Introduction About cotton Cotton diasesis

Fusarium Wilt (fungus – Fusarium oxysporum f. sp. vasinfectum): Fusarium wilt is more prevalent in the lighter-textured acid soils of Texas. Unlike Verticillium wilt, seeds from diseased plants can become infected and serve to spread the fungus. The fungus may attack cotton seedlings, but the disease usually appears when the plants are more mature. Affected plants are first darker green and stunted, followed by yellowing of the leaves and loss of foliage. First, symptoms appear on lower leaves around the time of first flower. The leaf margins wilt, turn yellow, then brown, moving inward. Infected plants fruit earlier than normal with smaller bolls that open prematurely. A diagonal cut across the stem will reveal vascular discoloration just beneath the bark extending down the tap root. Wilting occurs rapidly following a rain preceded by a dry spell. Soils in which Fusarium wilt occurs also favor root knot nematodes and the two are often found together. Reniform nematodes (which occur mostly in the lower Rio Grande Valley) also predispose the plant to attack by the fungus. Control of nematodes is of major importance in reducing Fusarium wilt. Cultural practices effective for reducing Fusarium wilt losses include avoiding seed from infested fields in humid climates, rotation with non-susceptible crops, use of in-furrow nematacides, and varieties with resistance.
Rust (fungus – Puccinia cacabata): True cotton rust is quite distinct from the “rust” caused by potash deficiency. Cotton rust is confined to the Trans-Pecos area of West Texas, where it may reduce yields as much as 50 percent. Rust first appears as small, yellowish spots or pustules on leaves, bracts, green bolls, and stems. These enlarge, developing orange to reddish centers. Later, large orange pustules appear on the lower leaf surface and discharge orange spores (aeciospores). Several lesions on a leaf may cause it to shed. The rust lesions will also weaken stalks, stems and petioles, causing breakage on these parts. Broken stalks are more difficult to cultivate and harvest mechanically. The aeciospores released on the cotton do not reinfect cotton, but are windblown to wild gramma grass, which serves as an alternate host for the fungus. (Figure 7). A rainfall of « inch or more, followed by 12 – 18 hours of high humidity, is needed in June or early July for disease development. The only effective means of control is with an application of a mancozeb foliar fungicide before the cotton is infected. This is the only labeled fungicide, but it can not control the fungus after infection has occurred.