Spots or pest damage can follow spider mites in dry indoor air. Outdoors, consider rosemary beetle, leafhopper, scale, and tortrix. Other possibilities include powdery mildew, root rots, and overwatering-related browning or leaf drop.
Rosemary pests and spots
Check both leaf surfaces, stems, and the root zone before treating. Rosmarinus officinalis can show pest or spot problems that depend on whether the plant is indoors or outdoors.
Check the leaves, stems and pot
Look for pests or spreading spots
Record stippling or bronzing, webbing, sticky residue, scale-like bumps, powdery growth, discrete spots, browning, or leaf drop on Rosmarinus officinalis. Note whether damage is on new or older growth.
Inspect leaf undersides and stems for spider mites, scale, leafhoppers, or beetle damage. Check root-zone condition, drainage, airflow, indoor humidity, recent moves, and whether the plant is in an outdoor container.
Use the visible signs to choose the next check
What the signs may mean
If insects are visible, isolate the pot and inspect the whole plant. Correct a persistently wet root zone, improve airflow and light, and use only a treatment labeled for the plant and setting. Remove badly damaged material only when it is clearly dead or infested.
Watch for new damage or recovery
What to check again
Recheck both leaf surfaces, stems, root-zone condition, and new growth after the environment has been stable. Compare whether fresh damage is still appearing instead of expecting marked leaves to turn normal.
Do not diagnose from one sign alone
What visible signs cannot tell you
Sources
- Royal Botanic Gardens, Kew: Plants of the World OnlineTaxonomy; accepted name; included synonym; native range; cultivation
- Royal Botanic Gardens, Kew: Plants of the World OnlineName status; synonymy to Salvia rosmarinus
- Royal Horticultural SocietyGetting started; Sun; warmth; free-draining soil; containers; winter protection
- Royal Horticultural SocietySynonyms; Position; Growing Conditions; Pests; Diseases
- University of Maryland Extension / Ask ExtensionExpert Response; indoor rosemary guidance
- Iowa State University Extension and OutreachBest Herbs for Indoors; The Best Growing Conditions for Indoor Herbs