Rust of Cotton

Rust is the most importent foliar disease. It was described from Baja califer nia, Maxico in 1983 abd from Arizona in 1922. The disease occurs only in certain parts of Southern Arizona, New Mexico, West Texas, Northern Mexico and India. It also infects on grama grass. Yield loss up to m15-20 percent reported.

Etiology

            It produces septate hyphae from which conidiophores arise. The conidiophores are short, septate, branched at the base and measure 50-150 x 4.5-7 µ. The conidia are borne singly or in short chains at the tip of the conidiophores and are colourless, irregularly oblong with pointed, rounded or flattened ends.

Disease cycle

             The disease spreads mainly through air borne conidia. The method of perpetuation during the off season is unknown.

      Symptoms on leaves                         Whole plot infected with rust

Epidemiology

            Leaf wetness periods in excess of 16 hours coupled with high humidities and moderate temperatures are factors necessary for epidemics to occur.