Eucalyptus (Eucalyptus spp.) trees belong to the myrtle plant family and adapt well to a variety of climates. The evergreen plant group also contains large shrubs. The low-maintenance, fast-growing plants have low water requirements. A fungal infection causes browning foliage.
Eucalyptus trees are prone to the armillaria root rot or oak root fungal disease caused by Armillaria mellea. The fungus infects the tree from the roots and starts to rot the water- and nutrient-conducting plant tissues.
The disease is characterised by the gradual decline of tree health as it becomes water and nutrient deprived. Major roots and the lower trunk are the first to die. Foliage is stunted in growth and starts to yellow and brown accompanied with premature leaf drop. There is branch dieback starting from the top of the tree. Mushrooms often sprout from tree base. The entire tree eventually dies.
Armillaria root rot is potentially fatal. Use resistant varieties and keep trees in good health with adequate watering. Avoid planting in areas that had previously housed infected plants. Remove infected trees entirely with roots and air-dry soil before new plantings, as suggested by the University of California Extension.