Sunburn = bleached white/tan patches on sun-exposed sides. Tiny brown spots on all leaves (including shaded) suggest sucking insects (aphids, mealybugs, spider mites) that fed before move.
Dark/red pigments (anthocyanins) in 'Zwartkop' etc. may deter insects or mask damage. Green tissue is more palatable.
Hydrangea Leaf Spots: Cercospora vs. Anthracnose Identification
Baseball Plant (Euphorbia obesa) Problems: Brown Spots and Etiolation
Tall Cactus With Leaves? It's Likely a Euphorbia
Stanhopea Leaf Spots: Sunburn vs. Fungal Infection
Brown Spots on All Rose Leaves: Weather Stress vs. Fungal Disease
Hydrangea Leaf Spots: Injury vs. Cercospora Re-evaluation
Indoor Lemon Tree Losing Leaves: Fungus and Possible Spider Mites
Arborvitae Brown Patches: Abiotic or Fungal Twig Blight
Fungus Gnat Control: Target the Larvae, Not the Flies
Brown Flower Spike on Gift Orchid: Normal Dieback
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