Bacterial Black Spot is a very serious disease of mangoes. In infected orchards, chemical disease control is difficult and on some farms 90% of fruit has had to be discarded.
Fortunately the disease has caused little damage in the Mareeba and Tablelands Mango growing areas, mainly because growers have been careful to obtain trees for planting from local sources known to be free of the disease. But growers are worried that the disease could be introduced by mango fanciers who are keen to import a particular mango variety and may get their trees from outside the district. If the variety you are looking for is not available locally or is in short supply this season, don’t risk infecting your property or the whole district by not being prepared to wait.
The disease organism is a bacteria, spread with planting material and during wet, windy conditions. Cyclones provide the perfect conditions for the disease to spread. On the leaves the bacteria causes black greasy spots. It looks different to the fungus spot, Anthracnose, as it is distinguished by the veins, so has an angular appearance. The fruit show the disease as black spots that enlarge, becoming irregular in shape, and the central part cracks to form a star.
If you have an infected tree or orchard the disease is difficult to control. Some steps to follow are:
1. Do not give away or sell bud wood or plants to anyone. This will only spread the disease problem, perhaps to our commercial orchards.
2. Establish good windbreaks. The disease seems much worse on trees affected by wind damage.
3. Prune trees so that foliage is not too dense nor limbs able to rub on each other. Tissue damage, even superficial, allows the bacteria to enter more readily. Sterilize pruning tools after pruning each tree.