The magnolia scale, about 1/2 inch in diameter, is a soft scale that feeds on magnolias. Undetected infestations steal sap and vigor from landscape trees while covering foliage with honeydew and the resulting sooty mold. Heavily infested trees (Figure 1) can suffer branch dieback or even die.
Mature female scales appear in late summer as pink-orange bumps covered with white waxy powder.
Each one produces a batch of eggs that hatch in late summer. Tiny crawlers settle on branches and remain there during winter. Later nymphal stages are dark gray with a reddish brown ridge along the middle of their backs. Development resumes the following spring to complete the single generation that occurs each year.
Controlling soft scales can be challenging and may require a combination of measures over several seasons.
- Cultural – Reduce stress on infested plants by watering as needed; do not fertilize excessively.
- Physical – If practical, remove heavily infested branches or gently scrub infested areas with a soft brush and soapy water to remove as many females as possible before egg hatch.
- Dormant oil – Apply dormant oil to overwintering nymphs during early spring, but before buds open. This is a contact spray, so thorough coverage is needed for good results.
- Insecticides – Sprays of insecticidal soaps, horticultural oils, or insecticide sprays also can be directed at crawlers during late summer. Proper timing of insecticide applications is a major key to success. Applications must target newly hatched scale crawlers, which are very susceptible to control measures while moving over plant surfaces to find a feeding spot. Once settled, crawlers begin to secrete a waxy covering that shields them from sprays. Systemic insecticides containing either imidacloprid or dinetofuran can be applied as a soil drench several weeks before crawlers become active.
By Lee Townsend, Extension Entomologist