Leptosphaerulina leaf spot in lucerne is caused by the fungal pathogen Leptosphaerulina trifolii. This disease mainly affects younger leaves, but also attacks the petioles and older leaves. Symptoms on the leaves vary with environment, the physiological stage of the leaf and the age of the plant. Dark-brown to black lesions 1-3 mm in diameter with a well-defined yellow (chlorotic) ring around them appear on the leaves and petioles. The centre of the lesion is usually paler (tan-colored). In the case of severe infection the lesions enlarge and merge, the leaves become yellow and fall off. Infection in spring can cause dwarfing. Damp conditions favour the disease.