Q. We have a five-year-old Ficus plant that has sentimental value to my wife since it belonged to her mother. This past summer we noticed what we think are scale insects forming on the branches of this weeping fig. We removed the brown bumps as soon as we found them, and the Ficus seemed to be doing well. But now the plant has started dying off. It’s down to one healthy branch with some faint signs of new growth. No sign of the scale, but I don't know what the early signs of scale are. I just know the large brown bumps. What do I need to do to get this plant back to good health? Right now I am watching for more scale to appear, and watering it several times a week with a Miracle-Grow mix. Will the scale come back, and if so what can I do to get rid of it once and for all?
A. There are several species of scale insects that infest weeping figs (Ficus benjamina). If you are not seeing the brown bumps, you have them under control for the moment. Continue monitoring the plant for them, and physically remove any that you find. Immature scale insects are known as crawlers, because it is the only time in their life cycle that they are mobile. They range in color from yellow to orange-yellow, but they are very small and can be difficult to see. Once they settle into place on a stem or leaf, they insert their piercing-sucking mouthparts and begin to feed. Then they secrete a waxy coating over themselves that protects them from predators and makes them almost impervious to insecticide applications. Physical removal works over time, and is much safer than using an insecticide indoors.
I am concerned that you are overwatering this plant. Now that it is down to “one healthy branch,” it does not use as much water as it did when it was full. By watering several times a week, you may be keeping the soil too wet, which will eventually lead to root rot. Allow the top couple of inches of soil to dry thoroughly between waterings. Stick a finger into the potting mix and feel, rather then guessing.
Consider repotting your ficus, especially if it has been growing in the same container for a while. You will be better able to judge the health of the roots once you remove it from the pot and get a look at the root system. It the roots are white and firm, they are still healthy and you can replant the tree in fresh soil in the original pot. If the roots are brown and mushy, that is a sign of root rot. Trim the ailing roots back to healthy ones as much as possible and repot the tree in a smaller pot. This reduces the soil volume and allows it to dry faster between waterings.
Although your impulse to fertilize this plant to help it recover may seem intuitive, it may cause more harm than good. Fertilizers are basically salts, and salts can build up in the soil over time. If you have ever noticed a white, crystalline substance on the soil surface or the sides of a clay pot, you have seen soluble salts. They can build up on the roots, too, and burn any tender new roots that the plant produces. Also, if this plant is suffering from root rot, you do not want to push new top growth that the reduced root system cannot support. Hold off on fertilizing your ficus any more until the root system recovers. You will know because the plant will begin to sprout more healthy new growth. You can also pop it out of the container from time to time to examine the roots. Firm, white roots are also evidence of recovery.
We typically do not recommend fertilizing houseplants in the winter, from October through late March or early April. Our houseplants are not actively growing during the gray days of a typical western Pennsylvania winter. Resume fertilizing in spring, when houseplants respond to increased light levels outdoors by putting on new growth. Always read and follow label directions as to how frequently to use a fertilizer and how to mix it – more is never better when it come to fertilizer.
Excessive nitrogen fertilizer can make plants MORE susceptible to damage from insects such as scale, that feed with piercing-sucking mouthparts, because nitrogen is a critical nutrient for them. By fertilizing too frequently, you may actually be creating a situation that favors the scale.