Verticillium Wilt (fungus -Verticillium albo-atrum): Young plants infected with Verticillium wilt show yellow leaves and stunting, and often die. Following the seedling stage, older plants exhibit a chlorotic mottling on the leaf margins and between the major veins. (Figure 4) Plants attacked during later stages of growth display a mottling on the lower leaves first, later progressing toward the top of the plant as the season progresses. Often a single branch shows symptoms in the early stages of disease. Yellow progresses inward, followed by brown, and the leaf finally dies. Severely affected plants shed all their leaves and most of their young bolls. These plants may survive throughout the growing season and send out young sprouts or shoots from the base of the plant. Verticillium wilt is difficult to distinguish from Fusarium wilt. Leaf symptoms are similar and the internal tissues of the stems are discolored in both diseases. The only reliable way to distinguish the wilts is through a laboratory isolation of the fungus. The fungus causing Verticillium wilt can survive in the soil as small, dark resting bodies called sclerotia. The sclerotia can withstand adverse environmental conditions. Susceptible plants growing in Verticillium infested soil may not be severely attacked if environmental conditions are not suitable for fungal growth. The disease is more prevalent during periods of cool, wet weather. The fungus is not transmitted in seed, but can be introduced in the field by infested gin trash and burrs. The disease is more common on heavier soils than on light sandy soils. Control measures include avoiding excess nitrogen, crop rotation, shallow cultivation to avoid root pruning, avoiding excess irrigation, and planting resistant varieties.
