Leptosphaerulina leaf spot

Leptosphaerulina trifolii


Lepto leaf spot disease of alfalfa is caused by the fungus Leptosphaerulina trifolii. The disease can be recognized by the typical yellow and brown spots. However, since other fungi cause similar symptoms, the final diagnosis can only be made by microscopy.

Damage symptoms

Symptoms include spots on leaves and petioles that start as small reddish-brown to black so-called pepper spots. These can enlarge, are oval to roundish and about 1 to 3 mm in diameter. They have light brown to brown centers and a darker brown border. These "eyespots" are often surrounded by a lighter colored halo. Under optimal conditions for disease development, large light brown spots appear. These spots merge and then appear as large pale patches. Such affected leaves die. Dead leaves and their stems remain on the plants for a while, but are sometimes shed. Emerging young leaves also show symptoms, but usually do not die. In addition to leaf drop, infections can also cause plants to become stunted.

Symptoms of lepto leaf spot disease depend on the age of the plants, their growth stage, and environmental conditions, especially light intensity. Young leaves are often very severely affected. Older leaves, petioles and stems are infected only in succession.

Host plants

The host plants of lepto leaf spot disease are alfalfa, clover and other legumes, grasses, potato, corn, taro (in Asia), and many others.


Lepto leaf spot disease is widespread worldwide. The pathogen follows the distribution of its host plants.

Propagation and transmission

The disease typically occurs in late spring and early summer on alfalfa. The fungus survives on infested plant debris in the soil or lives saprophytically in the soil. Spore germination occurs at high humidity or dew coating on leaves. An optimum temperature of 20 °C and humid conditions promote disease development.

Economic importance

Once lepto leaf spot disease of alfalfa is established in a stand, crop losses can occur, especially if harvest is delayed or delayed.

Prevention and control

  • To prevent lepto leaf spot disease, harvest as early as possible.
  • In the USA, less susceptible varieties are named, e.g. Agate and Ramsey.

Last updated: 24.11.2021

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