Chrysolina americana is a pretty leaf beetle commonly found on Rosemary. Their attractive colouring makes them easy to spot, especially on a sunny day! They're mild to moderate pests of Rosemary and other woody, herbaceous plants. Activity is at its highest in late summer and spring. It's advised to check plants for adult beetles regularly, and year-round. Brown, wilted plant tips in Rosemary, Thyme, Sage and Lavender should prompt a gardener to inspect plants more closely!
Can strip foliage if in high abundance.
Predated by other garden animals.
Adult: Mature beetles are shiny metallic insects measuring roughly half a centimetre. They are colourful, boasting purple and green stripes running along the length of their thorax and wing cases. Larvae: The larvae are coloured grey-white with darker stripes on the body. At full size, they measure just below a centimetre. Pupae: Currently unavailable. Eggs: Tiny, sausage-shaped dark red-brown eggs may be found in clusters at the end of herb branches.
Holes in leaves and flowers. Brown, dried-out plant tips. Stunted growth. Brown-grey grubs with black on branches. Stripey, metallic beetles on branches. Sausage-shaped eggs may be found at the end of branches beneath leaves.
Europe, Britain and Israel
Control is not always required; mild infestations do not dramatically harm the host plant species. Smaller plants are more at risk. Hand-picking of the insects as they appear can maintain rosemary beetle populations at a manageable level. Searching with a flashlight in the dark is ideal as their metallic bodies reflect light, making them easier to detect. For taller host plant species, place fabric or paper below the infected plant, then tap or shake the branches and quickly collect the beetles underneath. Grub larvae can be collected by running kitchen towel gently over the branches of plants. Attract garden birds into your green spaces using feeders, tables, perching spots and baths.
Pesticides are recommended for heavy infestations that can't be controlled from hand-picking. Chemical control should always be used as a last resort. Take care with chemical control if the plant is used intended for eating. Some chemical treatments for Rosemary beetle include organic insecticides with natural pyrethrins. Several applications may be required for full control. Synthetic pyrethroid pesticides, such as deltamethrin or lambda-cyhalothrin, can be used as the final attempt to remove the pests. Please note* Thyme, lavender, sage and rosemary are all favoured by bee and hoverfly pollinators, so please take care if you are planning to spray your plants. We don't advise applications of pesticides when flowers are present. Always read instructions and make sure your plant is listed on the bottle if you intend to eat it.
Plants in the mint family, Lamiaceae.