A Detailed Guide to Treating and Preventing Stem Rot in Orchids

Orchids are delicate. Growing orchid plants requires not only controlling various environmental variables, such as light and water, but also fertilizing reasonably and guarding against the threat of pests and diseases. Orchid stem rot is a common disease of orchids and often occurs together with orchid root rot. Dealing with these diseases requires us to take appropriate measures.

Treatment Techniques and Prevention Methods for Orchid Stem Rot

I. Treatment Techniques

1. Pull out the entire pot of orchids, wash them clean, cut away the diseased plants together with the already infected orchid plants, and use a blade to completely remove the rotted pseudobulbs;

2. Soak the healthy parts retained after pruning in a slightly stronger fungicide solution (difenoconazole) for no less than 1 hour;

3. Dry them, then mix metalaxyl and mancozeb into a paste, seal the pseudobulb areas of the orchids, and dry again;

4. Wrap the pseudobulb areas with sterilized sphagnum moss, and replant in a new pot with new soil;

5. After planting, do not water, do not expose to sunlight, and place in a ventilated spot;

6. After 3 days, soak thoroughly with clean water, place in a ventilated and airy spot, and manage according to usual methods (be careful to fertilize sparingly);

7. Each month, soak the orchid pot again with a fungicide solution (slightly diluted), and the orchid plants can gradually recover their vigor.

II. Prevention Methods

1. During the growing process, the orchid-growing environment should be kept clean and well ventilated; before potting, the orchids, orchid pots and growing medium must be disinfected, and the growing medium must drain well; avoid wounds on the orchid plants, and in particular prevent insect bites in the soil from injuring the pseudobulbs and causing infection, so insecticides can be applied to the soil; in production, diseased seedlings and the growing materials and pots they used should be discarded and destroyed in a centralized manner.

2. If measures are taken promptly in the early stage of plant infection and the diseased spots are excised, the plant can still be retained, but because of the reduction in leaf area, flowering will inevitably be affected; if it is not discovered in time and the best period for prevention and control is missed, and given that the disease develops very rapidly, the possibility of curing the diseased plant is extremely low.

3. Fungicides can be used for prevention and control, such as 72% agricultural streptomycin sulfate soluble powder at 800 times dilution, 77% copper hydroxide wettable powder at 1000 times dilution for whole-plant spraying (including leaf undersides, leaf surfaces and the crown); 45% prochloraz emulsifiable concentrate at 1500 times + tetracycline powder at 2000 times + 50% dimethomorph wettable powder at 2000 times, for whole-plant spraying (including leaf undersides, leaf surfaces and the crown); Antaisheng at 500 times + prochloraz at 1500 times + streptomycin sulfate at 500 times, for whole-plant spraying (including leaf undersides, leaf surfaces and the crown); research reports that 80% ethylicin emulsifiable concentrate, 20% bismerthiazol wettable powder, and Lifukang 50% chloroisobromine cyanuric acid soluble powder also have good antibacterial effects.

What Is Orchid Stem Rot

Stem rot is also called fusarium wilt and wilt disease. The cause is Fusarium oxysporum of the Deuteromycotina and Erwinia carotovora. The two bacteria live symbiotically, mutate into second-generation mycelium, and also because of the symbiosis with soft rot bacteria. It is an orchid disease with a high incidence rate and severe losses in recent years. The peak of onset is from May to September each year, and the earliest cases can appear in February; high-temperature and high-humidity environments are more conducive to the rapid development of the disease.

Symptoms of Orchid Stem Rot

The typical symptom of onset is that old pseudobulbs begin to turn yellow and wither. The core leaf of an old pseudobulb starts to yellow from the base, then rapidly spreads from bottom to top and from inside to outside. One old pseudobulb yellows and dries to death within 1-2 days. If touched by hand, the entire pseudobulb will break off at the ring of the leaf base. Inexperienced orchid growers often think it is just the old pseudobulbs fading; but by the time the disease continues to develop and more vigorous pseudobulbs collapse, it is often already incurable.

Several Common Orchid Diseases

1. Rot disease. Caused by pathogenic molds, and generally affecting the leaf bases, seedlings and roots. The causes are broken roots when digging up orchid plants, damage during transport, Pythium in the growing soil, excessive base fertilizer during cultivation, watering with human feces and urine, and salt in the water quality. In mild cases, orchid roots rot and leaves turn red; in severe cases, seedlings wither, flower spikes shrivel, and eventually the plant dies.

2. Black spot disease. Black spots appear on the leaf surface and gradually expand. In severe cases, they spread locally to the entire tissue, causing most of the leaves to wither and turn black, losing the ornamental value of the leaf form and causing poor orchid growth.

3. White silk disease. A disease caused by pathogens, mostly occurring during the rainy period at the turn of summer and autumn. At the base of the leaf sheath and beside the pseudobulbs, a layer of white silky mycelium spreads, and it can cause orchid plants to die very quickly.

4. Brown rot. A bacterial disease. It mainly occurs on new leaves and pseudobulbs. In the early stage of onset, water-soaked spots first appear on the leaves and pseudobulbs, then turn light brown and gradually dark brown, and the surface of the affected area becomes wrinkled; water-soaked halos appear around it.

5. Anthracnose. It is the most serious disease in Cymbidium sinense and Cymbidium ensifolium, initially appearing as small yellow spots that gradually spread into dark brown round spots.

When orchid stem rot occurs, it appears as old leaves yellowing and withering. This symptom is easily overlooked and mistaken for the normal metabolic phenomenon of orchid plants, so fellow orchid growers must identify it carefully. In addition, the editor has also summarized here some other orchid diseases and their symptoms at onset, which have certain reference value for orchid management.