There are more than 700 different types of eucalyptus trees.The eucalyptus belongs to the family myrtaceae and is usually a very hardy, insecticidal tree in nature, but it does have a few common problems with disease. When disease strikes the eucalyptus, it can wipe out a single tree or spread to an entire plantation or forest area, depending on the type of disease.
Eucalyptus Rust (Puccina psidii), or guava rust, is the only rust disease that attacks the eucalyptus tree. This is a serious disease that attacks young shoots, cuttings, seedlings or a mature tree that has sustained damage. This disease causes deformed leaves leading to defoliation and stunted growth. This disease often kills eucalyptus trees.
Eucalyptus rust is spread through spores. People who work or visit places where the eucalyptus tree has rust should thoroughly clean their clothes so they do not spread this disease elsewhere. The first signs of eucalyptus rust are tiny raised spots on infected areas. These areas turn the colour of egg yolks in a few days.
Canker disease is caused by the Chrysoporthe cubensia mushroom, and it infects the bark and cambium of the eucalyptus tree first. Cankers are sunken necrotic lesions. When a tree branch is infected with canker, the leaves turn yellow or brown and wilts. The leaves undergo a process of defoliation called Mycosphaerellas. If not treated, the canker can girdle the entire branch, killing the limb or even the entire tree.
Anthracnose, or twig blight, kills the branches and twigs of the eucalyptus tree. The symptoms of this disease vary depending on the weather and time of year that it occurs. Some symptoms include leaves that shrivel and curl. The leaves may also have sunken lesions on the stems. Control this disease by raking and destroying the fallen leaves and twigs as they fall during the seasons. During the winter, prune away infected twigs and branches. Pruning during the winter months also improves air circulation in the canopy, helping to prevent this disease from spreading.
Phytophthora fungi is a name for root, collar, foot and crown rot. The symptoms of this disease are discoloured leaves that become stunted and drop easly. If you peel away the bark of the eucalyptus tree, you may notice that the trunk has turned cinnamon brown or a dark grey colour, and it may ooze with black or reddish sap. The growth of an infected eucalyptus tree will slow and gradually diminish.
Powdery mildew is a disease that is easily recognisable because it looks like white powder on top of the leaves of the eucalyptus tree. This disease can distort new limbs or stunt the tree's growth. When infected plants have this disease, the infected leaves will drop before they should. Plant the tree where it will receive full sun, and do not spray the leaves when you water.
Heart or Sap Rot
Heart or sap rot is a fungal disease that causes the wood in the centre of the trunk or limbs of the eucalyptus to decay. The length of time it takes this disease to decay the wood varies from a few months to several years. Heart or sap rot causes the wood to loose its strength, killing the sapwood storage and conductive tissues in the tree. No visible damage is usually seen unless the bark has been cut or damaged to reveal the cavity inside. To prevent this from happening, cut out any dead or diseased limbs. When you prune, make cuts so the rain will drain off that section, not collect there.