Brown Spots on My Ficus Rubber Tree's Leaves

Don’t Leave it Out in the Cold

• Rubber trees are tropical plants that thrive only in U.S. Department of Agriculture plant hardiness zones 10 to 12. They are extremely sensitive to cold temperatures. When exposed to cold, the mature leaves will develop big brown spots. The younger leaves will pucker and turn brown.

Warm it Up

• Nothing can be done about the brown spots that have already developed, but the rubber tree will usually recover. To prevent future damage, do not set the plant near an air conditioner. Bring the rubber tree indoors when temperatures drop below 50 degrees Fahrenheit. Serious damage is sustained if the temperature drops to 40 degrees Fahrenheit.

Did that Spot just Move?

• Small brown spots on the rubber tree leaves are probably scale insects. They are only 1/8 to 1/3 inch, oval or round and are often tan or brown, although they can be many other colors, depending on the species. Because they are flat and immobile or extremely slow-moving, they look more like spots in the leaf tissue than insects on the leaves. They find an area they like, usually on the underside of a leaf, sink their tiny mouth parts into the leaf tissue and suck the juices out. Some scales may be on the rubber plant stems. Many types of scale insects excrete honeydew, which is a sticky, clear liquid. A severe infestation may result in wilting or yellowing leaves.

Scrub a Dub Dub

• Confirming that the spots are scales is fairly easy. Simply try to peel one of them off the rubber tree leaf with a thumbnail or the dull edge of a butter knife. If they are scales and they have excreted honeydew on the leaves, set the plant in the bathtub and wash the honeydew off with water. Scrub the scales off the leaves gently with an old toothbrush, or dip a cotton ball in isopropyl rubbing alcohol and wash them off with that. Check the leaves every other day or so for new scale insects, and repeat the treatment as necessary until they no longer return. For more stubborn infestations, the rubber tree can be sprayed with ultra-refined superior horticultural oil. Mix the oil with water at a rate of 1 or 2 ounces for each gallon of water. Pour the solution into a bottle and spray the plant thoroughly. Be sure to coat the undersides of the leaves and stems. Weather permitting, the rubber plant should be taken outdoors and set on newspapers before spraying it, otherwise set the plant in a well-ventilated room. Let the oil dry before returning it to its usual space. Spray it again if the scale insects return.