Phalaenopsis Cultivation: Phalaenopsis Orchids are very sensitive plants for their successful cultivation grower have to pay keen attention to every aspect of its growth factor. In this, we discuss usual problems in phalaenopsis cultivation encountered by the grower.
Aphids: Both the nymphs and adults suck sap from the tender parts of the plant and also acts as a vector of diseases. Buds and flowers may fail to open and leaves may have a sticky deposit. The honeydew secreted by aphids is very attractive to ants and is an ideal medium for sooty mould growth.
Wash aphids away with a jet of water from the plants. Application of entomopathogenic fungi like Beauveria bassiana, Paecilomyces fumosoroseus, Verticillium lecanii @ 2m//L of water. Plants should be treated with Imidacloprid 17.8 SL 0.3ml/lit, at 10 days intervals.
Soft brown scales and biosduval scales are found attacking Phalaenopsis orchids. Brown scales are oval and lumpy while the biosduval scales are a white cottony mass in appearance.
They attach to and suck the sap from the leaf underside, leaf axils, etc. Severe infestations cause chlorotic areas to appear on the leaves and plant surfaces which turn yellow, darken and cause the leaf to drop prematurely. Sometimes brown scales are found feeding on the flowers.
Remove old leaf and flower sheaths to remove scale hiding places. Mechanical removal of these scales with 70% isopropyl alcohol (rubbing alcohol) is recommended. Microbial biopesticides like Beauveria bassiana, Metarhizium anisopliae, Verticillium lecanii @ 2ml/L of water can be applied. In severe conditions spray with Acephate 75 SP 1g/L and Imidacloprid 17.5 SL 1 ml/L at 15 days intervals.
These are sucking insects that can attack any plant part but are generally found hiding at the leaf and stem junction. Severe infestations cause chlorosis of infected areas and premature leaf drop. Remove old leaf and flower sheaths to remove hiding places and allow easy monitoring.
Microbial biopesticides like Beauveria bassiana, Metarhizium anisopliae, Verticillium lecanii @ 2ml/L of water can be applied. In severe conditions spray with Acephate 75 SP 1g/L and Imidacloprid 17.5 SL 1 ml/L at 15 days intervals.
Red spider mites lacerate and suck sap from the leaf under surface and may have webbings and brown splotches from the mite excrements. The upper leaf surface might turn silvery in appearance. Leaves may be streaked or spotted due to the lack of chlorophyll.
Mites favour warm, dry weather. So, increasing humidity and, if possible, decreasing the temperature can help prevent infestations. Mites can effectively be managed by entomopathogenic fungi Paecilomyces fumosoroseus @ 2g/L of water.
In severe conditions or as a last resort spray the crop with any one of the following insecticides alternatively by Dicofol (Kelthane) or Fosmite or Omite (Propagite) or Bifenthrin (Talstar) at 0.025% and repeat the spray at 10-15 days intervals to provide effective control against mites.
Snails and Slugs
These molluscs chew on the growing tips and leave holes and notches on the leaf. They are nocturnal feeders and leave a trail of slime behind them. The application of diatomaceous earth, sawdust to create a barrier is useful. Bait trapping by placing beer in a shallow plate is also effective.
Cockroaches are polyphagous insects and cause damage by eating away the new shoots and roots. Bait of boric acid, sugar, and flour mixed with water can be used. Catching and killing these insects is also effective.
It is caused by the fungus Sclerotium rolfsii under hot and humid conditions. It causes root and collar rot of the plant. If not detected early, it becomes almost impossible to save the plant.
The presence of mycelial webs with numerous small white, later orange-brown colored mustard seed-shaped sclerotia can be seen on the infected tissue and on the media. Drenching with fungicide Bavistin can manage this disease.
This fungus causes root rot. Rot occurs when drainage is poor or the plants are overwatered. The roots usually show a brown rot with white or brown fungal growth. In severe infections, the fungus girdles and kills the plant.
The infection quickly invades the lower leaves of small seedlings when it comes in contact with the media. Drenching with fungicide Bavistin @ 3g/L before planting helps prevent infection.
Botrytis Blight of Petal
The disease is caused by the fungus Botrytis cinerea. Numerous little black or brown spots are seen on the flower. High humidity and water droplets on the flowers encourage this fungal disease.
Avoid excess humidity and remove wilted infected blooms regularly to stop the spreading of this disease. Spray with Bavistin @ 1g/L of water or Indofil Z @ 2g/L at 7 days.
Bacterial Soft Rot
The causal organism is Erwinia carotovora. Water-soaked spots on leaves expand rapidly. The leaf becomes completely soft and slimy and emits a bad odour.
Good, healthy planting material should be used to manage this disease. Spraying 20% hydrogen peroxide @ 5ml/L or antibiotic Streptomycin @ 200ppm also helps.
Caused by Pseudomonas Spp, it produces brown patches on leaves, having oily spots surrounded by a yellow halo. Management practice includes the use of healthy planting material, rouging of infected plants, maintaining proper humidity, providing optimum nitrogen, and spraying antibiotic Streptomycin 300ppm.
Phalaenopsis chlorotic spot virus
It produces chlorotic spots on the leaves reducing the photosynthetic capacity of the plants. This virus is transmitted both mechanically and by aphids. Use of sterilized instruments, rouging and burning of infected plants, and managing aphids are recommended to manage this disease
Odontoglossum ringspot virus (ORSV)
Symptoms caused by the virus are variable, difficult to pinpoint, and sometimes, even, asymptomatic, but still experience a reduction in vigor. Common symptoms are irregular chlorotic or necrotic lesions of various sizes.
Yellow stripes may also occur. Circular ringspots, yellow to red lesions, with or without necrotic centers, can be observed in some hybrids. It is important to remember that there is no cure for this viral disease. But it can only be prevented by using healthy and virus free planting materials
Capsicum Chlorosis Virus (CaCV)
It is an isometric tospovirus. Symptoms include chlorotic spots with centric necrosis or chlorotic ring spots on the leaves. Apical necrosis and leaf distortion are also observed in severe case.
This virus can be transmitted mechanically or by sucking insect vectors like thrips, aphids etc. It can be managed by controlling insect vectors, using sterilised cutting tools, healthy planting material, and rouging out infected plants and destroying it.
It is caused by overwatering as the excess water is absorbed by the roots quicker than it is lost by the leaves, which can cause swelling of plant cells and produce a lesion resembling a blister.It occurs during cool weather when water quantity and/or frequency is not reduced. The blister-like symptoms can appear on upper or lower leaf surfaces, stems, petals or sepals.
Sunscald or Sunburn
It occurs during summer with high day temperature can increased leave temperature and leads to sunburn. Phalaenopsis are shade lowing plant direct sunlight will harm the plant White thin patch with a dark yellow ring is the common symptom.The patch will dry and will not spread anymore if acclimatized to suitable light conditions. The plants will resume normal growth. However, the damage done is irreversible. Care should be taken that the patch may not turn into rot.