Plant Doctor Archive

Cabbage tree scale

I 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?

THE 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, and Confidor.

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.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.