Why Do Leaves Turn Yellow & Fall Off of Orchids?

The orchid family consists of thousands of exotic plants and trees valued for their vibrant flowers. Leaf yellowing and leaf drop are common symptoms of disease and insect infestation. While orchids are generally free of serious growing problems, disease and insect infections can cause leaf yellowing and drop. Early identification and control for these orchid disorders are vital for reducing the severity of disease and insect infestation.

Cymbidium mosaic is a common, but serious, viral disease of orchid foliage. The disease causes yellow steaks on orchid foliage, leaf drop, chlorosis or yellowing and black streaks. The disease ranges in severity depending on the orchid species infected. Some orchid species exhibit minor cosmetic symptoms, while others can exhibit severe chlorosis and leaf death. The virus transmits between orchids through insects that carry the disease. Severe infections cause reduced vigor, which slows the growth of blossoms. Destroy infected plants to reduce the spread of the disease. However, insecticides are an effective method for preventing insects from infecting orchids.

Boisduval scale is a serious, worldwide pest of orchid that can cause plant death if left untreated. The Boisduval scale is a small, hard-shell insect pest that feed on plant tissue, causing small circular patches of chlorosis. Chlorosis is the yellowing and death of plant tissue. Severe infestations can cause leaf yellowing of the entire orchid, leaf drop and plant death. South Dakota State University recommends dabbing mature scales and plant tissue with rubbing alcohol to remove the pest. However, insecticides are an effective method of control for scale larvae and immature scales. Once the scale matures and creates its hard shell, insecticidal control loses its effectiveness.

Lace bugs are small insect pests of orchids that cause symptoms similar to nutrient deficiency. The small insects suck nutrients from the underside of leaves, causing leaf yellowing and leaf drop. Nutrient deficiencies can cause leaf yellowing similar to lace bug infestations; however, lace bugs cause leaf drop, which separates the symptoms. Wash infected orchid leaves with a soapy water solution for minor to moderate infestations to control the insect. Insecticidal control is effective for severe infestations.

Ringspot is a viral disease of orchid caused by a strain of the tobacco mosaic virus. The virus transmits through plant-to-plant contact, which includes root contact and pruning equipment. Infected weeds can also transmit the virus to orchids. Symptoms consist of yellow foliage, yellow leaf streaking, leaf curl, leaf drop and leaf death. The disease rarely causes plant death, but it does cause reduced vigor and cosmetic damage. Prevent infection by controlling disease-spreading weeds with target herbicides.