Deep plowing approximately 12 inches with mold board plow, planting early maturing varieties to escape disease, addition of organic matter or green manure and crop rotation have proven to be the most effective control methods. Controls include management and cultural practices as no chemical treatment has been found that economically controls cotton root rot. These are 2-12 inches in diameter, first snow-white and cottony, later tan and powdery. Under moist conditions spore mats may appear on the soil surface near diseased plants. Fine, light brown strands of fungal threads (rhizomorphs) are usually found on the roots. Vascular streaking is not present as in the wilt disease. If examined soon after death, the stems will be near normal color internally. Scraping the taproot reveals a darkened, reddish to wine-colored stain. The root system of affected plants decay. The disease kills plants in circular areas ranging from a few square yards to an acre or more in size. Usually, the leaves of the plant are not shed, but remain attached. It causes rapid wilting, followed by death of the plants within a few days (Figure 3). Plowing under plant residues and crop rotation also aid in reduction of the disease.Ĭotton Root Rot (fungus – Phymatotrichum omnivorum): Root rot appears suddenly, starting in early summer. Use of acid delinted seed and suitable seed treatment fungicides will minimize carry-over. The fungus may be seed-borne but it primarily survives in the soil on the infected plant residue. Under conditions favorable for the disease, the lesions may completely encircle the stem or branch and kill the plant above the lesions. On stalks and branches, the lesions are dark brown, elongated and slightly sunken cankers. Defoliation may result from large lesions that coalesce. The lesions often occur at the base of the petiole. Later, the center of the lesions become ashy in color and may fall out. First, small, round, reddish-brown spots with a dark brown border appear on the leaves. The disease occurs on the leaves, stems and branches. The damage is generally spotty and many plants recover when dry, warmer weather returns. Serious outbreaks of the disease may follow extended rainy periods with serious defoliation occurring. An entire stand may be lost as a result of the fungus attacking the hypocotyl and killing the plant. Both seedlings and older plants are susceptible, but younger cotton is more seriously injured. Ascochyta or Wet Weather Blight – (fungus – Ascochyta gossypii): The disease is prevalent in most cotton producing areas of the state.
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