Diagnosing Black Bumps on Indoor Daisy Tree (Euryops)

A Colorado gardener brought their daisy tree (Euryops pectinatus) indoors for winter. The plant receives insufficient light, and now small, black, raised bumps appear on the limbs. The bumps haven't opened, and no insects are visible inside. The gardener wants to know if this is scale, a normal growth, or something else, and whether to treat preemptively.

Identifying the Problem

Two distinct issues can cause black bumps on Euryops:

Scale Insects

• Small, immobile bumps on stems and leaves
• Can be scraped off with fingernail
• Produce honeydew (sticky residue)
• Often accompanied by sooty mold (black fungal growth on honeydew)
• Treatment: Horticultural oil or neem oil, 2-3 applications 7-10 days apart

Botrytis Blight (Gray Mold)

• Fungal disease favored by cool, humid, low-light conditions
• Produces hard, black survival structures (sclerotia) on stems
• Also causes soft, brown blotches on leaves and stems
• Spores spread by air movement
• Treatment: Improve air circulation, increase light, reduce humidity, apply fungicide (chlorothalonil, copper, or neem oil)

Diagnosis for This Case

Given the description—black bumps that haven't opened, low light, humid indoor conditions, no visible insects—Botrytis blight is more likely than scale. The "black blisters" described match Botrytis sclerotia.

Immediate Actions

1. Prune affected stems back to healthy tissue. Sterilize pruners between cuts.
2. Improve environment: Move to sunniest location possible (south window). Add a small fan for air circulation.
3. Reduce watering: Water only when top inch of soil is dry. Avoid wetting foliage.
4. Apply fungicide: Neem oil or copper fungicide every 2 weeks through spring.
5. Monitor: If bumps are scale, horticultural oil will handle both issues.

Long-Term Care

Euryops needs full sun (6+ hours) to thrive. In Colorado winters, supplemental grow lights (12-14 hours daily) prevent the weak, disease-prone growth that invites Botrytis. Fertilize monthly with balanced fertilizer during active growth.