Spring Black Stem in Alfalfa
Spring Black Stem
Symptoms
The disease, spring black stem, will produce small black spots on infected leaves, which turn yellow and fall off soon after infection. Spots are usually more severe on older leaves. Stem lesions are dark brown to black and may girdle the stem. Spring black stem can also attack crowns and roots, turning them black.
Cause
Phoma medicaginis, a soil fungus common in Kentucky alfalfa fields, is the causal agent for spring black stem. The fungus survives in the stubble from previous cuttings, and spreads easily by rainsplash, running water, and equipment. Leaf infections are most common during spring and early summer. This disease also attacks certain clovers.
IPM Techniques
- Timely, or even early, harvest can help prevent leaf loss.
- Cut alfalfa only when foliage is dry.
- Rotate away from forage legumes for at least two years.
- Some varieties may have partial resistance, but the reaction of most varieties to the disease is unknown.
References and Additional Information
- IPM-1 Kentucky IPM Manual for Alfalfa
- PPA-10d Kentucky Plant Disease Management Guide for Forage Legumes by P. Vincelli, Extension Plant Pathologist
- PPFS-AG-F-1 Summertime Foliar Diseases of Alfalfa by Paul Vincelli, Extension Plant Pathologist
- Compendium of Alfalfa Diseases. 2nd ed. Stuteville, D.L. & D.C. Erwin, (eds.) 1990.
