Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici. The earliest symptoms are the yellowing of the oldest leaves, generally on only one side of the plant. Wilting eventually affects the entire plant, causing collapse and death.

Discoloration of the vascular tissue due to Fusarium oxysporum f. sp. lycopersici. The pathogen blocks flow of water and nutrients through the stem, resulting in wilting of part of or the entire plant. Image courtesy of Clemson University - USDA Cooperative Extension.