Pest
Rosemary beetle
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in January | Watch for in February | Watch for in March | Watch for in April | Watch for in May | Watch for in August | Watch for in September | Watch for in October | Watch for in November | Watch for in December |
What it is
Rosemary beetle is a small, beautiful leaf beetle, about 8 mm long, with metallic green and purple stripes along its back. Native to southern Europe, it was first found breeding in Britain in the 1990s and is now common in southern England and spreading. It feeds on aromatic shrubs and herbs in the mint family.
Symptoms
Adults and larvae chew the foliage, and shoot tips may turn brown and dry out where leaves have been eaten. The larvae are soft, greyish white grubs with darker stripes, living among the needles. Look for dark droppings and the beetles themselves, which are easiest to find on mild days. Damage is mostly cosmetic on large plants, but small or young plants can be badly checked.
Cause
Unusually, this beetle is most active in the cooler months. Adults are present all year but rest in summer, then lay eggs from late summer onwards. Eggs, larvae and adults can all be found from autumn to spring, with larvae feeding before dropping into the soil to pupate.
Control
Hold a sheet of newspaper or an upturned umbrella beneath the plant and tap the stems sharply; beetles and larvae fall out and can be destroyed. Repeat every week or so through autumn, winter and spring. Squash eggs and grubs you find by hand. Avoid insecticides on herbs you plan to eat, and on lavender and rosemary in flower because they are so popular with bees.
Prevention
Check new plants carefully, as the beetle often arrives on nursery stock. Keep an eye on sage and thyme planted nearby. Healthy, well-grown shrubs in sunny, well-drained spots tolerate damage best, so trim lightly after flowering to keep growth dense.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: January, February, March, April, May, August, September, October, November and December.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.