An interaction is an association between two or more pests which results in greater plant damage than if either pest occurred alone. For cotton, the most common interactions occur between; nematodes (root-knot, reniform, and lance) and seedling disease fungi (Thielaviopsis basicola, Fusarium spp., Rhizoctonia solani and Pythium spp.) or seedling disease fungi or nematodes and insects (thrips or white flies). Disease interactions can be additive, meaning the sum of disease severity is equal to the severity of disease caused by either pest alone or synergistic, meaning the severity of damage is greater than the sum of damage caused by either pest.