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Lepto Leaf Spot: Kentucky Alfalfa IPM

Lepto Leaf Spot


Symptoms

Plants with Lepto leaf spot will have tan leaf spots with brown borders, giving an "eyespot" appearance. Spots sometimes have a yellow margin. Leaves and stems eventually blight and turn tan. Spots may be evident in all but the very youngest leaves on growing shoots. This disease tends to be most severe in first or second cuttings.

Cause

The fungus Leptosphaerulina trifolii is the causal agent of Lepto leaf spot. Development of the disease is favored by cool, wet weather during alfalfa regrowth. Disease pressure is often high following freezing of alfalfa stems or in fields where a cutting is left unharvested. This is because dead alfalfa leaves and stems are often colonized by the fungus, which then produces spores that are spread to the healthy alfalfa. The fungus survives in alfalfa residue. Spores are spread by air currents and can also attack clovers.

IPM Techniques

  • Timely (or early if necessary) harvest can help prevent leaf loss and accumulation of spores in the field.

  • Some varieties may suffer less yield loss, but the reaction of most varieties to the disease is unknown.

  • Rotate away from forage legumes for at least two years.

References and Additional Information

  • IPM-1 Kentucky IPM Manual for Alfalfa

  • PPA-10d Kentucky Plant Disease Management Guide for Forage Legumes, P. Vincelli, Extension Plant Pathology, University of Kentucky

  • ID-104 Managing Diseases of Alfalfa, P. Vincelli, Extension Plant Pathology, and G.D. Lacefield and J.C. Henning, Agronomy, University of Kentucky

  • Compendium of Alfalfa Diseases. 2nd ed. Stuteville, D.L. & D.C. Erwin, (eds.) 1990.