Verticillium wilt of cotton is caused by a fungus (Verticillium dahliae) that infects the host plant via the roots and colonises the vascular system. Symptoms therefore include a brown discoloration of the vascular tissue within the stem, branches and petioles and a yellowing and death of leaf tissue especially between the veins. The pathogen survives the intercrop period in association with infected crop debris or susceptible weed hosts. Verticillium wilt is favoured by cool soil conditions and symptoms are therefore most obvious in late spring and autumn. Yields may be reduced by up to 25% in seasons when environmental conditions favour the disease.