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vendredi 17 juin 2011

Lovely but nasty.

 Today I'm going to talk to you about what I call a "lovely but nasty" bug : the Rosemary Beetle (Chrysolina americana).

Rosemary Leaf Beetle - Picture : web

Lovely indeed : look at those magnificent metallised little bugs. Aren't they cute?! They are 8mm long and have metallic green wings with iridescent purple lines.

But nasty : they will devour your rosemary leaves in a heartbeat. And then your lavender, your thyme and your sage too.

Their larvae are grey with darker stripes and are up to 8mm in length.

They were first spotted in England at Wisley Garden, Surrey, in 1994, but didn't became a problem before 2005 when they decided to widespread across the south-east part of England. They now are one of the top 10 most frequent pest enquiries made to the RHS Members’ Advisory Service !

The adults start to be particulary active on their host plants during late August and September : they feed, mate and lay eggs until next spring. The eggs hatch within two weeks and the larvae feed for three weeks before entering the soil to pupate. The pupal stage lasts for two to three weeks before adults emerge.
And then the cycle begins again! 

Rosemary Beetle - Picture : web

There are different ways of getting rid of them :
  • You can handpick them and ... well ... you know... dispose of them. The best time to do it is before the end of summer.
Here's a good tip from the RHS (Royal Horticultural Society) : open upside down an umbrella under the branches and tap the plants to dislodge the insects.
  • You can use a homemade solution made of 1/3 of soap and 2/3 lemon juice that you spray on the little devils.
  • You can use pyrethrum-based insecticides. But, as you usually find these insects on aromatic herbs (rosemary, sage, thyme,...), it's best to avoid insecticides and stick to the lemon juice/soap solution. If you really want to apply insecticides, you should not do it when plants are in bloom as these are harmful to bees and others pollinating wildlife.
One last thing : be sure that you're dealing with the Rosemary Beetle ! Its cousin, Chrysolina cerealis or Rainbow leaf beetle, is quite similar BUT it's a protected specie in the UK.

Chrysolina cerealis - Picture : Michel Ehrhardt
How to differenciate them? The green part of the Rosemary beetle's wings are "hammered". 

So keep your eyes open and if required, use your umbrella (once again!).

1 commentaire:

  1. There it is! This is the beast that invaded my lovely lavender bush!
    Many thanks for the tips