Most orchid genera are affected by one or more virus diseases. With the increasing importation and rapid
exchange of plants by both commercial and amateur growers, the introduction and spread of viruses
among orchid plants in a grower’s or florist’s greenhouse is highly probable. Virus-infected plants bloom
less efficiently, lack vigor, and produce flowers of lesser quality than healthy plants. The introduction of
virus-infected stock not only costs the grower and florist in terms of greenhouse space, but also presents
a dangerous virus reservoir that may serve to contaminate other orchid plants and seedlings.

The efficient control of orchid virus diseases depends on rapid and accurate diagnosis, followed by the
destruction of diseased plants. The symptoms produced by orchid viruses depend on the particular viruses
and strains involved; the hybrid, species, and genera of orchids infected; the age of the leaves; the time
of year; and the environmental conditions. The same virus may cause widely different symptoms on
different genera, e.g., a flower breaking on the blossoms of one genus, a bar mottle or other symptoms
on another genus. Virus-like symptoms also may be produced by thrips on Vanda and by scales and mites
feeding on Cymbidium leaves. Abnormal nutrition and fungal infections also produce virus-like
symptoms.

Symptoms in flowers may also be mistaken for those caused by a virus. Aphids and thrips have been
reported to damage Cymbidium and Vanda flowers, respectively. Thrips injury is very similar to a virus
disease in Vanda orchids. Some virus-infected plants may show no symptoms. Such symptomless plants
are excellent virus “carriers” for they go unnoticed in the greenhouse. Under adverse conditions, these
symptomless plants may develop strong symptoms. Virus symptoms also may vary between plants that
are grown under different conditions. Plants infected with more than one virus also express variable
symptoms.
Growers should be familiar with the common orchid virus diseases. Much worry can be overcome by
isolating suspect plants and employing stringent control measures. These factors make the diagnosis of
orchid diseases difficult.

Symptoms
1. Leaf necrosis, black streak. Lead necrosis, caused by the cymbidium mosaic virus, is probably
the most common virus disease of many kinds of orchids. Infected plants have irregular, brown-toblack,
elongated spots and streaks of dead tissue on both surfaces of older leaves (Figure 1C and
1D). Infected leaves that show symptoms tend to age quickly and dry up. Flowers from such plants
are usually symptomless, but they may open in an unthrifty manner. If the leaves die prematurely,
the flowers are usually fewer in number and of smaller size. Diseased plants are usually less
vigorous; however, not all infected plants show symptoms. Spread of the virus is usually via
contaminated pruning tools. No insect vector is known.
Leaf necrosis affects Cattleya and its hybrids as well as many species of Angraceum, Cymbidium,
Epidendrum, Laelia, Oncidium, Spathoglottis, and Zygopetalum.
Certain strains of the tobacco mosaic virus also produce leaf necrosis on Cattleya (Figure 1B),
Cymbidium (Figure 1E), and other orchids that closely resembles symptoms produced by the
cymbidium mosaic virus.
2. Mild flower break. This is caused by a strain of tobacco mosaic virus. Mild flower breaking is
much more common in Cattleya than is severe flower breaking. Affected plants have much less
variegation in the flowers than plants infected with severe flower break. The flowers are not
malformed, and the leaves have only mild mosaic symptoms. The means of transmission of this
virus is unknown.
Mild flower breaking has been reported on about 30 species and hybrids of Cattleya. This virus also
produces spots and rings of dead tissue on the leaves of Odontoglossum and diamond mottle on
Cattleya, Cymbidium, Odontoglossum, and Phalaenopsis. Diamond mottle is distinguished by
elongate chlorotic areas that are often diamond-shaped. Older leaves sometimes develop brown to
black flecks and streaks.