Watch Out for Cottony Cushion Scale
In our state, you see many insects on ornamental plants including those known as scales. Scales are a diverse group in Florida, with over 180 species. Many of these do very little damage to plants but some are quite destructive, once of which being the Cottony Cushion Scale (Icerya purchasi).
These are currently active in our landscape, as evidenced by the sample picture in this article that was found feeding on Knockout Roses at our office. However, the main plant of concern that this pest targets is citrus trees.
Cottony Cushion Scale was introduced by accident to Florida from Australia over 100 years ago and is know found on citrus trees worldwide. They go through several life stages that look quite different from one another but are fairly easy to identify once you see them.
The most noticeable life stage is the adult, which is often found on larger stems or branches. The body itself is a small red structure with a white waxy coating but the egg sac with its parallel ridges stands out heavily on the hermaphroditic female. The males look much different, with a dark red body and wings.
Younger growth stages look different as their waxy shell is being produced. The most damage is actually done by the young nymphs, where they line up in rows on the midribs of leaves and small twigs to feed. The younger nymphs are also more mobile and are about the size of a pin head and are a bright red-orange color.
If left unchecked with favorable conditions, the scale can cause defoliation, leaf drop, and decreased tree health. The scale also produce a sugary substance, known as honeydew that can aid the growth of sooty mold on the plant.
Control of the Pest
For cottony cushion scale, there are some control options. One of the most effective is the use of horticultural oils to smother the insects. This is best applied when the scale are in their younger nymph stages, so make sure to regularly check your landscape for pests. These oils can also be applied during the winter when the scales go dormant in the cold. Horticultural oil is fairly safe but be sure to follow all of the guidelines and directions listed on the products label and avoid applying it on hot, sunny days. These applications are most effecting on smaller plants, where complete coverage can be achieved rather than on a larger tree.
Other chemicals are available that can control this pest but they can also lead to negative side effects such as increases in populations of other pests or a decrease in natural predators, leading to outbreaks of the scale in the future.
For more information on this pest, visit http://edis.ifas.ufl.edu/in161.