Fungal Leaf Spot (Latin name varies depending on species)

Plants/trees Affected

All commonly grown trees & shrubs

Symptoms

The appearance of brown, tan or black blotches on leaves, followed by defoliation.  Leaf spots can vary in size from that of a pin head to those which almost cover the whole of the leaf.

Causes

Leaf spots can be caused by insects, air pollutants and bacteria but are more likely to be the result of infection by a pathogenic fungi.  The fungi live on fallen leaves through the winter and in spring spores will be discharged and carried by the wind or rain to the new leaves.

The spore combined with water on the leaf allows the fungus to germinate and penetrate the leaf causing infection.  As the fungus develops the spots will appear and it may also lead to other types of fungi and secondary infections developing.

Prevention

The majority of trees and shrubs will survive an attack of Fungal Leaf Spot and it will not be fatal unless there are other underlying problems which have left the plant in a weakened condition.  By the time the leaf spots appear it is too late to apply a chemical control, any treatment of this nature must be applied before the spores penetrate the leaves.

To successfully defeat leaf spot you must spray the tree/shrub with a fungicide in early spring at ‘bud break’, again in 7-14 days and a third application if there has been frequent rainfall.  In addition it may help to rake and destroy old fallen leaves removing the opportunity for spores to over winter in the immediate area but  as spores can travel vast distances it will not prevent an outbreak of the disease altogether.  Refraining from overhead watering and increasing the air circulation around woody shrubs will also help with prevention of the disease.

 
Treatment

Once the leaf spots appear it is usually too late to apply a chemical control for the current season and would only be necessary if the tree/shrub is already in a weakened state.

There are limited fungicides available to treat this condition but fungicides such as Bio Systhane Fungus Fighter and Scotts Fungus Clear which are labelled for the control of other diseases may give some control of the fungal leaf spots. They will however have no effect against the bacterial leaf spot.