Persistent Rain Leaves Fields Damp, Raising Risk of Onion and Garlic Diseases, Taiwan Farm Agency Warns

Sunshine has returned to southern Taiwan, but the fields remain wet enough to put onion and garlic crops at risk. The Southern Regional Agricultural Research and Extension Station urged farmers to strengthen disease prevention after a period of persistent rain.

The damp conditions can promote purple blotch, black rot and anthracnose. Scallions have also shown signs of a leaf-curling form of anthracnose, which can cause leaves to curl, turn yellow and wilt, while also leading to stem rot. The agency called for close monitoring, particularly as the next garlic planting season approaches.

Purple blotch first appears as small, pale-brown spots. These can expand into sunken, dark-purple spindle-shaped lesions with pale-red to pale-purple edges and black mold-like rings. Its spores can spread through the air, while the fungus can survive in crop residue and enter plant tissue during rain or prolonged dew.

Black rot initially produces white to yellow-brown spots on leaves. Later, the leaf tips turn yellow and dry out, a symptom commonly known as “dry tail,” with black mold-like growth visible on affected areas. Anthracnose begins with pale spots, which gradually enlarge into black, ring-shaped lesions and can cause leaves to dry or plants to wilt.

The station recommended applying registered pesticides as soon as disease appears. Farmers should use products approved for small-leaf and root-and-stem vegetables in the onion family, follow dilution instructions and rotate different pesticides to reduce the risk of resistance. Registered treatments for scallion anthracnose can also be used against the leaf-curling form of the disease.