmental factors that delay seed germination and seedling growth
make the problem more severe.
Environmental Factors Influencing Seedling Diseases
Seedling disease occurs more frequently under cool, wet conditions and seems
to be more prevalent on sandy, low-organic-matter soils. Environmental factors
are very important in influencing the development of seedling diseases (Table
1). Other factors, such as planting too deep, poor seed bed conditions,
compacted soil, nematode or insect infestations, and misapplication of soil-applied
herbicides such as dinitroanalines, may increase the problem. Seedling diseases
tend to be more severe in reduced tillage situations and when beds are absent.
Planting on beds elevates the seed allowing for more rapid emergence, especially
after heavy rains. Plants are more prone to attack by pathogens when stressed
by an inhospitable environment, insects, or other causes. As a result, contagious
diseases are often associated with insect infestations and poor growing
conditions. Damage from thrips in particular can delay seedling development
and enhance damping-off diseases caused by various fungi.
Fungi Causing Seedling Diseases
of fungi can cause seedling disease, but the primary agents are Rhizoctonia
solani, Pythium spp., Phoma exigua (Ascochyta),
and Fusarium spp. These disease causing organisms can attack the
seed before or at germination. They also can attack the young seedling before
or after emergence. Symptoms include seed decay, decay of the seedling before
emergence, partial or complete girdling of the emerged seedling stems, and
seedling root rot. Seed and seedling disease is characterized by a soft,
watery rot. Damaged seedlings that
emerge are pale, stunted, slower growing, and sometimes die within a few
days. Examination of infected seedlings may reveal dark lesions on the stem
and root. Often the taproot is destroyed, and only shallow-growing lateral
roots remain to support the plant. The "sore shin" phase of seedling disease
is characterized by reddish brown, sunken lesions at or below ground level
(Figure 2). These lesions enlarge, girdle the stem, and cause it to shrivel.
Seedling diseases do not usually kill the entire seedling population, but
rather result in uneven, slow-growing stands with skips in the rows. In
some years, replanting is necessary. Poor stand establishment causes problems
with the management of other pests and may reduce yields.
2. sore shin of
The most common fungi associated with seedling diseases in North Carolina
are Pythium spp. and Rhizoctonia solani. Often both fungi
can be found on the same seedling. The same fungus may cause seed decay,
seedling root rot, or both. However, Pythium spp. and Fusarium
spp. usually attack the seed and below-ground parts of young seedlings,
while R. solani usually causes sore shin. Rhizoctonia solani
and P. exigua may attack seedlings from the time they emerge until
they are about 6 inches tall. After this stage, the stem becomes woody,
and subsequent infection rarely occurs unless the stem is injured.
Several species of fungi in the genus Pythium can cause seedling
disease in cotton as well as several other crops. Pythium spp.
are generally classified as water molds. These fungi produce spores
that can actively move in soil water. In general, Pythium is
more commonly the causal fungus if the soil has remained saturated for
several days or is poorly drained. Mefenoxam (Ridomil Gold) or Etridiazole
(ETMT, Terrazol) are necessary to control seedling disease caused by
This fungus typically causes sore shin, and is more common on sandy,
well-drained soils. Plants injured by sand blasting are particularly
susceptible to this pathogen (Figure 2). Fungicides containing PCNB
(Terrachlor) or Iprodione (Rovral) are generally effective against Rhizoctonia
Phoma exigua (Ascochyta gossypii)
3. Post-emergence damping off caused by Phoma exigua.
can cause post-emergence damping off. This disease is characterized
dying of cotyledons which turn brown and shrivel (Figure 3). This disease
has been observed when night temperatures are in the 50's and foggy
or misty conditions occur (see also Cotton
Disease Information Note No. 2). Fungicides have not been evaluated
as to their efficacy against this fungus.
Various species of fungal genus Fusarium are typically found
on diseased seedlings. Seed applied fungicides are generally effective
in managing Fusarium spp.
A control program for seed and seedling diseases is based on preventive
rather than remedial treatments. The program uses fungicides along with
cultural practices to make conditions more favorable for the young cotton
and less favorable for the disease-causing organisms. Poor quality seed
with low germination should be avoided.
Fungicides (Table 2) are a primary component
in a program to manage cotton seedling diseases. Be sure to plant only
fungicide treated seed. Using in-furrow fungicides may give further
benefits. Be sure to follow label recommendations since formulations
change from year to year. In particular, Ridomil Gold generally is applied
at lower rates than Ridomil.
All cotton seed offered for sale in North Carolina is treated with fungicides.
Seed treatments are categorized as protectants and systemics. Protectant
fungicides, such as captan or thiram, provide surface protection from
disease organisms carried on the seed and from organisms found in nearby
soil that cause seed rot. Systemic fungicides, such as carboxin (Vitavax)
or mefenoxam (Ridomil Gold), are absorbed through the seed coat of the
germinating seed and are taken up by the young seedling. Systemic fungicides
provide temporary protection from certain types of preemergence and
postemergence damping off. For specific fungicide recommendations and
formulations refer to the NC
Agricultural Chemicals Manual. In most years, seed treatment fungicides
are sufficient for controlling seedling disease, unless the quality
of the seed is low or weather conditions are unfavorable for germination.
If additional fungicide is desired, it is best to use an in-furrow treatment.
Hopper-box seed treatments are also available. However, coverage and
effectiveness are much better with in-furrow sprays or granules.
In-Furrow Fungicide Treatment
Protection obtained with seed treatment may not last long enough for
the cotton seedlings to grow to a stage where their susceptibility to
diseases is reduced. An in-furrow fungicide is suggested for fields
with a history of seedling disease problems, when planting early, or
when cool, wet weather is expected shortly after planting. In-furrow
treatments also are helpful if the seed quality is questionable. Fungicides,
however, are not a substitute for high-quality seed and good planting
conditions. In-furrow fungicides will not be profitable in most years;
however, if conditions are less than optimal, they can result in better
and more uniform stands. Better stands may translate into higher yields.
There are two methods for applying in-furrow fungicides: in-furrow sprays
or in-furrow granules.
An in-furrow spray is a very effective method, but it is not practical
for most growers who use their spray tanks and pump to apply preemergence
herbicides as they plant. For best results, apply the fungicide through
two cone-type nozzle tips. Mount the front nozzle just behind the seed
drop outlet to treat the soil around the seed. Direct the rear nozzle
to spray soil as it tumbles into the seed furrow with a small amount
of spray striking the top of the covered row.
Using an in-furrow granular fungicide is practical and effective. Nearly
all cotton planters already have one applicator box for systemic insecticide
applications. A second applicator is a relatively inexpensive addition.
If a second applicator cannot be added, combination treatments (insecticide
and fungicide on the same granule) may be available (check with your
dealer). Granules should be placed in the bottom of the seed furrow
and mixed with the covering soil.
Hopper Box Treatments
Soil fungicides cannot be applied very well by the hopper-box method
with acid delineated seed unless the seed and fungicide are properly
layered in the hopper box. When mixed well with seeds, some fungicide
will fall out with each seed to treat the soil around it. Fungicides
may reduce the seeding rate by 10 to 20 percent, so you must calibrate
the planter with the seed and fungicide mixture to get the desired rate.
The hopper-box method, while less expensive than in-furrow sprays and
in-furrow granules, however, is sometimes less effective. When used
properly, the hopper-box method may give better results than seed treatments
Additional Seed Treatments
The addition of more seed treatment to treated seed is not generally
recommended. This may result in more handling of seed that may cause
mechanical damage. Most cotton seed is treated with three or more fungicides
which are sufficient to protect against the spectrum of disease causing
fungi that commonly occur in North Carolina. Additional seed treatment
is likely to add more fungicide that is already present on the seed.
Table 1. Point system for determining the
need for in-furrow fungicides. This point system is only a guide as to the
probability of receiving a benefit from application of an in-furrow fungicide.
Temperature < 65
Day Forecast - Colder and wetter
Quality - Cold germ < 59%
History - Severe disease
- Minimum tillage
Preparation - Beds absent
Rate - Less than 3-4/foot of row
total exceeds 200, consider using an in-furrow fungicide
Table 2. Fungicides for control of cotton
seedling diseases. These materials are generally used in combinations. For
specific fungicide recommendations and formulations refer to the NC
Agricultural Chemicals Manual.
Ridomil Gold, Apron
Sore shin, Fusarium
Sore shin, Fusarium
subtillus (a bacterium)**
Sore shin, Fusarium
harzianum (a fungus)**
labeled for use on cotton.
**Little information on the efficacy of these biological pesticides is
Pest Management Strategic Plan for the MidSouth
Agricultural Chemicals Manual
Recommendations for the use of chemicals are included in
this publication as a convenience to the reader. The use of brand names
and any mention or listing of commercial products or services in this
publication does not imply endorsement by the North Carolina Cooperative
Extension Service nor discrimination against similar products or services
not mentioned. Individuals who use chemicals are responsible for ensuring
that the intended use complies with current regulations and conforms to
the product label. Be sure to obtain current information about usage and
examine a current product label before applying any chemical. For assistance,
contact your county North Carolina Cooperative Extension Service agent.
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