Disease | Symptoms | Cause | Comments | Management |
Cutworms ( Black cutworm, Variegated cutworm )(Agrotis ipsilon Peridroma saucia ) | Stems of young seedlings may be severed at soil line, larvae causing damage will be active in night and hide during day, larvae will exhibit different pattern and curl into C-shape when disturbed | Insect | Insects outbreak favored by cool, wet spring followed by a mild winter, cutworms have a wide host range and attack vegetables including asparagus, bean, pea, potato etc., | Remove all residue from soil after harvest or at least two weeks before planting, appropriate insecticide recommended, if not grown organically |
Aphids ( Cotton Aphid ) (Aphis gossypii) | Soft body insects found under the leaves, green or yellow in color depending on the species and host plant, if aphid infestation is heavy it may cause leaves to yellow and stunned shoots | Insect | Honey dew excreted by aphids promotes the growth of mold | Insecticides are are recommended, if aphid infestation is high, plants generally tolerate medium level |
Cotton bollworm( Helicoverpa Zea) | Holes chewed in bases of bolls and insects frass around holes | Insects | Adult insect is a pale green to tan, medium sized moth | Monitor plants for eggs and young larvae, appropriate chemical treatment may be required for commercial plantations |
Armyworm( Spodoptera exigua ) | Heavy feeding by young larvae leads to skeletonized leaves, dry wounds on fruits | Insects | Insects go through 3 – 5 generations a year | Organic methods of controlling armyworms include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis |
Fusarium Wilt( Fusarium Oxysporum ) | Wilting of cotyledons and seedling leaves, older plants exhibit symptoms of wilting and leaf chlorosis | Fungus | Disease favoured by warm temperature, fungus may spread due to infected seed or human movement | Use certified disease free seed, fumigating the soil may reduce disease incidence |
Alternaria leaf spot(Alternaria macrospora ) | Small and circular brown lesions on cotyledons and seedling leaves which expand and develop a concentric pattern | Fungus | Nutrient deficiency, plant stressed by drought and other pests are more susceptible to the disease | Provide plants with adequate irrigation and nutrients, Potassium application may be required on susceptible cultivars |
Cercospora leaf spot( Cercospora gossypina ) | Circular red lesion on leaves which enlarge and turn white or grey in the center | Fungus | Fungus overwinters in crop debris from previous growing season | Application of appropriate fungicide may be required on susceptible cultivars, adequate irrigation and nutrients recommended |
Bacterial blight( Xanthomonas campestris ) | Water soaked spots on leaves which are delimited by leaf veins giving them an angular appearance, lesions increase in size and turn black and necrotic | Bacterium | Disease often introduced by infested seeds | Use of resistant cotton varieties is the most effective method of controlling the disease |
Asochyta blight( Asochyta gossypii) | Brown or grey spots on leaves surrounded by a red halo | Fungus | Disease favored by cool, wet weather | No fungicides are currently registered for use in cotton, plow crop debris into soil after harvest |
Pests and Disease Management in Cotton
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