Soft Scale Identification Guide

Soft Scale Identification Guide

Physical Characteristics

Soft scale insects belong to the family Coccidae. They look very different from what most people think of as bugs. Adult females show up as small, dome-shaped bumps on plant stems, branches, and leaves. They range from about 1 to 12 millimeters long. Most common species are between 2 and 7 millimeters.

Their soft, waxy coating is part of the insect’s body. This sets them apart from armored scale insects, which have a hard shell that can be peeled off. Colors change by species and life stage. You may see light tan, cream, dark brown, reddish-brown, or white (when cottony wax or egg sacs are present).

Adult females barely move once they settle on a plant. They have six tiny legs that shrink as they grow. They spend most of their life in one spot with their mouthparts pushed into plant tissue. Males are tiny winged insects that look like small gnats. They live only long enough to mate.

Common Species in North America

• Brown soft scale (Coccus hesperidum): One of the most widespread soft scales. Commonly found on houseplants and ornamental trees. Adults are yellowish-brown and flat, about 3 to 5 millimeters long.
• Tuliptree scale (Toumeyella liriodendri): A large species found on tulip poplars and magnolias across the eastern United States. Females reach about 6 millimeters and show mottled orange-brown coloring with dark markings.
• Cottony maple scale (Pulvinaria innumerabilis): Found on maples and other shade trees. Makes a white, cottony egg sac that can make branches look snow-covered in late spring.
• European fruit lecanium (Parthenolecanium corni): A common pest of fruit trees, oaks, and ornamental plants. Adults are shiny reddish-brown and strongly rounded.
• Wax scales (Ceroplastes spp.): Covered in thick, waxy coatings that give them a white or pinkish look. Found mainly in southern states on hollies, citrus, and other woody plants.

Soft Scale Behavior and Biology

Lifecycle and Reproduction

Soft scales go through these life stages: egg, crawler (first instar nymph), later nymph stages, and adult. Most species spend winter as young nymphs or adult females on bark and twigs. When spring warmth arrives, growth picks up again.

Females lay eggs beneath or behind their bodies, sometimes in a white cottony egg sac called an ovisac. One female can produce hundreds to thousands of eggs. When eggs hatch, tiny crawlers come out and move across the plant looking for a place to feed. This crawler stage lasts from a few days to about two weeks. It is the main way scales spread and the time when they are easiest to treat.

Once crawlers settle and start feeding, they move less and less with each molt. Many soft scale species can reproduce without mating. Some species have one generation per year. Others in warmer areas can have several generations each year.

Feeding and Honeydew Production

Soft scales feed only on plant sap. They push straw-like mouthparts into plant tissue to reach the phloem. Phloem sap has lots of sugar but not many other nutrients, so the insects have to drink large amounts. They release the extra sugar as honeydew, a sticky liquid that coats leaves, branches, and anything below infested plants.

Honeydew leads to two more problems. First, it feeds black sooty mold, a dark fungus that blocks light from reaching leaves. Second, it draws in ants, which guard the scales from predators. This ant-scale partnership often makes infestations grow worse over time.

Host Plants and Habitat

Soft scales attack many types of plants. Common targets include ornamental trees and shrubs, fruit trees, houseplants, and forest trees. You will find them on maples, oaks, tulip poplars, magnolias, hollies, citrus, ficus, and greenhouse plants. They settle on stems, branches, leaf undersides, and sometimes fruit.

Plants weakened by drought, poor soil, or other stress are more likely to suffer soft scale damage. In yards and landscapes, heavy infestations can build up after broad-spectrum sprays kill off the predators that normally keep scale numbers low.

Treatment Methods for Soft Scale

The key to soft scale control is timing treatments to the crawler stage, when the insects are most exposed and easiest to kill.

• Monitoring and timing: Good treatment starts with knowing when crawlers are active. Wrap double-sided tape around infested branches and check it often for tiny crawlers. Most species in cooler climates have crawlers from May through August. Tuliptree scale crawlers show up in September and October.

• Horticultural oils: Dormant oil sprays applied in late winter coat and smother scales on bare branches before leaves come out. Lighter summer-rate oils work well during crawler season. Make sure to cover stems and the undersides of branches fully.

• Insecticidal soaps: These contact sprays work well on soft-bodied crawlers. The soap must touch the insect directly to kill it and leaves no lasting residue. You may need to spray more than once as new crawlers hatch over several weeks.

• Predator management: Lady beetles, lacewing larvae, and parasitic wasps prey on soft scales. Targeted treatments that avoid broad-spectrum sprays help keep these predators around. Treating ant colonies near infested plants also helps, since ants shield scales from predators.

• Mechanical removal: On houseplants or lightly infested landscape plants, you can scrape scales off with a soft brush, your fingernail, or a cotton swab dipped in rubbing alcohol. Pruning badly infested branches removes large numbers of scales at once.

• Systemic treatments: For stubborn infestations on landscape trees, systemic insecticides applied as soil drenches or trunk injections provide long-lasting control. The plant absorbs the product and moves it through its tissues. Scales die when they feed on the treated plant. Always follow label directions and timing guidelines.

• Ant control: Ant bait stations or sticky bands around tree trunks cut off the ants that protect scale colonies. Without ant guards, predators can reach the scales more easily.

References

• Soft Scales (Trees & Shrubs) - University of Maryland Extension
• Scales - UC Statewide Integrated Pest Management Program
• Soft Scale Identification and Management on Ornamental Plants - NC State Extension
• Scale Insects - University of Minnesota Extension
• General Biology and Management of Soft Scale Insects - Journal of Integrated Pest Management
• Coccidae - Wikipedia