Yucca Black Spots: Fungus, Bacteria, or Scale?

Two Likely Culprits

Progressive black spots moving upward with yellowing lower leaves suggest either:

1. Fungal/bacterial leaf spot from excess moisture
2. Scale insects (test: flick with knife—if removable, it's scale)

Treatment for Fungal/Bacterial

• Spray entire plant (leaf tops, bottoms, soil) every 3 days for 30 days
• Use Lysol or similar fungicidal/bactericidal spray
• Water correctly: Dry 4+ days between waterings
• Winter: Water monthly only

Treatment for Scale

• Remove visible scale with alcohol-dipped Q-tips
• Spray entire plant with 1 pint water + 1 quart rubbing alcohol + 1 tsp dish soap
• Every 3 days for 30 days (hatches continue 3 weeks)
• Rinse after alcohol treatment to protect foliage

Critical Watering Rule

Yuccas need EXTREME dryness between waterings. "Water, wait until dry, wait 4 MORE days, then water again." Overwatering enables both fungal growth and scale proliferation. Correct the watering, treat the specific problem consistently, and the plant recovers.