Troubleshooting
Arp Rosemary problems — and how to fix them
Arp Rosemary (Rosmarinus officinalis 'Arp') is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Root rot (Phytophthora, Pythium)
The most frequent killer. Caused by waterlogged soil or pots without drainage holes. Symptoms include wilting despite moist soil, blackened stems at the base, and foliage that turns brown from the bottom up. Improve drainage immediately and reduce watering frequency.
Powdery mildew
White, powdery coating on foliage, especially in humid, still air. Increase spacing, improve airflow, and avoid wetting foliage. Affected branches can be pruned out; severe cases respond to a bicarbonate or sulfur-based fungicide spray.
Spittlebug (froghopper)
Frothy white 'cuckoo spit' masses on stems in late spring to summer, produced by nymph feeding. Rarely causes serious damage on established shrubs. Remove by hand or dislodge with a strong water jet; chemical control is rarely warranted.
Prevent arp rosemary problems before they start
Most arp rosemary issues are care-mismatch, not bad luck. Dial in the basics:
- Common rosemary problems — the species this cultivar belongs to
- Common arp rosemary problems — our other guide for the same plant
- What's wrong with my plant? — the diagnosis apps compared
- Arp Rosemary watering schedule
- Arp Rosemary light requirements
- Best soil mix for arp rosemary
- Arp Rosemary temperature & humidity
- Full arp rosemary care guide
Looking for the species overview? Rosemary — the full care guide.
Other Rosemary varieties
Arp Rosemary problems — FAQ
Why is my arp rosemary root rot (phytophthora, pythium)?
The most frequent killer. Caused by waterlogged soil or pots without drainage holes. Symptoms include wilting despite moist soil, blackened stems at the base, and foliage that turns brown from the bottom up. Improve drainage immediately and reduce watering frequency.
Why is my arp rosemary powdery mildew?
White, powdery coating on foliage, especially in humid, still air. Increase spacing, improve airflow, and avoid wetting foliage. Affected branches can be pruned out; severe cases respond to a bicarbonate or sulfur-based fungicide spray.
Why is my arp rosemary spittlebug (froghopper)?
Frothy white 'cuckoo spit' masses on stems in late spring to summer, produced by nymph feeding. Rarely causes serious damage on established shrubs. Remove by hand or dislodge with a strong water jet; chemical control is rarely warranted.