Ficus trees (Ficus benjamina), also known as weeping fig, are popular container-grown houseplants. Many ficus owners take their small trees outdoors in the summer months to allow the sun and rain to restore their winter-weary plants. While ficus trees enjoy their summer respite, they can attract thrips--small, soft-bodied insects that damage leaves and buds. Before bringing your tree inside, identify and take steps to control thrips.
Greenhouse thrips (Heliothrips haemorrhoidalis) are the most common species to attack ficus trees. Feeding on the underneath side of mature leaves, greenhouse thrips are approximately 3/64 of an inch long. Their bodies are slender and black with a silver sheen and leave a sticky, varnish-like excrement on leaf surfaces. Larvae are translucent and white. Thrips like a moist, shady environment and will not reproduce in large numbers under hot, dry conditions.
Thrips are sucking insects, and their feeding habits damage mature leaves. Your ficus's leaf surfaces will develop bleached areas and young leaves may be deformed. Extensive thrip damage will cause leaves to wilt, dehydrate and drop. The varnish-like excrement inhibits transpiration, further stressing your plant. Wipe this material off the leaves with a soft cloth dipped in rubbing alcohol.
Many species of thrips are difficult to control with available chemical pesticides because of their small size and mobility, but greenhouse thrips are slow moving and susceptible, according to the University of California Integrated Pest Management Program. The program states that "thoroughly applying most any insecticide will kill this species" although it further recommends "good cultural practices and conservation of natural enemies with the use of least-toxic insecticides, such as narrow-range oils."
Low-toxicity sprays include pyrethrins combined with piperonyl butoxide and insecticidal soaps. Neem oil is very effective against greenhouse thrips.
Close observation of your ficus tree can identify and stop an impending thrip outbreak. Use bright yellow sticky traps, available at garden centers, to capture early thrip settlers. Caught early, thrips can be managed with minimal chemical controls.
Also keep your ficus trees pruned. Remove damaged leaves and broken branches. Do not allow containers to sit in the standing water of a drainage tray. This creates a damp environment favorable to thrips. Always place a layer of gravel in the tray to elevate the bottom of the pot.
Several species of beneficial insects feed on thrips. Green lacewing larvae, ladybugs beetles, parasitic wasps and predatory mites are available at many nursery and garden centers. Released around your ficus trees, these harmless (to humans and pets) arthropods will devour thrips and thrip larvae.
Verticillium lecanii is a fungal pathogen that penetrates the thrips outer cuticle. According to Cornell University, "once inside the insect, the fungus rapidly multiplies throughout the body. Death is caused by tissue destruction and, occasionally, by toxins produced by the fungus." As an added benefit, the fungus can emerge as the insect's body decays, spreading the deadly fungus to other thrips.