Symptom identification of leek diseases is the first step in control

Leeks are prone to diseases in fields where they are grown in continuous cropping for many years. The common ones include gray mold, late blight, rust and root rot, which mainly damage the leaves and false stems. In mild cases the leaf tips turn yellow and dry up; in severe cases whole patches rot away, affecting the number of harvests and the quality. Learning to read the symptoms is the first step in control.

Gray mold mostly occurs under low-temperature, high-humidity conditions, and is especially common in greenhouse cultivation in winter and spring. In the early stage of the disease, water-soaked pale spots appear at the leaf tips or leaf margins, then expand into grayish-white lesions. When humidity is high, a layer of gray mold grows on the diseased parts, and the leaves gradually turn yellow and soft-rot from the tip downward.

Late blight, on the other hand, favors hot, rainy weather, and can affect the leaves, false stems and roots. The diseased parts first appear dark green and water-soaked, after which the tissue softens and droops, looking as if it has been scalded with boiling water. In damp weather sparse white mold can be seen on the surface, and in severe cases the whole plant rots and lodges.

Rust and root rot each have their own characteristics. Rust forms small orange-yellow to dark brown blister-like spots on the leaf surface; later the leaves are covered with rust powder and turn yellow and dry. Root rot shows up as roots turning brown and rotting, with a reduced ability to take up water and nutrients; the aboveground part grows thin and weak, the leaves turn yellow, and the growth gets worse year after year.

During routine field walks, focus on observing the leaf tips, leaf margins and the base of the false stems, and then combine this with the season of onset to judge the type of disease. Diseased leaves should be taken out of the field promptly for disposal, and attention should be paid to ventilation and reducing humidity, as well as reasonable fertilization and watering. Avoid applying too much nitrogen fertilizer; keep the plants sturdy and there will naturally be fewer diseases.