Rosemary beetle
A 7mm beetle with metallic green and purple stripes, feeding with its grey grubs on the foliage and flowers of rosemary, lavender, sage and thyme. It is unmistakable once seen and it is missed constantly, because its main feeding period runs from late summer right through the winter — the months when nobody is looking for a pest, and when the damage on an evergreen herb is put down to cold or wet instead.
Caused by: Chrysolina americana · also called striped beetle on rosemary, lavender beetle
What brings it on
Established across most of Britain since the 1990s and spreading north. Adults and larvae both feed on the foliage, and the population peaks between late summer and spring rather than in the growing season, which is why a rosemary that thinned over winter is so often diagnosed as cold damage.
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Sourced guidancehigh confidence
- Royal Horticultural Society: Rosemary beetle
- Agriculture and Horticulture Development Board — AHDB: Ornamental Lamiaceae pests
Checked 2026-08-13
Usually seen: August, September, October, November, March, April
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Look at the plant in autumn and winter, which is the habit this pest depends on nobody having. Shaking a branch over a sheet of paper takes ten seconds and settles the question for the whole plant.
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Horticultural consensusmoderate confidence
- Royal Horticultural Society: Rosemary beetle — control
Checked 2026-08-13
Dealing with it once it is there
- Shake the plant over a sheet of paper or an upturned umbrella and collect what falls — beetles drop rather than fly when disturbed, so this collects most of a population in one pass, and repeating it every few weeks through the winter keeps a herb you are going to eat entirely free of treatment.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Rosemary beetle — control
Checked 2026-08-13
- Do not spray a culinary herb for this. The damage is cosmetic on an established plant, the beetle is active in the months when the herb is least used, and hand-collection genuinely works — which is not something that can be said of most pests.
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GrowingHQ editorial positionhigh confidence
A proportionality judgement about an edible crop rather than a horticultural claim, and the reason the action field leads with a sheet of paper.
- GrowingHQ editorial synthesis — GrowingHQ
Checked 2026-08-13
What it affects
On sprays and treatments
GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.