How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms of summer black stem and leaf spot usually appear after the alfalfa has grown a dense canopy. Defoliation from the base of the stem to the top is the most obvious symptom, but leaf spots usually appear first. Leaf spots begin as brown areas with a wavy margin. As spores on the surface of the spot are produced, the color of the spot appears gray or silvery. A diffuse yellow margin often surrounds the spot. Brown lesions also form on stems. High humidity (close to 100%) and temperatures ranging from 75 to 82°F favor disease development.

COMMENTS ON THE DISEASE

Summer black stem is a disease of limited importance and has been observed primarily in the Imperial Valley.

MANAGEMENT

Harvest early before extensive defoliation occurs to minimize losses.

PUBLICATION

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430
Diseases
R. M. Davis, Plant Pathology, UC Davis
C. A. Frate, UC Cooperative Extension, Tulare County

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