Green Scale (Coccus viridis)

This is a member of the soft scale insect group and one that is easily overlooked because it is flat and an almost transparent pale green. Because this is one of those honeydew excreting insects, the associated black sooty mold growing on the honeydew will catch your attention and cause one to take a closer look for insect pests. Green scale attacks coffee, citrus, gardenia and some other ornamentals.

The sooty mold on these ixora leaves and flower structures indicates an insect infestation. A close look reveals that it is severely infested with green scale. Note the crawler stages with the adult female scales in the photo on the right..

These sucking insects cause premature defoliation by robbing the plant of nutrients. They tend to congregate on the underside of the leaves along the mid-vein. There are repeating generations, every 50 to 70 days, which means one has to inspect plants on a monthly basis for this pest.

What to do: Use a 2% horticultural (paraffinic mineral) oil solution when the smaller stages are present. The oil will also dry up the sooty mold and it will flake off. A new soil drench systemic (root absorbed and translocated to the leaves) product became available to the homeowner this year, called Bayer Advanced Garden Tree and Shrub Insect Control. That's a pretty generic name, so look for the active ingredient, imidacloprid. This systemic has a nice toxicology (in regard to human safety) and a nice (low) environmental impact, compared to older systemic insecticides. It also gives prolonged protection, maybe 4 to 12 months depending on how much organic matter is in the soil. However, this product is not labeled for use on citrus and other fruit bearing crops. Also, get rid of the ants! Use ant bait stations on the soil to keep the ants from moving up the trunk and moving the scales to new plants. The ants reportedly protect honeydew producing pests from predators and parasites.

Courtesy of Doug Caldwell, Ph.D. Landscape Entomologist, Certified Arborist and the Commercial Horticulture Extension Educator with the University of Florida Collier County Extension.