ENCLOSE a leaf of my very sick cabbage tree which is growing in
a pot. I've tried spraying it with Super Shield and also Malathion
without any success. The blight seems to be on every leaf and the
tree has had it for about four years. Is it terminal?
sample you sent had a serious infestation of cabbage tree scale.
These small insects suck sap from the leaves causing general debilitation
of the plant and lack of growth. Many cabbage trees are affected
by this scale but in the wild infestations are not usually so severe,
partly as the scale are partially controlled by natural predators
like ladybirds, but also because wild cabbage trees seem more resistant
to the scale than many of the modern hybrids. Growing cabbage trees
in containers also often leads to stress, through lack of water
or nutrients, which may make them more susceptible to attack.
The Malathion you used
should give quite good control but you'll probably have to apply
it three or four times at two to three week intervals, making sure
to get good coverage on both the upper and lower surfaces of the
foliage and allowing it to run down to the leaf bases and on to
the trunk. The dead scales often don't drop off for ages, so it
can sometimes be difficult to know if the spray has really worked.
Other products you could
use include oils like Super Spraying Oil, Conqueror and Eco-oil,
To keep the plant strong
and healthy, make sure the mix doesn't dry out excessively and fertilise
regularly during the growing season or repot into a larger container
with fresh mix.
Gardener, Issue 199, 2006, Page 29
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.