Description and Symptoms
Goss’s wilt and leaf blight (Clavibacter michiganensis subsp. nebraskensis) has reemerged as an important disease of corn in recent years. Leaves can be infected 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 a tan color. 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.
The best time to scout is VE through R6. Confused with other diseases and abiotic stresses like northern leaf blight and sun scorch. Northern leaf blight has distinct margins whereas Goss's wilt lesions show a transition from dead to yellowing to healthy tissue. Typically starts in the mid- to upper canopy, often first observed at VT or RI.
As with all diseases, correct diagnosis is important to enable appropriate management practices to be followed. For Goss’s, tolerant hybrids is by far the best management tool we have at present. There are numerous foliar applied products being marketed for Goss’s management. Several field trials are being done here in Iowa, and also neighboring states, to evaluate the efficacy of these products.
Resistant hybrids are available. Crop rotation and tillage reduce survival of Clavibacter michiganensis subsp. nebraskensis. Fungicides are not effective against this disease.
Photo by Adam Sisson