Methods of preventing black spots on the leaves of orchids

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As the temperature rises, the prone period of black spot disease is coming again, so it is urgent to prevent the occurrence of black spot disease on the leaf surface of orchids.

Symptomatic form

The pathogen mainly infected orchid leaves, and the diseased leaves first appeared brown dots, which rapidly expanded into round and semicircular black-brown spots, surrounded by water-stained light yellow halos with a diameter of 1mm to 17mm. In the later stage, the central part of the disease gradually faded and became a dark brown spot with a light brown edge in the middle. There are light brown to gray-white blister protuberances on both sides of the susceptible site, and honey-yellow particles emerge in the humid environment, which is the conidia pile of the pathogen. The disease spot is easy to occur in the leaves of the middle and lower parts of the plant, the leaf tissue between the disease spots turns green and yellowing, and multiple disease spots can be linked into large patches, which can easily cause the leaf above the disease plaque to dry up or even the whole leaf to die.

Pathogen

Orchid black spot (Cylindrosporium phalaenopsidis) is caused by Dioscorea zingiberensis, which belongs to Dioscorea zingiberensis, which belongs to Dioscorea zingiberensis. The conidium disk of the pathogen was mainly born on the front of the leaf, initially buried under the epidermis, and then broke through and exposed, with a diameter of 129-257 μ m. The conidiophores are colorless, short, branched only at the base, with 2 separations, cylindrical, and spore-producing in the inner wall. Conidia colorless, thin-walled, linear, straight or slightly curved, 20.4-45 × 1.4-2.4 microns in size (figure 2). The optimum temperature for the growth and development of the pathogen is 20-25 ℃, but the spore germination rate can reach 50% at about 10 ℃.

Morbidity regularity

Orchid black spot pathogen overwinters in diseased tissue as hyphae or conidia. In Guangzhou, conidia began to invade and spread in the middle of December every year, and the epidemic period of the disease was from February to March of the following year. The disease was the most serious when there was continuous rain, fog and little sunshine. After May, when the temperature rose to 30 ℃, the disease subsided and stopped spreading. The pathogen can infect a variety of orchid plants such as Cymbidium, Phalaenopsis and Phalaenopsis. It can also harm Zhu Dinglan, hanging orchid and auspicious grass.

Prevention and cure method

1. Strengthen quarantine, pay special attention to quarantine of place of origin, select disease-free seedlings to control the spread of diseases.

two。 Remove the diseased and fallen leaves of orchids, cut off the disease spots in the upper and middle parts of orchid leaves in time, and burn them centrally.

3. Spray 1% Bordeaux twice before onset in early December, once every 10 to 15 days. During the onset period, you can choose 40% methomyl 600 times 700 times solution, or 45% Shibaoke 1000 times solution or 50% mancozeb 1000 times solution. When spraying, pay attention to spray evenly on both sides of the blade. The effect is better when fungicides are used alternately once every 10 days for many times.

Prevention and control

Choose a good orchid culture site. Choose a place with good ventilation and no pollution to make an orchid farm. It is best to have trees, pools and small water tanks around the orchid field to improve the air temperature. Shade shed with bamboo curtain, sunshade net on the top, its shade degree had better be automatically adjusted, sooner or later open and breathable. The orchid pots should be arranged sparsely and densely so that the air is well ventilated.

Keep the orchid farm clean and hygienic. Often clean up the dead leaves of orchids and weeds in pots. When bluegrass is divided into pots or new orchid seedlings are purchased, they should be disinfected and sterilized with methyl topiramate, and then planted after drying. Plant materials (humus, pond mud, charcoal, etc.) must be disinfected at high temperature or used after sun exposure to prevent bacteria from entering the orchid basin (field).

Cultivate strong orchid seedlings and enhance disease resistance. Fertilization and disinfestation must be carried out according to the plan. In the hibernating season of orchids, the leaves should be sprayed with methyl topiramate, carbendazim and chlorpromazine for more than 3 times, which can make the new seedlings thrive at the beginning of spring. After that, thiophanate methyl and carbendazim were sprayed every 20 days. Coupled with proper fertilization, bluegrass is strong and resistant to disease, so it is not easy to have black spot.

Master the season and prevent and cure in time. Black spot disease is very easy to occur in the rainy season every year, especially when it clears up after a long time of rain, it should be sprayed and prevented in time. In the germination stage of bluegrass in spring and autumn, the disease resistance of new seedlings is poor, so drug control should be strengthened.

Often observe orchid grass to prevent orchid disease. Often observe the growth of orchid seedlings, once found black spot leaves, cut off in time, focus on destruction. Clean up the surrounding environment and strengthen ventilation. In hot and humid weather, spraying carbendazim and thiophanate methyl 600 × 800 times, once every 15 days for 3 times in a row, can inhibit the occurrence of black spot.

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