Orchid viruses
Also known as Cymbidium mosaic virus (CymMV), Odontoglossum ringspot virus (ORSV)
In short
More than 27 viruses infect orchids, but two dominate worldwide: cymbidium mosaic virus (CymMV) and odontoglossum ringspot virus (ORSV). Both spread mainly on cutting tools and through division, persist for long periods on tools and in media, and cannot be cured. Mixed infections are common and cause worse symptoms.
How it looks
CymMV causes irregular yellow (chlorotic) patches, mosaic and sunken or dead (necrotic) streaks on leaves, especially new growth; Phalaenopsis may show yellow oval or elongated streaks that turn purple-black, and Vanda shows chlorotic (pale) flecks. Cattleya flowers can develop brown necrotic streaks 5–21 days after opening. ORSV causes chlorotic ring spots, mosaic or necrosis on leaves (diamond-shaped mottles on Cymbidium, slightly sunken yellow areas on mature Oncidium leaves) and colour-breaking or distortion of flowers, especially in lavender cattleyas; root-tip death is common. Some infected plants look completely normal.
Signs
Mottled, streaked or ring-spotted leaves; smaller, fewer, streaked or distorted flowers; stunted growth; poor vigour; brown streaks appearing on flowers some days after opening.
Life cycle
Both viruses live in the plant's sap throughout the plant. They are transmitted mechanically: on knives and shears used to cut flowers or divide plants, by dividing infected plants, by contact between plants, and on hands. They remain infectious on tools and in used media for long periods. Some insect transmission has been reported.
What favours it
Risk rises with shared or unsterilised cutting tools, dividing many plants in one session, reusing pots and media, crowding plants so leaves touch, and buying untested divisions.
Prevention
- Sterilise cutting tools between every plant — for example by flaming, a 10% bleach solution or trisodium phosphate.
- Buy virus-tested plants, such as meristem (tissue-culture) propagated stock, and quarantine new orchids.
- Do not reuse pots unless they are cleaned and soaked in a sanitising solution; replace old media.
- Keep plants from touching and wash hands between plants when repotting or cutting flowers.
Treatment
Start with the first step and move down only if the problem persists.
- There is no cure; discard and destroy infected plants.
- If you suspect a virus, isolate the plant and have it tested (ELISA test kits and laboratory tests can confirm infection, even before symptoms).
- After handling a suspect plant, sterilise tools, benches and hands before touching other orchids.
Pros and cons
Cons
- Incurable and permanent.
- Symptomless carriers can infect the rest of a collection.
- Reduces flower number, size and quality.
Look-alikes
- Orchid black rot
- Black rot forms spreading, wet, purplish-black patches that move quickly through leaves and pseudobulbs; viral lesions are streaks, rings or mottles that do not rot.
- Sunburn
- Sun scorch appears on the most exposed leaf surfaces soon after a change in light and does not form rings or streaks along new growth.
- Cold damage
- Chilling produces pitting or blackened patches after a cold event across several leaves at once.
- Fungal leaf spot
- Fungal spots are usually discrete spots that enlarge, often with fruiting bodies, not streaks or ring patterns.
Affected plants
CymMV has been found in at least 56 orchid genera and ORSV in about 20, including Cymbidium, Phalaenopsis, Oncidium, Vanda, Dendrobium and Cattleya relatives. CymMV infects only orchids.
Related
Sources
- Orchid — Virus Diseases, Pacific Northwest Plant Disease Management Handbook
- Cymbidium mosaic virus — Wikipedia
- Odontoglossum ringspot virus — Wikipedia
Written in our own words from these sources. Check a product label before using any treatment.