Identification and Control Methods for Orchid Nematodes

Nematodes, also called roundworms, mostly live parasitically, and many of them also parasitize plant leaves, buds, flowers, roots and other parts. They prefer humid environments, often cause damage during hot and rainy seasons, and overwinter in the soil or on plants. Several dozen species of nematodes are known to harm ornamental flowers. For example, the dangerous nematode disease that harms Chinese orchids (Cymbidium) is caused by dagger nematodes; the root-knot nematode disease of Calanthe is caused by root-knot nematodes; and the yellow bud blight of Vanda is caused by Radopholus similis. These nematodes can all infect many plants.

When nematodes parasitize leaves, they cause yellow or brown patches on the leaves, leading to necrosis, withering, and even leaf drop, which makes the entire plant grow slowly and fail to develop properly. When they parasitize flower buds, the buds dry up or fail to form; when they parasitize roots, bead-like nodules or small galls appear on the roots, and the white round granular substances inside the galls are the bodies of female and male nematodes and their eggs. Ultimately this disease causes poor growth of the aboveground parts, smaller leaves, yellowing leaf color, fewer leaves, and a stunted, weakened plant, and in severe cases the whole plant dies.

To control nematodes, the first step is to eliminate the pathogen by pulling up and burning diseased plants. The soil should be drenched with a 1000-fold dilution of 40% omethoate. Soil can also be treated with 10% fosthiazate granules at 1.5-2 g/sq m, or aldicarb granules at 1.2-5.6 g/sq m.