Plant Doctor Archive

Sick cabbage tree

We have a very large, old cabbage tree and it is shedding more than the usual amount of leaves. There are about 10 or so 'heads' of leaves, a couple of which are now stumps with no leaves at all and have turned sort of spongy. There was a caterpillar type thing on it a while ago, but I sprayed it and now the new shoots are coming without holes in, so I think I have killed that particular bug. It flowered in summer, and someone said the excessive shedding may just be the time of year. I have heard of the dreaded 'cabbage tree disease' — could this be it?

Unfortunately it sounds as if your cabbage tree has the 'cabbage tree virus'. There is little that can be done to save it. If you cut the cabbage tree down to ground level there is a good chance it may regenerate.

The signs of the disease are dieback, yellowing of old leaves, and the collapse of the crown.

The disease was first noticed in the mid 1980s. There are several theories regarding the rapid decline of cabbage trees. Some think that it is related to the high UV light experienced in New Zealand.

One nurseryman comments that in a nursery situation, if trees are well watered, fertilised and flowers cut off, they stop dying. The same nurseryman also noticed that trees are not dying in the South Island like they are in the North Island because they have evolved under higher UV light.

Scientists have found the presence of a parasitic bacteria, Candidatus Phytoplasma australiense, which is believed to be spread by the Australian Passionvine Hopper. Research shows that the disease is similar to the yellow flax disease which lead to the collapse of New Zealand's flourishing flax fibre industry early last century.

The good news it that the disease is not spreading as rapidly as it was, and Landcare Research and HortResearch scientists are looking at ways to manage the disease long-term.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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