If you have Hollies, Camellia, or Laurels, odds are that you’ve noticed a “sooty” black mold growing on the tops of the leaves or that the leaves are yellowing and dropping leaves. Most home gardeners attempt to treat these symptoms as a disease, but in reality, these types of damage are indicators of a very common garden pest, Scale insects.
Scale are small insects, that look more like little bumps on the undersides of leaves than they do typical insects like aphids or whitefly. Most Scale live under a protective “shell” that is either a cottony, wax, or other firm substance as protection for themselves and the eggs. Males from a variety of species even develop wings and look like gnats around the plants. As for reproducing, females will lay their eggs under their protective covering, sometimes without even mating, and the eggs will hatch over a period of 2 to 3 weeks. Once these nymphs (or crawler) emerge, they move around the plant looking for a place to feed. This will typically only last a day or two, and once they settle, they begin to grow their protective covering.
Scale feeds using its straw like mouth parts to suck the sap or plant tissue out through the stems or leafs. This can cause stunting and reduced vigor, as well as dieback in some cases. The damage that scale causes is also a great indicator of what type of scale you might have on your trees or shrubs.
Soft Scale VS Armored Scale
Soft Scale, like Calico and Cottony Camellia Scale, are usually found on the undersides of the foliage and feed on the sap, but can also be found stems or along leaf veins. An easy indicator of soft scale is to look out for the honeydew (a sticky and shiny sugar) that the scale excretes which will drop onto the tops of leaves below, however you will probably notice the sooty mold that grows on the honeydew before you notice the honeydew itself. Because soft scale does not feed on chlorophyll, you should not see any signs of chlorosis, or yellowing on the leaves.
Armored scale on the other hand (e.g. Prunicola or White Peach Scale), can be seen on the twigs and stems, and by piercing the plant tissue on the stems, suck out the contents. Early damage signs of armored scale are yellowing of the leaves in the surrounding areas and in heavier infestations, defoliation and possible branch dieback. It is important to note that armor scale does not produce honeydew.
Nymph (Crawler) Stage- This will be the best time to spray for scale, however, this could prove challenging to the homeowners if they do not know what type of scale they have and may miss the already short window.
American Plant Recommends: Bonide®Neem-Oil- Spray top and bottom of the leaves in affected areas. Repeat every 10-14 days.
Plants near a fish pond? Substitute Organocide 3n1 Garden Spray, made with fish oils that will not harm fish.
Mature Scale- At this stage, most horticultural oils will not penetrate the scale’s protective covering so systemic insecticides are the most effective.
American Plant Recommends: ORTHO ®Tree & Shrub Insect Control- This granular treatment need only be applied once and will protect against scale and other garden pests for 10-12 months and also comes with a measuring cap for easy application. This should be applied around the drip line of the plant and be sure to pull away any mulch before application. Also available in 64oz concentrate.
Overwintering scales and eggs can also be controlled through the use horticultural oils like Neem-oil and Summit Horticultural Oil.
For more information on scale in our area, please visit
Landscape and Nursery IPM Alerts
Scale Commonly Encountered in Maryland Landscape and Nurseries
Common Scale in Maryland
Calico Scale (Eulecanium cerasorum) (soft scale)
Plants Damaged: dogwood, honeylocust, magnolia, maple, sweet gum, tuliptree and ornamental fruit trees.
Description: Adults are about the size of a pencil eraser. They are round and mottled white and dark brown to black. They are named after the calico pattern on their shell.
Monitoring: Look for copious amounts of honeydew in late May and early June. Look for the oval-shaped, yellow-bodied crawlers in June.
Crawler Stage: There is one generation a year. Early June through late September
Cottony Camellia/Taxus Scale (Pulvinaria occifera) (soft scale)
Plants Damaged: Taxus yews, camellia, holly, rhododendron, Japanese maple, English ivy, and mulberry
Description: These scales are cream to tan, elongated and flat. When females are producing eggs they create a white cottony ovisac that are two or more times their size.
Monitoring: Look for sooty mold and honeydew on the foliage. Examine the undersides of leaves for the white cotton-like sacs.
Crawler Stage: There is one generation a year. Crawlers begin to appear in mid-June.
White Prunicola Scale (Pseudaulacaspis prunicola)
Plants Damaged: Cherries, cherry laurels , magnolia, ligustrum (privets), rhododendron, forsythia, boxwood, and lilac.
Description: Females have a round, white body with orange to yellow center, like a fried egg. Males are more elongated and give bark a fluffy appearance.
Monitoring: Both male and female crawlers are salmon colored.
Crawler Stage: Three generation a year. First generation occurs in May. A second generation occurs in July and a third in September. Crawlers appear about 2 weeks earlier than white peach scale.
White Peach Scale Crawlers are out in early May to June. Second generation crawlers are out from mid-July to mid-August. The third generation crawlers are out in September.
Written by Wes Allen, Garden Supply Manager at 7405 River Road