What are the control methods for nematode disease in orchids?

Orchidnematode Anguina orchidii, whose English name is Nematode, is a parasitic disease of orchids (Orchidaceae). This worm belongs to the phylum Nematoda, formerly called Nemathelminthes, class Nematoda, family Tylenchidae.Orchidnematodes are the pathogenic parasites oforchidnematode disease. The adult body is thread-like, long and cylindrical, tapering and slender at both ends, unsegmented, composed of three germ layers, with a pseudocoelom. The digestive tract is not curved; the front end is the rostrum, and 0.5 mm below it there is a ringed band about 10 micrometers long, while the rear end is the cloacal opening. The female is 5 mm long, the male 2.5 mm long, with two copulatory spicules at the tail. Nematode eggs are very small, with a diameter below 0.2 mm, the smallest only 1 micrometer. Galls that fall into the growing medium swell by absorbing water when the medium is moist; after the larvae spill out, they invade the root velamen tissue, move upward along the plant into the leaves or mesophyll tissue or the storage tissue of the roots, absorb nutrients from the orchid plant, stimulate the cortical cells, and cause the formation of galls. After the adult nematode population matures, it mates and lays eggs inside the galls; when winter comes, the eggs hatch into larvae, which remain in the galls, and when spring returns the following year, the larvae spill out of the gall shells, are washed by rainwater and irrigation into the growing medium, and repeat the infection. In plants with this disease, the worms 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 scabby galls, round in shape. Other parts of the leaves without galls show no lesions and grow normally. The roots show 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 in the galls spill out and infect other roots and new individuals in the same pot. In orchid plants parasitized by nematodes, most leaves become thick and hard, with scab-like growths, tillering is abnormal, and most cannot send up flower stems. For the control of orchid nematode disease, the principle of "prevention is more important than cure" should be followed. First, strengthen the disinfection of the growing medium; it can be rinsed with 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 as well as roots with galls and dried bract leaves should be cut off and burned. Second, when round small yellow spots are found on the leaves in early spring, systemic insecticides such as aldicarb should be applied immediately; spray the leaf surfaces and undersides with 3 percent citrazinic acid piperazine solution or 800-fold rotenone solution, or spray with 4% santonin (Satolen) aqueous solution; the above solutions can also be poured onto the growing medium so that the orchid roots absorb them. In this way, the nematodes parasitic within the tissues can be killed within two days, and the plant can be expected to recover and not form galls. Third, if engaged in export or large-scale domestic sales, in order to ensure that the plants do not carry nematode disease, disinfestation treatment can be carried out before packing and transport. The process has three steps: first, wash the roots and leaves of the orchid plant clean with water; second, soak them in 1% hydrogen peroxide solution or 1% potassium permanganate solution for 60 seconds, then dry them; third, soak them in 800-fold derris extract solution for 15 minutes, take them out and dry them, and they can then be boxed. If there are worms, they will all have been killed. The above points are my understanding of nematode disease, for reference by the broad community of orchid lovers and traders. Shen Dezu