Hi, our lemon tree has some blackish leaves & white lumps on the fruit skins as well as on some of the branches. What can I do about this. Regards Heather.

Hi Heather, your tree has an infestation of scale insect which are sap sucking insects that excretes honey dew as it feeds. The black substance is sooty mould which is an air-borne fungus that feeds on the honey dew. If you scrape one of the small bumps there will be an insect inside. There may also be ants crawling amongst the trees, which are also feeding on the honey dew. If you eliminate the insects you will get rid of the sooty mould. Horticultural or orchard (conqueror) spraying oil should be enough to control scale insect, make sure you get it inside the canopy and repeat sprays will be necessary. Talk to your local garden centre or hardware store for a suitable control as there are other insecticides that will eliminate scale insect, such as a pyrethrum based spray. The Sooty mould looks unsightly and won't harm the tree, it does reduce growth and plant vigour, as do the insect pests that are causing the problem. The fruit will be okay to eat, they just look unsightly. Residual sooty mould can be removed by spraying with (conqueror) oil, the mould eventually washes off with water or rain. Consider thinning out the centre of your tree to improve air circulation, remove weak spindly growth and branches that crisscross each other. Lianne