Rosemary Beetles
The rosemary beetle
The rosemary beetle (Chrysolina americana) is a smallish beetle, slightly larger than a ladybird. It has a metallic green body with purple stripes running from top to bottom.
The larva are a greyish colour and are similar in size to the adult beetle. The eggs are shaped like sausages and roughly the length of a pen tip. They may be found on the undersides of leaves from September until March.
The beetle is predominately a pest on rosemary and lavender plants, but it can also survive on sage and thyme. The beetle is mainly active in August to September, when it will feed and mate. Eggs will hatch after about two weeks, and the larva will feed for roughly three weeks before pupating underground. Due to the warmer winters, the beetle will overwinter on the plant.
What to do
The rosemary beetle can be controlled using either sprays or through picking off the adults and larvae. You can collect them using a newspaper placed under the plant, and then shaking or knocking the branches lightly to dislodge the insects.
Sprays should be used from August to late September, or in March to early May. Insecticides should not be used while plants are in flower because of the danger to bees. Only Provado Ultimate Bug Killer Ready to Use is approved for use on edible herbs.