Goss’s wilt of corn
Goss’s wilt is caused by the bacteria Clavibacter michiganensis subsp. nebraskensis, which can infect leaves at any stage of plant growth. Leaf lesions are long, gray-green to black, water-soaked, and have wavy edges. Streaks resembling freckles within the lesions are a distinctive symptom of this disease. Droplets of bacterial exudate eventually ooze from these freckles. As the droplets dry, they leave crystalline deposits on the leaf surface. Lesions may join together to blight much of the leaf. As the lesions age, they gradually lose the gray-green color and fade to tan. Systemically infected plants may have discolored vascular tissue – a wet, slimy stalk rot – and may wilt as if drought stressed.
The bacterium overwinters in infected corn residue and is spread by splashing water and in very fine, airborne particles. Seed can be infected but is not believed to be an important means of dissemination. The bacteria enter the corn plant through stomates (natural leaf openings allowing air exchange) or through wounds caused by hail, blowing soil, or wind.
Resistant hybrids are available. Crop rotation and tillage reduce survival of C. michiganensis subsp. nebraskensis. Fungicides are not effective against this disease.
Gallery Images: K. Wise, E. Zaworski, C. Grau, A. Robertson, and A. Sisson