Vanda Orchid Diseases

Gray Mold

• Gray mold is a disease that is caused by the fungus Botrytis cinerea. This disease is commonly seen in orchids, African violets, ferns, figs, dusty millers, passion flowers and poinsettias. According to the University of Illinois Extension website, gray mold symptoms include browning of flower petals and brown lesions on them. Gray mold also causes webbing to develop on the flower, which is known as mycelium. This webbing usually occurs during periods of moist, humid weather. Gray mold can kill flower petals, buds, shoots, seedlings and leaves. Gray mold overwinters in dead plant material, so destroying dying orchids and their debris is important in controlling the spread of the disease.

Algal Leaf Spot

• Algal leaf spot is caused by the algal Cephaleuros virescens, according to the Alabama Cooperative Extension System. There are a variety of plants that are susceptible to this disease, such as the orchid, jasmine, juniper, magnolia, pecan, privet and wisteria. The symptoms associated with algal leaf spot include spots on leaves that are pale green or red, cracking of twigs and branches and lesions that may girdle the plant. Wet, rainy weather encourages the spread of this disease because it is spread through water droplets and rain.Controlling algal leaf spot in orchids is accomplished by practicing good sanitation, removing spotted leaves from plants and pruning trees in close proximity to the infected plants, which helps the orchids dry more quickly after rain.

Rot Diseases

• Bacterial diseases often progress at a rapid pace and can affect orchids. Orchids that suffer from bacterial diseases may have a foul odor and parts of the plant look wet and decayed. Brown rot is caused by Erwinia sp. and is often fatal to orchids. The symptoms associated with brown rot include wet spots on leaves and bulbs that turn brown in color. Orchids infected with brown rot can die within just a few days of infection. Soft rot is another type of bacterial disease that can attack the Vanda orchid. The symptoms associated with soft rot include lesions of brown decay on the orchid. Warm temperatures favor bacterial diseases and allow them to progress quickly. Bacterial diseases are serious and the orchid may not be saved in cases of severe infection, states the Missouri Botanical Garden.