Symptom Identification and Control Methods of Garlic Leaf Blight

Leaf blight is a major disease of green garlic and, in severe cases, causes the entire leaf to die off, affecting yield.

I. Symptom identification This disease mainly damages leaves and flower stalks. When leaves are infected, it usually starts from the leaf tip and gradually develops toward the leaf base, spreading from the bottom upward. At first, pale white small round spots appear, which later expand into oval or irregular grayish-white or grayish-brown lesions, and black mold-like growth develops on the diseased parts; in severe cases, the entire leaf dies off. When flower stalks are infected, they tend to break at the diseased part, and finally many small black grains are scattered on the lesions. Key identification points: black mold-like growth or small black grains develop on the diseased parts of leaves and flower stalks, and in severe cases the diseased leaves die off.

II. Disease development pattern

1. Pathogen Garlic leaf blight is caused by infection by Pleospora herbarum (Pyrenophora excelsa) of the Ascomycota. The conidiophores emerge from the stomata and are slightly curved; conidia are borne singly, oval or elliptical, gray or dark yellowish-brown. The perithecia are spherical and contain 20-30 asci; the asci are generally elongated-elliptical and contain 8 ascospores each, and the ascospores are yellowish-brown.

2. Infection cycle The pathogen mainly overwinters in the soil as perithecia with diseased residues. When environmental conditions are suitable the following year, ascospores are released to cause primary infection. After disease onset, conidia are produced on the diseased parts for spread and secondary infection.