Prickly Pear Brown Spots: Scale Insect or Fungus

Two Likely Culprits

3-year-old Opuntia in Phoenix, transplanted 2 weeks ago, small brown rust-like spots.

1. Scale Insect

• White when dry, red when wet (cochineal dye source).
• Hard to eradicate – scrape off manually, then spray horticultural oil.
• Systemic imidacloprid works but affects pollinators.

2. Fungal Rust

• True rust fungi rare on Opuntia; more likely Alternaria or Colletotrichum (anthracnose).
• Copper fungicide or chlorothalonil (Daconil) per label.
• Improve air flow; avoid overhead water.

Diagnosis

Scrape a spot: if it smears red = scale. If powdery = fungus. Photo to gregandkat@msn.com confirms.

Transplant Stress

Recent move may have triggered latent issue. Water sparingly during establishment.