Control Methods for Edible Mushroom Diseases and Orchid Nematode Disease

The orchid nematode is a parasitic disease of plants in the Orchidaceae family. It belongs to the phylum Nematoda, class Nematoda, family Tylenchidae. In orchids, the adult nematode has a thread-like, elongated cylindrical body, tapering to fine points at both ends, without segmentation; the body consists of three germ layers and has a pseudocoelom. Nematode eggs are very small, the smallest being only 1 micron. Eggs that fall into the growing medium absorb water and swell when the medium is moist; after the larvae emerge, they invade the root velamen tissue, move upward along the plant into the leaves or mesophyll tissue or the storage tissue of the roots, where they absorb nutrients from the orchid plant, stimulate the cortical cells, and cause the formation of galls. After the adult nematode population matures, they mate and lay eggs within the galls; in winter the eggs hatch into larvae that remain inside the galls, and when spring returns the following year, the larvae overflow from the gall shells, are washed down by rain and irrigation into the growing medium, and repeat the infection.

In plants affected by this nematode disease, the nematodes begin migrating to the root velamen and leaves of the host in early summer, invading through stomata or hydathodes, causing pale yellow round spots to appear on the leaves, visible on both surfaces. After autumn, these yellow spots become thick, leathery scab-like galls, round in shape. The roots develop localized rough bending, then form flat, tumor-like small galls. When the roots degenerate and dry up in winter, the live galls remain in the growing medium or culture substrate. When the temperature rises to 18-22°C the following spring, the larvae inside the galls emerge and infect other roots and new individuals in the same pot. This repeats over and over. In orchids parasitized by nematodes, most leaves become thickened and hard, with scab-like growths, tillering is abnormal, and most fail to produce flower stems.

For the control of orchid nematode disease, prevention should be the main approach. The substrate can be rinsed with a 1% potassium permanganate solution, then washed clean with water and used after drying. When dividing pots in winter and spring, the leaves with galls should be cut off, and old roots, roots with galls, and dried bract leaves should also be cut off and burned. When round small yellow spots are found on the leaves, systemic insecticides such as aldicarb should be applied immediately; spray the leaf surfaces and undersides with 3% citric acid piperazine solution or 800-fold rotenone solution, or spray with 4% santonin aqueous solution; the above solutions can also be used to drench the growing medium so that the orchid roots can absorb them.