Rosemary beetle

The rosemary beetle (Chrysolina americana) originates from southern Europe and has been found in Britain since the mid-1990s. The larvae and adults feed on the foliage of rosemary and related plants.

Rosemary beetle

Rosemary beetle

Quick facts

Common name Rosemary beetle
Scientific name Chrysolina americana
Plants affected Rosemary, lavender, sage, thyme and some other related plants
Main symptoms Foliage eaten where beetles and grubs have been feeding
Most active August-April; adult beetles present throughout the year

What is rosemary beetle?

Rosemary beetle is an insect that eats the foliage and flowers of various aromatic plants, such as rosemary, lavender, sage, thyme and some other related plants.

Rosemary beetle has spread rapidly since first being found breeding in central London. It is now widespread throughout England and Wales. It is established in Scotland, present on Northern Ireland and may be established in parts of the Republic of Ireland.

Both the adult beetles and the larvae feed on the foliage and flowers of host plants, with most of the damage occurring between late summer and the spring. Heavily infested plants can look very shabby by spring. The plants' appearance will usually improve as new growth develops in late spring-summer. 

Survey

Seen the rosemary beetle? We would like to know.

As part of RHS research we would like to know where the rosemary beetle has been seen.

Please submit your records via our rosemary beetle survey (expected time to complete survey = two minutes).
The RHS confirms that your information will be stored in compliance with the Data Protection Act and personal data will not be shared with third parties. If you prefer not to have your information used in this way, please indicate when submitting your record.

Thank you to everyone who has submitted records – read a blog about the surveys

Watch an animated map of the results from the Rosemary beetle survey (links to YouTube)

Symptoms

Rosemary beetle and its damage are fairly easy to spot;

  • The adult beetles are shiny insects, 6-7mm long, with metallic purple and green stripes on their wing cases and thorax
  • The larvae are greyish-white with darker stripes running along their bodies; when fully grown the larvae are 8mm long
  • Both the adult beetles and the larvae feed on the leaves, which can be reduced to short stumps with greyish-brown discoloration where the damaged tissues have dried up
  • The flowers can also be damaged

Control

 

Host plants can survive light infestations without any noticeable adverse affects and so control is not always necessary

Non-chemical control

Hand picking can help to keep infestations below the level at which serious damage occurs. With the taller forms of rosemary and lavender, the beetles and larvae can be collected by tapping or shaking the branches over newspaper spread underneath the plant.

Chemical control

  • Pesticides are likely to be more effective on larvae than adults
  • Heavy infestations which are impractical to remove by hand can be treated with pesticides
  • If the plants are being used for culinary purposes, herbs must be listed on the product label and the manufacturer’s instructions must be followed, particularly the harvest interval that needs to be left between treatment and using the leaves
  • Organic insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit or Defenders Bug Killer, ecofective Bug Killer (also contains fatty acids)). Several application of these short persistence products may be necessary to give good control
  • Synthetic pyrethroid pesticides such as lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), or deltamethrin (e.g. Sprayday Greenfly Killer) can be used
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) can also be used 
  • Plants in flower should not be sprayed due to the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

During mid-summer rosemary beetle can be present on host plants as adult beetles that usually do little or no feeding. In late summer they commence feeding, mating and laying eggs. These hatch after about ten days and both adults and larvae will feed on the foliage throughout autumn to spring during periods of mild weather.

When fully fed, the larvae go into the soil to pupate. Adult rosemary beetles emerge from pupae in the soil in early summer. There is one generation a year but because the adults are long-lived, there can be some overlap between the new and old generations of adult beetles. Because of this, adult beetles can be found at almost any time of year.


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