albizzia has grubs in the branches. They bore through the centre
and the branches appear to be bleeding. What can I do?
HATE to say it but it sounds like the native insect known as lemon-tree
borer has attacked your poor albizzia. It's a beetle that evolved
among native plants but has taken a liking to many of the exotics
we now grow in our gardens. Over the years it has caused extensive
damage to citrus trees, hence its common name, but it can attack
a wide range of ornamentals.
The adult beetle is quite
common in spring and summer, flies at night and lays its eggs in
the bark of susceptible trees. The larva hatches, bores into the
branch and burrows along its length, creating tunnels that can weaken
the branch and may eventually kill it. Badly affected trees can
lose so many branches that the tree is weakened and total removal
is the only option. The good news is many trees can survive quite
happily with some borer damage and may recover to live long, fruitful
It's virtually impossible
to control borer with sprays. Some claim you can kill the grubs
by poking fine wires into the holes or injecting insecticide in
with a syringe, but I've always found that harder than it sounds
- just finding the entry points is a challenge. I suggest as soon
as you see signs of borer damage, you prune off as many of the affected
branches as practicable. Make sure to cut well past where the borer
has travelled - if you see borer tunnels in the branches cut back
into solid healthy wood.
The female beetle may
be attracted to fresh bark wounds, so an application of pruning
paste to the cut surfaces could help. Try using Bacseal Pruning
Paste which may create a physical barrier to deter the beetle from
laying eggs around fresh pruning wounds.
Gardener, Issue 204, 2006, Page 38
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.