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Protocol: Late blight rating system (modified from James, C. 1971)

rating 1

Rating2.GIF (48257 bytes)



0.001% 1 lesion per quadrat
0.01% 2-5 leaves per 10 plants affected. About 5 large lesions per quadrat
0.1% About 5-10 infected leaflets / plant; OR about 2 affected leaves / plant
1.0% General light infection. About 20 lesions / plant OR 10 leaves affected / plant; 1 in 20 leaves affected severely
5.0% About 100 lesions / plant; 1 in 10 leaflets affected (up to 50 leaves affected)
25% Nearly every leaflet infected but plants retain normal form; plants may smell of blight. Field looks green although every plant is affected
50% Every plant is affected and about 50% of the leaf area is destroyed. Field appears green flecked with brown
75% About 75% of the leaf area destroyed; field appears neither predominantly green nor brown
95% Only a few leaves on plants, but stems are green
100% All leaves dead, stems dead or dying

Adapted from: James, C. 1971. A manual of assessment keys for plant diseases. Canada Department of Agriculture. Publication No. 1458.

infected tubers

infected tomatoes