The Florida wax scale has become an increasing problem on ornamental plants in south Louisiana. Although it infests a wide range of host plants, including shrubs, trees and several non-woody plants, Florida wax scale is a particular problem on ornamental hollies.
“These insects suck plant sap, removing carbohydrates that otherwise would be used for plant growth,” said LSU AgCenter entomologist Tim Schowalter. In addition, foliage of infested plants becomes blackened by sooty mold growing on the honeydew these insects produce.
Control is difficult on heavily-infested plants, in part because insecticide treatments require proper timing and thorough coverage. “Even after the insects are killed, many of the scale parts and the sooty mold will remain on the plants and continue to disfigure them,” Schowalter said.
Unlike other insects, the wax scale is globular and is coated with a heavy layer of white, beige, pinkish-white or grayish wax. Beneath the wax covering, the scale’s body is reddish, and the adult female is about 1/8 inch in diameter.
“The scales are easily spotted because most colonize the upper surface of leaves. This makes the scales more easily targeted with foliar insecticide sprays. However, some of the scales colonize the underside of leaves and on twigs and branches where they are more protected.”
Severe infestations cause discolored leaves, dead shoots or branches and occasionally plant death. Large amounts of sugary honeydew can become home to sooty mold fungus.
“The fungus makes infested plant parts black and unsightly and can interfere with photosynthesis,” Schowalter said. “Honeydew attracts a variety of insects, especially bees, wasps, hornets and ants, and hummingbirds that feed on the high-energy liquid.”
The scale can be controlled by replacing heavily infested landscape hollies and other host plants with non-host species to eliminate repeated insecticide treatments. Alternatives to hollies include ligustrum, privet, boxwood, pittosporum, bottle brush, sea grapes, oleander and regular or dwarf wax myrtle.
“Of course, these other landscape ornamental plants may have other limitations,” Schowalter said. Purchased hollies should be carefully inspected to avoid purchasing already-infested plants.
Scales will cause less damage if plants are kept vigorous and healthy through proper selection and preparation of planting sites and by providing adequate water and fertilizer.
Regularly inspecting plants for early signs of infestation and prompt control can minimize damage.
“Infested plant parts can be pruned and discarded. Sanitation and pruning will reduce initial pest density and open the canopy for improved spray coverage.”
Appropriate insecticides will eliminate scales and prevent new infestation by crawlers that disperse by ballooning -- or hitching a ride on air currents.
Recommended insecticides include either soil-applied or foliar-applied systemic products containing imidacloprid as an active ingredient. Follow label directions for control of “scale insects” or “soft scale” on ornamental landscape plants.
“Systemic insecticides generally do not eliminate all scales located on branches or twigs, so the addition of foliar treatments may be necessary to eliminate the whole population,” Schowalter said. “Complete coverage of all plant surfaces is essential.”
In addition to imidacloprid insecticides, insecticidal soap also can be used for control as an alternative to harsher chemicals. “But it is even more important to ensure complete coverage if using soap because the effectiveness of this material depends on sufficiently covering the scales to suffocate them.”