Cotton:Key

KEY TO COTTON PESTS AND NUTRITIONAL DISORDERS

Seed

Seed disorders are limited to disorders while in the ground and not to potential disorders inherent in the seed.

No Distinct Discoloration

Seed rot

Pregermination decay of planted seed

Seedling

BLACK

Black root rot

Black layer of decayed tissue, mostly on the surface of seedling roots, sometimes on roots of older plants

BROWN

Cold damage

Marginal to complete killing of seedling leaves; damage may be worse in lower parts of the field

Seedling disease complex

Postemergence damping-off; yellow, reddish brown, or brown decayed zones on the hypocotyl of the seedling; if the decay is girdling, seedling may topple over and die

GREEN

Wet-weather blight

Irregular dead areas in cotyledons, spreading in damp, cool weather to consume entire seedling; if spread is arrested by drying conditions, dead areas may fall out, leaving cotyledons with a ragged appearance

RED

Seedling disease complex

Postemergence damping-off; yellow, reddish brown, or brown decayed zones on the hypocotyl of the seedling; if the decay is girdling, seedling may topple over and die

YELLOW

Seedling disease complex

Postemergence damping-off; yellow, reddish brown, or brown decayed zones on the hypocotyl of the seedling; if the decay is girdling, seedling may topple over and die

No Distinct Discoloration

Crusting of soil after planting

Delayed seedling emergence; torn or distorted seedlings

Soil crusting; windblown sand; hail damage

Mutilation and distortion of seedlings

Windblown sand injury

Rapid desiccation of seedlings; water-soaked spots on young seedlings; retarded growth; death of seedlings in severe cases

Root

BLACK

Charcoal rot

A dry rot of all root tissues; plants wilt suddenly; most common in drought-stressed cotton

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

BROWN

Compaction of soil in root zone

Poor root development; dwarfed plants; wilting during drought stress

Phymatotrichum root rot

Half-grown plants wilt suddenly, do not recover; neighboring plants wilt and die, until a spot of dead plants forms in the field; a newly wilted plant has a decayed taproot, with the dirty, yellowish brown weft of the causal fungus on the surface

GRAY

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

WHITE

Sclerotium stem and root rot

Sudden wilting and death of seedlings, associated with decay of upper root system and lower stem; white mold growth surrounds hypocotyls when soil is wet

YELLOW

Phymatotrichum root rot

Half-grown plants wilt suddenly, do not recover; neighboring plants wilt and die, until a spot of dead plants forms in the field; a newly wilted plant has a decayed taproot, with the dirty, yellowish brown weft of the causal fungus on the surface

No Distinct Discoloration

Lance nematode

Foliar chlorosis and stunting, sometimes followed by defoliation

Reniform nematode

Plants severely stunted; foliage sometimes chlorotic; plants may wilt; small feeder roots destroyed; yield often reduced as much as 60%

Root-knot nematode

Plants unthrifty; often numerous beadlike swellings along the roots

Sting nematode

Severe chlorosis and stunting, followed by early death of plants; infested roots have small, sunken spots of dead tissue, become stubbed and decayed

Stem

BLACK

Bacterial blight

Dark green water-soaked cankers on stems, later becoming black in the center with red border; where the canker becomes girdling, the distal part of the stem dies

BROWN

Bacterial blight

Water-soaked spots up to 6 mm in diameter in the seedling leaves, turning dark brown upon drying, often showing slimy bacterial accumulation on surface, later drying to waxy crusts

DARK

Bacterial blight

Dark green water-soaked cankers on stems, later becoming black in the center with red border; where the canker becomes girdling, the distal part of the stem dies

GREEN

Bacterial blight

Dark green water-soaked cankers on stems, later becoming black in the center with red border; where the canker becomes girdling, the distal part of the stem dies

Manganese toxicity

Crinkled, distorted leaves; shortened internodes; and dwarfing, all tending to be severe in very acid soils

RED

Bacterial blight

Dark green water-soaked cankers on stems, later becoming black in the center with red border; where the canker becomes girdling, the distal part of the stem dies

TAN

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

WHITE

Sclerotium stem and root rot

Young plants wilt suddenly and die when soil is waterlogged; with continued damp conditions, the causal fungus flares out from the dying plant as a white, fanlike mold growth on the soil surface

YELLOW

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

No Distinct Discoloration

Acromania

Abnormally upright habit of growth; upper branches barren

Hail damage

Plant laceration and crushing

Leaf

BLACK

Charcoal rot

A dry rot of all root tissues; plants wilt suddenly; most common in drought-stressed cotton

Sulfur dioxide injury

Gray green, water-soaked zones in the foliage, later becoming brown to black

BLUE

Blue disease

Apical leaves bulge toward the base; leaf blade at first light green; entire leaf later becomes deep bluish green; symptoms occur only on parts of the plant that develop after infection is initiated

BROWN

Alternaria leaf spot

Nearly circular leaf spots up to 6 mm in diameter, with reddish brown dead centers and dark brown margins

Anthracnose

Dark brown cankers on stem, older ones showing mold growth on the surface, often with pustules full of slimy pink masses of spores

Bacterial blight

Water-soaked, angular dead areas in the leaf blade or along principal veins; diseased areas may be coated with slimy bacterial exudate; dead areas turn dark brown and dry, leaving exudate as white waxy crusts on leaf surface

Boron deficiency

Terminal buds die, leading to rosette effect in top of plants; older leaves may be thick and leathery

Cold damage

Marginal to complete killing of seedling leaves; damage may be worse in lower parts of the field

Escobilla

Leaves reduced in size, densely crowded in tufts produced by abnormal forcing of axillary buds, creating a witches' broom effect; dead zones in some leaves

Sulfur dioxide injury

Gray green, water-soaked zones in the foliage, later becoming brown to black

Tropical rust

Yellowish brown pustules break through the upper and lower leaf surfaces; sometimes groups of pustules occur on purple zones of dead leaf tissue; infected leaves tend to drop prematurely

DARK

Anthracnose

Small dark spots on cotyledons or hypocotyls, which in damp weather may spread to the entire seedling and kill it

Phosphorus deficiency

Abnormally dark green leaves; dwarfing

GRAY

Sulfur dioxide injury

Gray green, water-soaked zones in the foliage, later becoming brown to black

GREEN

Areolate mildew

Angular infected spots, pale green on upper surface, covered with dense white masses of mildew growth on lower surfaces, appearing toward end of growing season

Blue disease

Apical leaves bulge toward the base; leaf blade at first light green; entire leaf later becomes deep bluish green; symptoms occur only on parts of the plant that develop after infection is initiated

Leaf crumple

Leaf tissue between veins grows excessively, causing cupping and a blistered appearance; bracts and flowers show distortion; symptoms most severe on new growth arising from ratooned cotton

Leaf curl

Thickening of small and large veins; finlike outgrowths from veins

Phosphorus deficiency

Abnormally dark green leaves; dwarfing

Phyllody

Leaves distorted into stringlike or straplike shapes

Sulfur dioxide injury

Gray green, water-soaked zones in the foliage, later becoming brown to black

Vein clearing

Green color disappears from leaf veins; deep green bands later appear along main veins; young leaves tend to cup downward

LIGHT

Potassium deficiency

Yellowish white foliar mottling; light spots take on a rusty appearance; premature defoliation

ORANGE

Southwestern cotton rust

Orange, pointlike eruptions on upper surface of cotyledons; clusters of orange cuplike structures on lower surfaces

PINK

Anthracnose

Dead areas circular or irregular in outline; with continued damp weather, areas enlarge to consume large parts of the leaf; may form moldlike growth and pinkish slimy masses of spores on surfaces of older lesions

Anthracnose

Dark brown cankers on stem, older ones showing mold growth on the surface, often with pustules full of slimy pink masses of spores

PURPLE

Magnesium deficiency

Reddish purple leaves, veins remaining green

Minor leaf spots

Small dead spots up to 3 mm in diameter, variously colored, often with purplish margins, usually appearing on senescing plants

Tropical rust

Yellowish brown pustules break through the upper and lower leaf surfaces; sometimes groups of pustules occur on purple zones of dead leaf tissue; infected leaves tend to drop prematurely

RED

Alternaria leaf spot

Nearly circular leaf spots up to 6 mm in diameter, with reddish brown dead centers and dark brown margins

Magnesium deficiency

Reddish purple leaves, veins remaining green

Misuse of arsenicals

Reddened foliage, especially at margins of leaves where spray collects

Nitrogen deficiency

Yellowing, eventual reddening of foliage; plants may be dwarfed

TAN

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

WHITE

Areolate mildew

Angular infected spots, pale green on upper surface, covered with dense white masses of mildew growth on lower surfaces, appearing toward end of growing season

Bacterial blight

Water-soaked, angular dead areas in the leaf blade or along principal veins; diseased areas may be coated with slimy bacterial exudate; dead areas turn dark brown and dry, leaving exudate as white waxy crusts on leaf surface

Potassium deficiency

Yellowish white foliar mottling; light spots take on a rusty appearance; premature defoliation

Powdery mildews

Dense accumulation of white mildew and spores on upper or lower leaf surface; leaves are sometimes curled and defoliation may ensue

YELLOW

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

Compaction of soil in root zone

Poor root development; dwarfed plants; wilting during drought stress

Lance nematode

Foliar chlorosis and stunting, sometimes followed by defoliation

Manganese toxicity

Crinkled, distorted leaves; shortened internodes; and dwarfing, all tending to be severe in very acid soils

Misuse of substituted urea compounds or triazines

Yellowing, mottling, and death of young seedlings

Mosaic

Chlorotic mottling and cupping of foliage

Nitrogen deficiency

Yellowing, eventual reddening of foliage; plants may be dwarfed

Potassium deficiency

Yellowish white foliar mottling; light spots take on a rusty appearance; premature defoliation

Reniform nematode

Plants severely stunted; foliage sometimes chlorotic; plants may wilt; small feeder roots destroyed; yield often reduced as much as 60%

Sulfur deficiency

Yellowing of top leaves; lower leaves remain green

Tropical rust

Yellowish brown pustules break through the upper and lower leaf surfaces; sometimes groups of pustules occur on purple zones of dead leaf tissue; infected leaves tend to drop prematurely

No Distinct Discoloration

Acromania

Abnormally upright habit of growth; upper branches barren

Hail damage

Plant laceration and crushing

Flower

TAN

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

YELLOW

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

Fruit

BROWN

Bacterial blight; Anthracnose; Various fungi

Decays of various colors, mostly caused by species of molds, attacking bolls in different stages of development, destroying them partly or completely, or preventing proper opening of the boll or fluffing of the lock

TAN

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

YELLOW

Fusarium wilt; Verticillium wilt

Plants dwarfed; foliage exhibits patterns of chlorotic mottling; daily wilting, with nightly recovery of plant turgor; woody part of roots, stems, petioles, and often peduncles of flowers and fruits discolored with streaks of yellow, tan, gray, or black

Bacterial blight; Anthracnose; Various fungi

Decays of various colors, mostly caused by species of molds, attacking bolls in different stages of development, destroying them partly or completely, or preventing proper opening of the boll or fluffing of the lock