just found a pile of sawdust at the base of one of my best-loved
roses, where a weevil has bored into the bush through a dead branch.
I know my lemon tree, two metres away, has this weevil and we've
lost a camellia the same way. Can I save this rose and lemon tree,
or is it too late? The hole goes in some way on a downward angle.
sounds like a simple case of lemon tree borer, a native beetle that
attacks quite a wide range of trees and shrubs. The female beetles
lays eggs in spring and the larvae hatch out and bore into branches
then spend up to the next two years boring tunnels, feeding and
growing larger before pupating and finally emerging as adult beetles.
The sawdust you spotted are remains of the wood that has passed
through the borer and been discarded from its tunnel.
Borer can be difficult
to control as they're quite well protected inside their tunnel.
Rose expert Doug Bone suggests you cut back the affected branches
until you reach solid wood with no sign of tunnelling. You can cut
every shoot off a badly affected rose bush and it will usually recover.
If you spot damage on
the lemon tree early enough you can sometimes kill the borer by
poking a thin wire into the tunnel or squirting kerosene or insecticide
into it with a syringe, otherwise cut back the damaged branches
to healthy wood. Unless they're severely attacked, lemon trees can
often last for years with some borer damage.
Gardener, Issue 183, 2005, Page 31
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.