The Dendrobium orchid genus encompasses approximately 1,200 varieties. A wide range of sizes and flower colors exist. Some varieties sport flowers that last only a day, while others linger for weeks. Each orchid member of the genus has its own cultural requirements to flourish, but most share common foliage diseases that can easily afflict the plant.
The leaves of orchids infected with the orchid virus (Odontoglossum ringspot virus or Cymbidium mosaic virus) exhibits yellow spots or reddish-yellow lesions. The yellowing may have a striped effect instead of the basic spotting that most often appears. Some orchid varieties show purple blotching on the foliage. The leaves may begin to curl downward in an unnatural way. A few orchids may be asymptomatic but still be infected with one of the viruses.
Once a plant is infected, there is no cure, according to the American Orchid Society. Breeders have managed to breed resistant plants. Promptly discard infected orchids. Aphids, thrips and mites can easily transmit the viruses.
Basal rot, a fungal disease, occurs at the base of the plant in the beginning. The disease may go unnoticed until it spreads upwards on the plant and causes the foliage to wilt. Black discoloration may occur. Once the rot has progressed significantly, the orchid plant dies. Steps can be taken to try to cut away the areas of rot if the damage is not too extensive. Infected foliage of smaller plants can be removed. Keep the orchid plant relatively dry once the areas of rot have been removed so that the disease does not reoccur. Apply fungicide for orchids to the orchid plant’s foliage to help control the disease and prevent its spread.
The disease occurs from over watering or allowing the orchid to sit in standing water in a saucer or tray. Excessively humid conditions can also cause the rot to occur. Failing to clean the pots prior to transplanting an orchid can also cause the fungus. Using infected soil will also result in the orchid contracting the fungus.
Fusarium wilt causes the foliage of the orchid to take on a gray appearance. The leaves will begin to shrivel. The disorder usually occurs if the orchid does not receive ample water, but over watering can also cause it.
To save an orchid afflicted by the disorder, promptly remove it from the pot. Remove all the medium from around the orchid’s root system. Observe the roots closely to see if there are any that are still alive. Cut away the diseased roots and discard. Repot the viable roots in new medium in a new pot. If none of the roots are healthy, destroy the entire plant.
After repotting the healthy plant place it in an area with diffused light. Mist the plant twice a day to help raise the surrounding humidity. Keep the orchid moist but not overly damp. The plant may not grow new foliage until the following season.