Rubber plants are durable plants with leathery leaves and a single erect stem when they're young, although older plants will branch out. They're easy to grow and don't require a lot of care, making them a popular choice for those with a less-than-green thumb. . Sometimes, however, rubber plants can develop discolored leaves and white, brown or yellow spots.
Rubber plants suffer from sunburn when they're suddenly exposed to too much light. This can happen when plants that are used to low light are moved to a brighter spot. Symptoms include the appearance of yellow or white spots and patches on the leaves. The spots may turn brown as tissue dies, and the leaves may fall off the plants. Don't worry. When the new leaves come in, they will be adapted to the brighter light. If you move the plants back into low light, the leaves will fall off again and new ones that are adapted to low light will begin to grow. Sometimes it helps to acclimate your rubber plant to bright light in stages, gradually moving them into brighter and brighter locations until they're placed in their final spot.
Mealybugs are small pinkish or yellowish insects that are covered with white filaments. They grow about 1/8 inch long and damage plants like rubber plants by feeding on their sap and excreting a sticky substance called honeydew which attracts sooty black mold. Symptoms of mealybug infestation include wilted and deformed leaves as well as leaves that are covered with black spots from the sooty mold growing on them.
Scales are small round insects with no recognizable body parts like a head. They're also unusual because they don't move. Instead, they attach themselves to plants and suck the sap out of the leaves. Symptoms of scales on rubber plants include yellow spots on the undersides of leaves, leaf yellowing, dropped leaves and the appearance of black sooty mold, which is attracted to the honeydew that the scales excrete.
Control scales and mealybugs by pruning infested leaves and destroying them. Increase air circulation between plants by not crowding them, and avoid over-fertilizing because these insects lay more eggs on plants that receive a lot of nitrogen. Avoid using pesticides, if possible, because pesticides kill natural predators like ladybird beetles, green lacewings and parasitical wasps. If necessary, horticultural oils can be used to control scales and mealybugs.
Several fungus infections cause spots and discolored rubber plant leaves. Anthracnose can be identified by yellow spots that appear all over the leaf. These spots turn dark brown and the may cause the leaves to fall off the plant. Botrytis blight causes large tan and brown spots to form on leaf tips or between the leaf and sheath. Small red or dark green spots on the lower surface of your rubber plant indicate a cercospora leaf spot infection. To control fungal infections, avoid overhead watering, provide good air circulation, and prune diseased plant parts and destroy them. Fungicides can also be applied.
- University of California Cooperative Extension: Spots on Rubber Plant
- Bella Online Houseplants Site; Ficus Elastica, the Rubber Tree; Lisa Beth Voldeck
- New Mexico State University Southwest Yard and Garden: Sunburned Ficus
- University of Florida Ficus Production Guide; R.W. Henley, et. al.
- Cornell Cooperative Extension; Care and Selection of Ficus; Cynthia D. Mitchell