Scale Insects on Ficus

Question:

My indoor ficus leaves and branches have sticky brown lumps. What is wrong? What can I do?

- J.K. Willis

Answer:

This is a good description of scale insects on indoor ficus (Ficus benjamina, F. retusa, F. indica, etc.). These damaging insects may also infest other houseplants, so it is important to manage the problem and prevent their spread. This topic has been discussed in Yard and Garden before, but it is an important consideration at this time of the year as we are beginning to bring houseplants indoors after a summer outside. The sticky substance is the honeydew excreted by the insects. The bumps are adult scale insects under their waxy coverings that make them difficult to treat with insecticides.

There are a variety of treatment options available - some treatments preferred by one author, others preferred by another author. Chemicals are most effective when used to treat the juvenile (crawler) form of the insect before they have formed their protective covering. At this time horticultural oil and insecticidal soaps are very effective. (Both have very low toxicity to mammals us!) These products can stain fabrics, so cover carpets, upholstery, and draperies if you apply these (or any other product indoors).

Some authors recommend use of systemic insecticides to kill the adult phase of this insect. Contact insecticides are ineffective because of the scales protective covering, but systemic insecticides are absorbed into the plant and then into the insect when it feeds on the plant juices. This product is more toxic to us and our pets, so it is safest to apply it outside and leave the plant in a shady location until the chemical has dried.

Some authors prefer to recommend the use of mechanical control methods. They dip a cotton swab into alcohol and rub firmly enough to remove the insect (covering and all) from the stems and leaves. Some scale insects will rub off quite easily while others will require more effort. Take care not to bruise the plant when doing this.

As I mentioned in the beginning, this is a good time to be checking plants for insects and diseases before bringing them indoors. If they have been indoors, it is still warm enough to take them outside to a shady location to clean them up before their long winter stay indoors.

Plants that are severely infested with insects may be treated (mechanically or chemically) so that their problems will not spread to other plants, or they may be discarded and replaced with healthy plants from a nursery. New plants from the nursery should also be carefully inspected for diseases and insects. Problems are more easily treated now rather than in the middle of the winter when it is too cold to take houseplants outside for treatment.

Also, please join us on Southwest Yard & Garden, a weekly program made for gardeners in the Southwest. It airs on KRWG in Las Cruces Saturdays at 11:30 a.m., repeating Thursdays at 1:00 p.m.; on KENW in Portales on Saturdays at 10:00 a.m.; and on KNME in Albuquerque on Saturdays at 9:30 a.m.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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