robinia - 1
PLANTED a Robinia 'Frisia' about 10 years ago which grew
really well and looked a picture every summer until a couple of
years ago. Last summer several branches hardly grew any leaves.
Now they look dead and brittle. From what I've heard, these symptoms
sound a bit like root disease. Have you any tips that might help
more likely your robinia has been attacked by lemon tree borer.
The borer is a native beetle that lays its eggs in quite a range
of trees, including robinias and citrus. The female beetle lays
eggs in spring and the larvae hatches out and bores into branches,
then spends up to the next two years boring tunnels, feeding and
growing larger before pupating and finally emerging as an adult
beetle. Some tunnels open to the outside. If you look carefully
you may find these openings with tell-tale droppings coming out.
The damage the borer
causes can result in whole branches gradually dying. Unfortunately,
there's no easy way to control them. Prune out all the branches
that look as if they're affected, cutting back to healthy wood.
Burn them or put them through a chipper to kill the larvae. You
can try poking thin wire down the tunnels in an attempt to kill
them or squirt kerosene into the holes with a syringe, but neither
method has a high likelihood of success.
Fertilise the tree well
and water in summer to encourage new growth which, with luck, will
stay free of borer.
Gardener, Issue 157, 2004, Page 30
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.