Following a cyclone, the high amount of root damage and tree stress may result in fruit and nut trees being susceptible to soil pathogens such as Phytophthora and Pythium species, which are a normal component of the soil environment. There are registered products (e.g. phosphoric acid and Ridomil) for control of those disease pathogens in some crops (see the Australian Pesticides and Veterinary Medicines Authority).
Diseases in the tops of the tree may be best controlled by regular applications of copper fungicide over the 1-2 months following a cyclone.
Cover badly damaged limbs, or breaks that cannot be cut cleanly, with a mix of copper hydroxide, water, and acrylic paint (approximately 1:1:1 - thicken or dilute as required) to help prevent disease. A more dilute version of the mix without the fungicide will also be suitable for sunburn prevention.
Tree trunks and major limbs that have been suddenly exposed to full light will be prone to sunburn. To protect them spray them with a 1:4:20 mix of water-based white acrylic paint, micro fine lime and water (i.e. 1L paint, 4kg lime and 20L water).
Cloudy and wet weather is helpful to trees that need time to recover.
Water and fertiliser management
Trees that have suffered major foliage loss still require water. Irrigation regimes should be more frequent, although for shorter durations, to ensure that the root zone remains moist, but not waterlogged. Overwatering may cause root rot.
Fertiliser inputs to damaged trees are recommended in small doses. Generally, the fertiliser amount should be reduced in proportion to the leaf or canopy loss. As new leaves develop, use a foliar application or frequent small amount of your usual fertiliser application.