How to Manage Pests

UC Pest Management Guidelines


Summer Black Stem and Leaf Spot

Pathogen: Cercospora medicaginis

(Reviewed 3/17, updated 3/17)

In this Guideline:

Symptoms and signs

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. Disease development is favored by high humidity (close to 100%) and temperatures ranging from 75 to 82°F.

Comments on the Disease

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


Harvest early before extensive defoliation occurs to minimize losses.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430


R. M. Davis, Plant Pathology, UC Davis (Emeritus)
C. A. Frate, UC Cooperative Extension, Tulare County (Emeritus)
D. H. Putnam, Plant Sciences, UC Davis

Top of page

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2017 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

Accessibility   Contact webmaster.