Leptosphaerulina leaf spot
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.
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.
Last updated: 24.11.2021