Spot Blotch (Cochliobolus sativus)

Spot Blotch: biology

The pathogen survives on crop residue on which it produces airborne spores. The spores can also survive for a long time in soil. Warm wet weather favors spot blotch. The disease can be seed-borne.

Spot Blotch: damage description

Spot Blotch

Initially small brown spots occur on leaves. These expand to larger dark brown blotches. The blotches may be surrounded by a yellow zone. The fungus causing spot blotch also causes seedling blight, common root rot and kernel smudge (black point).

Yield loss is due to shrivelled seed and reduced seed set.

Spot Blotch: management

Allow one or preferably a two-year break between susceptible crops. If available, use varieties which have some resistance. Burying residue may reduce disease incidence. Foliar-applied fungicides will reduce losses but crops should be monitored closely around flag leaf emergence and sprayed when only small spots are present on upper leaves. Seed treatments reduce seed transmission but will not protect plants from spores produced on crop residue which is typically the source of inoculum for spot blotch.