What are the main diseases of orchids? Detailed explanation of key control measures

Growing Techniques Jan 1, 1970 0 views

I. Orchid anthracnose is an important disease of orchids. In the early stage of the disease, circular, dark brown spots appear on the leaves, which then gradually expand with dark brown edges and grayish-white centers, and the spots easily crumble. When severe, the spots are numerous and the leaves turn yellow and wither.Control measures:(1) Cut off diseased leaves, remove diseased residues, and burn them in a centralized manner;(2) Pay attention to ventilation and light transmission;(3) Cultivate robust plants to reduce disease incidence, prevent excessive watering, and especially avoid directly spraying water onto the plants;(4) For diseased plants, spray with 50% benomyl or 70% thiophanate-methyl or 50% carbendazim at 600-800 times dilution, about once every 10 days, for 3-4 consecutive sprays, with fairly good control effect.

II. Orchid round spot disease, also known as leaf blight. The pathogen infects the leaves, initially as small reddish-brown spots, which rapidly expand into semicircular or circular dark brown spots. When there are many spots on a leaf, the leaf tissue between the spots loses its green color, turns yellow and dies.Control measures:(1) Remove diseased leaves.(2) During the plant growing season, spray with 1:1:100 Bordeaux mixture, 70% chlorothalonil at 500 times dilution, 50% thiram at 800 times dilution or 65% zineb at 500 times dilution for control.III. Orchid southern blight is a fungal disease. At first, the base of the orchid leaves near the soil turns brown and rots, and soon white silky mycelium is produced, spreading over the soil surface around the roots, and finally causing the entire leaf cluster to die. It mostly occurs in hot and rainy seasons.Control measures:(1) Remove diseased plants;(2) Pay attention to ventilation;(3) Disinfect with pentachloronitrobenzene at 0.2% of the pot soil weight, mix thoroughly and evenly before planting;(4) For diseased plants, mix 50 g of pentachloronitrobenzene powder with 3-5 kg of semi-dry, semi-moist fine soil, and spread the medicated soil around the root crown of the plant.IV. Orchid ringspot virus can infect Cymbidium ensifolium, producing mosaic symptoms; and green ringspots.Control measures:(1) Remove diseased plants, do not use diseased plants to propagate new plants, and in diseased areas, efforts should be made to cultivate disease-free seedlings;(2) During orchid management (division propagation or repotting, etc.), try to minimize damage to leaves to prevent sap friction transmission.V. Orchid necrotic spot disease is a viral disease. The virus is transmitted through sap, green peach aphids and other routes. On Cymbidium ensifolium, it produces chlorotic spots and necrotic spots; on Cattleya, it produces local necrotic spots; on Epidendrum, it produces mosaic symptoms;Control measures:(1) Using seed propagation can avoid virus transmission;(2) Reasonable fertilization to promote robust plant growth can reduce disease severity;(3) Spray plants with insecticides to kill aphids: 40% dimethoate at 1000 times dilution, 50% malathion at 800 times dilution, 75% phoxim at 1000 times dilution.VI. Orchid shoot rot is a bacterial disease. It mainly occurs on tiller buds, initially as water-soaked spots the size of mung beans at the base of the buds, which then become dark green scald-like large patches, extending to the outside of the bud sheath, showing dark brown rot, and diseased leaves are easily pulled out.Control measures:(1) Control soil moisture content; for diseased potted flowers, stop watering, and only water after the disease is controlled;(2) When new shoots emerge 4-5 cm, spraying with 0.01% boric acid solution or 1000 times dilution of dithianon or phenazine oxide has a certain effect, and streptomycin can also be used for control.VII. Orchid leaf sclerotinia disease first shows light brown water-soaked rot at the leaf base, then extends to the whole leaf, turning reddish-brown, causing orchid leaves to wither into tubes. For control, pull out diseased plants and refer to the control of southern blight.VIII. Orchid viral disease forms brown circular or oblong necrotic spots on leaves, which then expand into large patches, and the leaves easily turn yellow and wither. For control, burning diseased plants is mostly adopted.

Key points of spring management techniques for orchid cultivation

After the beginning of spring, the climate changes greatly, with many overcast and rainy days, and cold waves often occur, which is very unfavorable for orchid growth. At this time, if management cannot keep up, it is very easy to cause orchid root rot, bud rot, and even death of the entire plant.

Heat preservation and waterlogging prevention: In spring, Cymbidium sinense and Cymbidium goeringii in full bloom must be kept indoors to protect the flower scapes and flowers, because overcast, rainy and cold weather will shorten the flowering period, and if exposed to cold rain, the flowers will rot. For Cymbidium ensifolium, Cymbidium kanran, etc. in the budding stage, they can be placed outdoors, but attention must be paid to drainage and waterlogging prevention in the orchid pots, and it is best to set up plastic film above the orchid pots to shelter from rain. During this period, all fertilizers must be avoided for orchids, and the pot soil should be kept slightly moist; otherwise, the new shoots of Cymbidium ensifolium and Cymbidium kanran will rot to death, with the shoot tips rotting and turning dark brown, extending all the way until the entire shoot withers and dies, commonly known as "black death." Dead spring shoots will seriously affect the growth, propagation and flowering of the entire pot of orchids that year.

Prevention and control of diseases and pests: Continuous rainy weather in spring is a period of frequent occurrence of various diseases and pests. High-humidity environmental conditions will lead to the occurrence and aggravation of orchid brown spot disease, and will also cause damage by snails, aphids, cutworms, mole crickets and other pests. For brown spot disease, spray 50% carbendazim or 70% thiophanate-methyl at 800-1000 times dilution at the initial occurrence, for 2-3 consecutive sprays, with an interval of 7-10 days. For pests, manual capture is the main method, keep the orchid pots and surroundings clean, and scatter quicklime to prevent pests from entering the pots through the pot walls and drainage holes at the bottom to cause damage.

Timely fertilization: For Cymbidium sinense and Cymbidium goeringii that have finished flowering, fertilizer should be supplemented in time, preferably by applying thin horse hoof piece water and spraying the leaves with 0.1% potassium dihydrogen phosphate solution, to promote spring growth. May is the fertilization period for all orchids, and 50 g to 100 g of slow-release organic fertilizer granules and bone meal can be buried along the edge of the orchid pot. Spray bud-strengthening fertilizer every week, with the fertilizer solution being 0.1% potassium dihydrogen phosphate; to prevent diseases, thiophanate-methyl or carbendazim can be added for mixed spraying.

Common flower diseases and control methods

1. Damping-off

Main flowers affected: China aster, China pink, lily, gladiolus, begonia, iris, cockscomb.

Main symptoms: Elliptical dark brown lesions appear at the base of the seedling stem, the lesions gradually sink, and after expansion encircle the stem, finally shrinking, drying up and causing death.

2. Seedling blight

Main flowers affected: Calceolaria, gloxinia, begonia.

Main symptoms: Water-soaked lesions appear at the base of the seedling stem, then turn yellowish-brown, constrict and sink into a thread-like shape, and soon the seedling topples.

3. Root rot

Main flowers affected: Gladiolus, cornflower, China pink, lily, jasmine, poinsettia, begonia, camellia, tulip.

Main symptoms: Damages roots and bulbs, etc. The affected parts rot brown, and in severe cases die in patches.

Control key points for diseases (1-3): (1) Soil disinfection, use sterile new soil or steam the soil in a pot for 1 hour or disinfect with formalin solution; (2) Watering should be "see dry, see wet," avoiding waterlogging; (3) In the early stage of disease, irrigate the root zone with 50% amobam at 300-500 times dilution, using 2-4 kg of solution per square meter.

4. Powdery mildew

Main flowers affected: Chinese rose, rose, rugosa rose, tree peony, Chinese peony, chrysanthemum, dahlia, cineraria, garden balsam.
Main symptoms: Damages young leaves, young buds, young shoots and flower buds, etc. After onset, a layer of white powdery substance grows on the affected parts, causing leaves to curl, young shoots to bend, flowers unable to open, and in severe cases leaves wither and die.

5. Anthracnose

Main flowers affected: Orchid, clivia, Michelia alba, magnolia, camellia, fig, Aglaia odorata, tree peony, plum blossom, rubber tree, cactus, rose.

Main symptoms: Damages leaves and stems. After infection, grayish-brown or dark brown spots appear on the leaves, then expand into nearly circular concentric rings, with small black dots on them, often arranged in circles, causing leaves to wither and fall off.

6. Black spot

Main flowers affected: Chinese rose, rose, rugosa rose, plum blossom, Elaeagnus-leaf elm, yellow rose, peach blossom.

Main symptoms: Black or brown nearly circular spots or irregular concentric ring spots appear on the leaves, causing premature leaf drop.

7. Brown spot

Main flowers affected: Tree peony, Chinese peony, chrysanthemum, daisy, Elaeagnus-leaf elm, Chaenomeles speciosa.

Main symptoms: Brown or dark brown circular spots appear on the leaves, then the leaves gradually turn black and die.

8. Gray mold

Main flowers affected: Wax begonia, fairy primrose, dahlia, begonia, fuchsia, Calceolaria, gloxinia, cineraria, cyclamen, China aster.

Main symptoms: Damages leaves, stems, flowers and fruits. Water-soaked spots first appear on the affected parts, then turn brown or dark brown and rot; under humid conditions, gray fuzzy mold grows.

Control key points for diseases (4-8): (1) In late autumn or early spring, remove dead branches and fallen leaves, and promptly prune diseased branches and leaves and destroy them; (2) Spray zineb at 600 times dilution before disease onset for protection; (3) Fertilize and water reasonably, and pay attention to ventilation and light transmission; (4) In the early stage of disease, spray 50% carbendazim or 50% thiophanate-methyl at 500-800 times dilution or 75% chlorothalonil at 600-800 times dilution; (5) To control gray mold, 70% pentachloronitrobenzene and 80% zineb powder can also be mixed in equal amounts evenly, using 8-10 g per square meter.

9. Southern blight

Main flowers affected: Tree peony, Chinese peony, orchid, iris, garden balsam. Main symptoms: White silky mycelial mats appear at the stem base, then brown rapeseed-shaped sclerotia grow on them, and the diseased plant dies.

10. Sclerotinia rot

Main flowers affected: African daisy, cornflower, tulip, citrus.

Main symptoms: At root cut surfaces or wounds, a white mycelial layer covers the area, the root bark rots and turns brown, and black rat-dropping-shaped sclerotia are produced.

Control key points for diseases (9-10): (1) Use formalin or pentachloronitrobenzene for soil disinfection; (2) Select disease-free seedlings or soak in 70% thiophanate-methyl at 500 times dilution for 10 minutes before planting; (3) Practice crop rotation and avoid continuous cropping; (4) Water reasonably and drain promptly after rain.

11. Seedling stem rot

Main flowers affected: Japanese maple, Japanese false cypress, hinoki cypress, boxwood, Oriental arborvitae, golden larch, Japanese cedar.

Main symptoms: The stem base rots in a spongy manner, with black sclerotia growing on it, causing the root cortex to rot.

Control key points for disease (11): (1) Water promptly during high temperature and drought, and pay attention to shading; (2) Apply appropriately more phosphorus and potassium fertilizers; (3) In the early stage of disease, promptly spray carbendazim or thiram at 800 times dilution.

12. Sooty mold

Main flowers affected: Calla lily, Rohdea japonica, croton, azalea, camellia, oleander, boxwood, osmanthus, crape myrtle, Pittosporum tobira, lily, Michelia alba, rubber tree, citrus.

Main symptoms: On young branches, leaves and fruits, a black mold layer forms, hindering photosynthesis and affecting plant growth and ornamental value.

Control key points for disease (12): (1) Pay attention to ventilation and light transmission, and appropriately reduce indoor humidity; (2) In the early stage of disease, when there are few mold spots, gently wipe the mold layer clean with clean water. When the disease is more severe, spray 50% carbendazim at 500-800 times dilution.

13. Gray plaster disease

Main flowers affected: Red-leaf plum, plum blossom, cherry blossom, osmanthus, privet.

Main symptoms: Circular or irregular fungal films form on branches and trunks, appearing plaster-like, with the center of the affected part dark gray, the outer layer dark brown, and the edge grayish-white, often sunken.

Control key points for disease (13): (1) In winter, scrape off the fungal film with a bamboo strip or small knife, and apply 3-5 degrees Baumé lime-sulfur mixture; (2) Prune promptly to allow ventilation and light transmission; (3) Spray pesticides at the appropriate time to control scale insects.

14. Snapdragon blight

Main flowers affected: Snapdragon, periwinkle, lily, cactus, cockscomb, scarlet sage, carnation, loquat.

Main symptoms: Infects roots and stems. Root infection causes root rot; stem infection causes the affected part to turn brown and constrict, ultimately causing stems and leaves to wither and die.

15. Peony blight

Main flowers affected: Tree peony, Chinese peony, lily, cactus, carnation.

Main symptoms: Mainly infects leaves, petioles and stems. On leaves, oil-soaked small spots appear, then become irregular, with gray centers; in later stages, diseased leaves wilt, wither and droop.

Control key points for diseases (14-15): (1) Use crop rotation or use new culture soil; (2) Choose loose, fertile, well-drained locations for planting, avoiding water accumulation; (3) Promptly pull out diseased plants and destroy them; (4) Spray zineb 3-4 times before disease onset to prevent occurrence.

16. Citrus scab

Main flowers affected: Kumquat, bitter orange, citrus.

Main symptoms: Infects leaves, stems and fruits. On leaves, scab-like grayish-brown spots appear, and the leaves become deformed; after fruit infection, brown spots are produced, causing young fruits to drop early.

Control key points for disease (16): (1) Combined with pruning, cut off diseased shoots; (2) Fertilize reasonably, do not apply excessive nitrogen fertilizer, and increase phosphorus and potassium fertilizers; (3) Spray zineb at 600 times dilution.

17. Rose stem blight

Main flowers affected: Rose, Chinese rose.

Main symptoms: Mainly infects stems. In the early stage of disease, reddish-purple circular spots appear, then the center of the spots becomes grayish-brown and the edges dark brown; in later stages, dark brown cracks appear on the epidermis of the affected parts.

18. Peony stem blight

Main flowers affected: Tree peony, Chinese peony

Main symptoms: In the early stage, small brown spots appear on the surface of young branches, then the spots increase, the affected branches turn brown, and in late autumn dense dark brown small granules grow on the affected parts.

Control key points for diseases (17-18): (1) Combined with winter pruning, cut off diseased branches and burn them; (2) Avoid causing wounds; (3) Before disease onset, spray 600 times dilution zineb solution once every 7-10 days, for 3-4 consecutive sprays.

19. Bacterial soft rot

Main flowers affected: Iris, gladiolus, cyclamen, calla lily, hyacinth, lily, dahlia, wallflower.

Main symptoms: Mostly occurs on rhizomes, corms, bulbs and tuberous roots. The affected parts mostly show brown, sticky, slippery soft rot and emit a foul odor.

Control key points for disease (19): (1) Practice crop rotation and select disease-free propagation materials; (2) Promptly control underground pests; (3) In the early stage of disease, irrigate the root zone soil with fenaminosulf at 500-1000 times dilution; (4) The storage site should be disinfected with 80 times dilution formalin solution, and attention should be paid to ventilation.

20. Crown gall

Main flowers affected: Plum blossom, fig, cherry blossom, grape, chrysanthemum, Chinese rose, lilac, crape myrtle, geranium.

Main symptoms: Mainly damages the root crown. After infection, tumors of varying sizes form, and in severe cases the entire plant dies.
Control key points for disease (20): Practice crop rotation or treat the soil with pentachloronitrobenzene, using 6-8 g of 70% powder mixed with 0.5 kg of fine soil per square meter.

21. Bacterial shot hole

Main flowers affected: Plum blossom, cherry blossom, peach, apricot.

Main symptoms: Damages leaves, young shoots and young fruits. After leaf infection, brown water-soaked lesions appear, surrounded by light yellow halos; in later stages, the lesions become dark brown or purple-brown, the edges become lignified, forming shot holes.

Control key points for disease (21): (1) Promptly prune affected parts and destroy them; (2) In the early stage of disease, spray zineb at 500-600 times dilution.

22. Algal leaf spot

Main flowers affected: Camellia, osmanthus, Michelia figo, white magnolia, magnolia, hibiscus, holly, phoenix tree, citrus.

Main symptoms: Radiating grayish-green or greenish-brown spots appear on the leaves, with fine striped felt-like material on the surface of the spots, and the edges are irregular.

Control key points for disease (22): (1) Pay attention to ventilation and light transmission; (2) Fertilize and water reasonably; (3) Promptly remove diseased and residual plants and burn them; (4) In the early stage of disease, spray 50% thiophanate-methyl at 500 times dilution.

23. Nematode disease

Main flowers affected: Cyclamen, snapdragon, dahlia, chrysanthemum, garden balsam, scarlet sage, iris, geranium, holly, begonia, rose.

Main symptoms: Most species damage the roots, forming tumors or root galls; in severe cases, the fine roots turn brown and rot, and the leaves wither.

Key control points for disease (23): 1) Use new soil or sterilized soil for potted plants; 2) Practice crop rotation in garden planting and avoid continuous cropping; 3) Hot water treatment: soak the diseased parts used for propagation in hot water at 50°C for 10 minutes or 55°C for 5 minutes.

24. Viral disease

Main ornamental flowers damaged: narcissus, orchid, lily, chrysanthemum, dahlia, peony, carnation, China aster, gladiolus.
Main symptoms: The common symptoms are mosaic and yellowing; stunting, bushy growth, crinkling, and leaf curling are also relatively common.

Key control points for disease (24): 1) Select excellent varieties with disease tolerance and resistance; 2) Strictly select virus-free planting material; 3) Use shoot-tip culture for virus elimination and tissue culture to propagate virus-free plantlets; 4) Spray insecticides such as dimethoate at the appropriate time to eliminate virus-transmitting insects such as aphids, leafhoppers, and whiteflies; 5) Promptly pull out and destroy diseased plants;

25. Chlorosis

Main ornamental flowers damaged: camellia, azalea, orchid, banana shrub, white champaca, gardenia.

Main symptoms: In the early stage, chlorotic spots appear on the leaves, and later the leaves all turn yellow-white.

Key control points for disease (25): 1) Use acidic soil when planting; 2) It is best to use rainwater or snow water for watering flowers; 3) During the growth period, spray the leaves once every 10-15 days with 0.2% ferrous sulfate solution or apply alum fertilizer water once.