**Soft Scales** (Family Coccidae) are immobile, sap-sucking insects that infest trees and shrubs worldwide, including Magnolia, Maple, Tulip Poplar, and fruit trees. They are characterized by a smooth, often hemispherical wax covering that is **part of the insect’s body**. The conflict is severe and unsightly: they **suck phloem sap** (which is high in sugar), leading to tree stress, dieback, and massive excretion of **honeydew**, which in turn results in the growth of unsightly, black **sooty mold** over the entire plant and surrounding surfaces.
Taxonomy and Classification
Soft Scales belong to the order Hemiptera (True Bugs). They undergo simple metamorphosis. Unlike armored scales, soft scales have a soft, waxy, but non-removable protective covering and produce honeydew, making them highly attractive to ants and wasps.
Physical Description
Adult Scales are minute, 1/8 to 1/4 inch long.
- **Appearance (Key ID):** Smooth, dome-shaped, or helmet-shaped, often brown, yellow, or pinkish. They are immobile and fused to the branch.
- **Crawl Stage (Key ID):** The only mobile stage is the first instar nymph (the “crawler”), a tiny, flattened yellow insect active for a short period in the summer.
- **Damage Sign (Key ID):**
- **Honeydew:** Visible, sticky, clear residue coating leaves and branches.
- **Sooty Mold:** Black, velvety fungus growing on the honeydew.
- **Branch Dieback:** Yellowing leaves, defoliation, and dead twigs (due to heavy sap loss).
- **Conflict:** Severe plant stress, aesthetic loss, and fungal growth.
Distribution and Habitat
Soft Scales are cosmopolitan. Their habitat is the bark of young twigs, small branches, and occasionally the undersides of leaves of ornamental and fruit trees.
Behavior and Conflict
The conflict is systemic stress and fungal contamination.
- **Sap Depletion:** Continual sucking of phloem sap leads to severe resource depletion in the host plant, resulting in significant growth loss and canopy thinning.
- **Sooty Mold:** The mold is not parasitic but grows so densely that it shades the leaves, reducing the plant’s ability to photosynthesize.
- **Ant Protection:** Ants aggressively protect soft scales from natural enemies (like parasitic wasps and lady beetles) to maintain the honeydew food source, making biocontrol difficult.
Management and Prevention
Control is integrated pest management (IPM), with precise timing for chemical intervention.
- **Dormant Oil:** Apply a heavy-weight horticultural oil during the late winter/early spring dormant season to smother overwintering nymphs on the twigs.
- **Crawler Spray:** Apply a residual insecticide when the vulnerable crawler stage is active (timing determined by monitoring, often late spring/early summer).
- **Systemic:** A systemic soil drench applied in the spring can be highly effective, as the insecticide is moved into the phloem tissue where the scale feeds.
- Control ants near the base of the tree with granular baits to allow natural enemies to attack the scale population.
Conservation and Research
Soft Scales are managed as major landscape and nursery pests. Research focuses on optimizing systemic insecticide uptake, timing crawler emergence for better control, and promoting the use of specialist parasitic wasps for biocontrol.