Garden Pests: The Rosemary Leaf Beetle

Shining like a small purple striped emerald gem, the Rosemary Leaf Beetle is causing alarm to Britain’s gardeners. A native of warmer climates, the beetle was first noticed within the British Isles in 1994, and with no natural predators, has continued its march across the country. Stripping plants of their growing tips, beetles and grubs alike, can cause serious damage to Rosemary and Lavender whilst also able to grow on other herbs such as Sage and Thyme.

Laying their eggs on host plants in the late summer months of August and September, the grubs hatch after only two weeks and begin feeding. Growing to between five and eight millimetres, the greyish white grubs disappear into the soil to pupate after only two to three weeks, only to re-emerge another two weeks later as fully developed adults. Their fast life cycle means that any small colony can soon become a large mass of herb stripping pests which can put pay to most host plants, whereupon they’ll move on to the next available food source.

Docile and inactive on the host plants between June and August, these pests can often be confused for an attractive and innocent garden addition, but the damage to plants that they can be responsible for cannot be avoided. If possible, insecticides should not be used due to their dangerous effect to other, garden friendly species such as bee’s, ladybirds and butterflies. Lavenders and other similar species are a high nectar content plant and thus are a huge attraction for garden aiding species. Measuring approximately 8mm, adult beetles can easily be handpicked off of the host plant and discarded, along with their grubs which may be found on the underside of leaves. Continuous and careful stripping of this pest will help to keep pest numbers to a minimum.