Commercial Floriculture

Pests and diseases

• Orchids are prone to a number of pests and diseases caused by various agents like viruses, fungi, bacteria, insect pests, etc.

The chart below identifies and illustrates types of damage to orchids and the various causes.

PEST	CAUSE/SYMPTOM	REMEDY
Aphids	Leaves and stems appear stunted; Flowers may be malformed or fail to open. Aphids are visible, particularly on new growth. Most vulnerable pest: Cattleya, Oncidium, Phalaenopsis	Wash off black fungus with water and mild kitchen detergent. Use an insecticide containing Malathion, Desis, Nicotine or pyrethrum.
Mealy Bugs	Cottony masses especially infest points of juncture such as the crook between two leaves. Plants may appear stunted or shriveled. Most vulnerable: Cattleya, Dendrobium, Phalaenopsis	Remove small infestations with a cotton swab dipped in methylated spirits. On heavy infestations, use an insecticide containing malathion or nicotine.
Scales	Causes sooty mould The plant may be stunted, with leaves yellowing and falling off. Most vulnerable: Cymbidium, Pahiopedilum, Miltonia, Zygopetalum, Cattleya,	Pick off small infestations with tweezers or a knife, or swab with methylated spirits. Spray adult scales with an insecticide containing malathion or nicotine.
Slugs and Snails	The plant is punctured with ragged holes and a slimy trail is visible where pests have passed. Vulnerable: All orchids, especially seedlings.	A tuft of cotton wool around the stem will protect flowers. Trap snails and slugs with pesticide bait containing metaldehyde or methiocarb.
Spider Mites	Leaves appear pitted or stipped with white. White webbing may show on the underside of the leaves. Most vulnerable; Cymbidium, Dendrobiu, Phalaenopsis.	Scrub and rinse foliage with warm water to break up webs. Spray heavy infestations with pesticide containing malathion or derris.

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Diseases

PEST/SYMPTOM	CAUSE	REMEDY
BLACK ROT: Purplish blotches edged with yellow appear on leaves and new shoots. Rotting may work downwards from leaves or upwards from roots and rhizomes. Most vulnerable: Cattleya Orchids, Phalaenopsis.	Black rot is caused by several types of fungi that favour high humidity, cool temperatures and standing water. Damping off, which affects seedlings, is also caused by these fungi and occurs most readily in community pots.	Drench infected plants with a fungicide such as captan or zineb. Remove infected parts cut 2.5cm into healthy tissue and seal cuts with fungicide. Destroy badly the diseased plants.
LEAF SPOT: Raised or sunken spots in yellow, brown or purplish shades spread quickly over leaves. In advanced stages, leaves turn yellow or brown and die. Most vulnerable: Oncidium, Dendrobium	Leaf spot is usally caused by those species of fungi that thrive in high humidity. IT is especially destructive to seedlings but rarely fatal to mature plants.	Reduce humidity and increase air circulation. Cut off diseased leaves; spray cuts with fungicide. Apply captan or a systemic fungicide containing binomial or thiphanate-methyl weekly.
PEATAL BLIGHT: Small brown circles, often with pink edges, appear on sepals and petals. Most Vulnerable: Cattleya, Orchids, Dendrobium, Oncidium. Phalaenopsis, Vanda	Petal blight, also known by the name of the fungus that causes botrytis, generally appears in cool, damp weather when there is inadequate air circulation. Microscopic spores are carried by insects, water or human hands. Fungus tends to attach old and fading flowers.	Cut off and destroy infected blossoms. Spray plants with a fungicide containing benomyl, captan, thiophanate-methyl, thiram or zineb.
VIRUS: Leaves may show yellow, black or brown pitting, mottling, mottling and streaking. Flowers too may be streaked or mottled. Vulnerable: All Orchids	Two main types of viral diseases, cymbidium mosaic and Cattleya mosaic, spread through the vascular systems of plants. Highly infectious, viruses may be transmitted by infected plants. Highly infectious, viruses may be transmitted by infected plants, hands, fools, aphids.	There is no cure. Destroy infected plants. When dividing, flame sterilizes the knife between cuts, dip potting sticks in a10 percent household bleach solution.

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As a general rule:
1) Apply fungicides and insecticides early in the morning or late in the evening.
2) Use a fine nozzle for spraying.
3) Heavily infected plants should be discarded and burnt, and should not be used as propagating material.

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