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Portageville, Pemiscot County
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*Our next field day will be held September 2, 2008.
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Director:
Jake Fisher
P. O. Box 160
Portageville, MO 63873
Phone: 573-379-5431
Fax: 573-379-5875
Email:FisherJ@missouri.edu
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Reviewed March, 2008
COTTON DISEASE MANAGEMENT
Allen Wrather, Plant Pathologist,
and Gene Stevens,
Commercial Agriculture
Agronomist, University of Missouri
The four most important strategies for cotton disease
management are to rotate crops, to plant resistant varieties, to
plant in warm and well-drained soil and to use fungicides when
necessary. An integrated approach (the use of all methods is the
most effective and profitable).
Resistant varieties: Varieties immune to all or most cotton
diseases do not exist. However, newer varieties often have
improved levels of resistance. Growers should choose varieties
based on MU yield trials in their area and resistance to locally
important diseases.
Crop rotation: Rotating crops will help manage several diseases
of cotton. For example, the number of root knot nematodes in the
soil declines when a root knot nematode-resistant soybean
variety is planted. The population of this nematode will fall
below the cotton damage threshold after planting a resistant soybean for a
few years. The grower can then resume planting cotton but should
continue rotation to keep the nematode problem minimized.
Planting in warm soil: Seedling diseases of cotton are worse
when the soil around the seed and seedling is cool and wet. Seed
and seedling death can result in severely reduced stands and
reduced yields. Surviving plants have a stunted root system and
yield poorly. Growers should avoid planting in cool wet soil and
when the weather forecast indicates that cool wet conditions may
develop within 5-7 days of planting.
Fungicides: Fungicide seed treatment are very helpful in
managing seedling diseases. Commercially sold cotton seed in the
United States is treated with fungicides. Fungicides applied
infurrow may be useful when planting cotton, especially when
planting in late April and in soil that is poorly drained (see
following for labeled fungicides and rates).
Additional information: An accurate diagnosis of plant disease is
essential before selecting a management technique for next year.
Whenever possible, consult an expert in plant disease diagnosis.
This section is not intended to aid identification of cotton
diseases, but is intended to be a rapidly accessible source of
information on management techniques. MU publications Cotton
Seedling Disease, G4254, and Cotton Nematodes in Missouri: Your
Hidden Enemies, G4259; have more information on cotton disease
identification and management. They are available at your local
extension center or Extension Publications, 2800 Maguire Blvd.,
Columbia, MO 65211 and are on the World Wide Web
(aes.missouri.edu/delta).
The publication was made possible through the efforts of many
people, including Joyce Elrod, senior research technician at the
MU Delta Center.
| Disease
| Symptoms
| Registered Pesticides
| Remarks
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Bacterial blight
Xanthomonas campestris pv. malvacearum
| Small, light green to dark brown angular lesions on leaves. Large numbers of lesions may darken large areas of a leaf. Infected leaves defoliate prematurely. Symptoms rarely occur on bolls or stems in southeastern Missouri
| None
| Most varieties have some resistance. Crop rotation will control this problem.
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Boll rots
Ascochyta gossypii, Glomerella gossypii, Diplodia gossypina, Fusarium species, Phomopsis species, Phytophthora capsici, Xanthomonas campestris pv. malvacearum
| Small, brown lesions on bolls expand and the entire boll may eventually become blackened and dry.
| None
| Prolonged periods of high humidity or water on the boll surface is necessary for infection. Rank growth promotes boll rot. Avoid practices that result in a rank dense canopy, such as avoiding a final population of more than 3 plants per foot row, and excess nitrogen. Use a growth regulator, such as Pix, to reduce height.
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leaf spots
Alternaria macrospora
| Small, brown and circular lesions on leaves enlarge to 0.4 inches. Old lesions have grey centers that may fall out.
| None
| These leaf spot diseases are of minor importance and specific controls are not recommended. Farmers should manage their crop for best economic yield, such as rotation.
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Leaf spots
Cercospora gossypina
| Small purple lesions on leaves expand to light-brown lesions surrounded by narrow purple margin. Old lesions may be 0.7 inches in diameter.
| None
| Stressed plants are prone to this disease. So, use proper amounts of fertilizer, provide drainage, irrigate when needed and use a growth regulator.
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Leaf spots
Ascochyta gossypii
| Small (2mm) brown lesions on leaves that enlarge into irregular dead areas surrounded by a dark brown border. Lesion centers may crack and fall out.
| None
| As above.
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Leaf spots
Alternania sp.
| Small purple spots develop on dying leaves. These lesions resemble those caused by Cercospora, but the center of these lesions remain purple.
| None
| As above.
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Seedling disease
Rhizoctonia Fusarium and Pythium spp.
| Slow emergence, thin stand, lesions on stems at soil line, dry or soft rot of roots and lodged seedlings.
| Apply one of the following in-furrow fungicides during planting (click here for list).
| . Plant only high-quality (more than 80 percent germination) fungicide treated seed. Plant in warm, well drained soil. Avoid crop stress due to a lack of fertilizer, excess water or excess herbicides. Plant on raised beds.
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Wilt, Fusarium
Fusarium oxysporum f. sp. vasinfectum
| Symptoms usually first appear on oldest leaves at bloom. Areas of leaf margin wilt, then turn yellow. Eventually, entire leaf may wilt and turn yellow. Leaves defoliate prematurely. A brown layer of tissue appears just below the bark of lower stem. Bolls may open prematurely. These symptoms are difficult to distinguish from Verticillium wilt.
| None
| Most varieties are somewhat resistant. Maintain soil pH at 6.0 to 6.5. Maintain high soil levels of phosphorus and potassium.
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Wilt, Verticillium
Verticillium dahliae (formerly V. albo-atrum)
| Irregular yellow areas appear between veins and on margins of oldest leaves first. Centers of yellowed areas may turn brown. Defoliation is slow. Plants are usually stunted and vascular discoloration occurs. Bolls may open prematurely.
| None
| Plant tolerant varieties, maintain soil pH 6.0 to 6.5 and use recommended rates of nitrogen and potash.
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Lance nematode
Hoplolaimus spp.
| Above-ground symptoms same as root-knot nematodes. Plant may defoliate following drought. Small, brownish-yellow lesions on roots.
| Same as for root-knot nematode.
| Same as for root-knot nematode.
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Reniform nematodes
Rotylenchulus reniformis
| Light green color appears by the third or fourth leaf stage. Leaf margins may become purple. Other above-ground symptoms same as root-knot nematodes. Root systems reduced and may be discolored.
| Same as for root-knot nematode.
| Same as for root-knot nematode.
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Root-knot nematode
Meloidogyne spp.
| Above-ground symptoms depend on the level of infestation. At high levels there may be stunting, yellowing and an unthrifty appearance. Plants may wilt in the heat of the day and recover at night. Yields are reduced. Symptoms may be confused with mineral deficiency, drought, herbicide injury or other soilborne diseases. Symptoms occur in oval patches or spaced erratically through the field. Roots have small to large galls and may be branched excessively. Roots are usually discolored.
| The following chemicals are labeled for nematode control (click here for list).
| Root-knot nematodes are involved in diseases complexes with wilts and seedling diseases. Rotation with small grains or other grasses and some soybean varieties may reduce nematode numbers. Other rotations depend on the species present. No highly resistant cultivars are available.
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* 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. * University
Extension does not discriminate on the basis of race, color, national origin,
sex, religion, age, disability or status as a Vietnam-era veteran in
employment or programs. * If you have special needs as addressed by the
Americans with Disabilities Act and need this publication in an alternative
format, write ADA Officer, Extension and Agricultural Information, 1-98
Agriculture Building, Columbia, MO 65211, or call (573) 882-8237. Reasonable
efforts will be made to accommodate your special needs.
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