Q: In my neighborhood we have several Sabal palms, which are planted in common areas that are covered with a snow-like fungus. What is it and how can we treat it?
A: The snow-like covering on your palms is not a fungus but an insect called Sabal Palm Scale or Palmetto Scale, Comstockiella sabalis. This insect is a common, native insect pest of palms, especially Sabal palms. Females give birth to live young and may form extensive colonies on palm leaves, which causes yellowing of the leaf. Their mouth parts pierce into the leaf tissue and they suck out the plant fluid causing a loss of chlorophyll. Armored scales are protected by a waxy scale covering composed of secretions and occasionally cast skins, which form thick, wafer like layers when insect densities are high.
In your case, the densities are extremely high probably because no one has been caring for these palms. It is important to scout the plants at least once a week to catch the insects early when it is easier to treat them with chemicals. Take a clean, damp paper towel and wipe off as much of it as possible – dispose of the used towels in a plastic bag before tossing them in the trash. Spray the fronds and trunk with horticulture oil or insecticidal soap which can be purchased at most garden centers. Follow the directions on the pesticide label and reapply as directed. These “softer” chemicals will be very effective on the young crawler stage, which I was able to detect in large numbers from the specimen you brought to the office. A strong chemical will not be able to penetrate the waxy coating and will therefore be ineffective.
Palm scale numbers are controlled naturally by tiny wasp parasitoids (Aphelinidae: Coccobius sp.) that develop in the body of the scale. However, these wasps can be killed if strong insecticides are used, which then causes the populations of scale to soar. In addition, a systemic pesticide could be used but do so sparingly. These products are potent and expensive. As always, follow the directions on the label as these chemicals can cause problems for some of our important animals.