Scale Insects on Mulberry: Dormant Oil Treatment

Diagnosis: Not Fungus, But Insects

White, rice-grain-like bumps on dormant mulberry bark in southern Georgia are scale insects—most likely white peach scale (Pseudaulacaspis pentagona) or mulberry scale. These armored scales overwinter as immobile adults under protective covers, appearing as stationary white flecks. They're not powdery mildew, moss, or mold.

Why Dormant Season Treatment Works Best

Armored scales are nearly impervious to contact insecticides once their waxy covers form. However, during winter dormancy:

• Deciduous hosts lack foliage, ensuring thorough spray coverage
• Scales are in vulnerable overwintering stages
• Beneficial insects are less active, reducing non-target effects
• Lower temperatures reduce phytotoxicity risk

Dormant Oil Application Protocol

1. Product: Horticultural/dormant oil (paraffinic mineral oil, 97%+ purity). Common brands: Volck, SunSpray, Bonide All Seasons.
2. Timing: Apply when temperatures will remain 40–85°F (4–29°C) for 24+ hours. Late winter (February–March in Georgia) before bud swell is ideal.
3. Coverage: Spray to runoff—every bark surface, branch crotch, and twig. Use a pump sprayer with coarse droplet setting.
4. Repeat: A second application 2–3 weeks later catches late hatchers.

Season-Long Monitoring

In spring, crawlers (mobile nymphs) emerge—this is the only stage vulnerable to contact sprays. Monitor with double-sided tape on branches; when crawlers appear, apply insecticidal soap, neem oil, or horticultural oil (summer rate: 1–2%). Systemic dinotefuran (Safari) or imidacloprid (where labeled) provides season-long control but check pollinator restrictions.

Cultural Support

• Prune heavily infested branches
• Improve air circulation via thinning cuts
• Avoid excess nitrogen (promotes succulent growth scales prefer)
• Encourage predators: lady beetles, parasitic wasps (Aphytis, Encarsia)

Prognosis

Mulberries tolerate moderate scale pressure. Consistent dormant oils + spring crawler management typically reduce populations below damaging thresholds within 1–2 seasons.