Horticulture staff from the Department of Agriculture, Fisheries and Forestry (DAFF) can assist growers with advice on the management of cyclone-affected crops, such as how to manage and restore damaged trees, remedial measures to minimise future loss, and fruit management.
Fruit on the tree may have been affected by wind damage. Fruit may be bruised, and some may have cuts and chunks out of it. A copper spray at this stage will help to protect the fruit from both bacterial and fungal breakdown that will be aggravated by this damage. It will also protect damaged leaves and branches. Choose a product that leaves minimal residue such as red copper. Where growers have not been able to apply a protectant copper spray against anthracnose after the cyclone, an azoxystrobin fungicide can be applied (within the label´s resistance management guidelines) as it has some reach back ability.
Bruising and fruit damage will be clearly visible after a few days, and pickers should avoid harvesting damaged fruit. Treat fruit with normal post-harvest treatments, making sure that equipment is cleaned carefully if any fruit with bacterial soft rot goes through the packing line.
Some trees that have blown over can be salvaged if root damage is not too extensive, and pruning and propping may help the trees recover. Be careful when propping to avoid damaging the remaining roots. Stop lifting the tree if you hear cracking due to the root snapping on the down wind side. If in doubt, leave the tree as it fell and prune to a new shape over several years. Prune off a significant proportion of the canopy and treat limbs for sunburn (e.g. white acrylic paint). Treat the ground with a fungicide (against phytophthora).
Consider sunburn protection for fruit remaining on trees, as fruit is now more exposed since leaves have been stripped from the tree. This is particularly the case with Hass. A spray-on crop protectant is suggested. The volume used per tree will have to be gauged, and depends on canopy size and state. Sufficient volume needs to be applied to get good coverage, but not to the point of run-off.
Longer-term phytophthora control treatment
Normally a phosphorous acid injection is recommended for March, and this injection is more important than ever following heavy rain during a cyclone. Injections are favoured over foliar sprays because the leaf area needed to absorb the phos acid has been reduced by the cyclone, to the point where there is not enough leaf area to absorb sufficient phosphorous acid.
Macadamias are particularly brittle. Growers need to consider strategies for clearing tree rows, salvaging trees and the possible recovery of fallen nuts from areas where machinery access can be achieved.
Trees need to be pruned to take out any damaged and broken limbs. Also, apply white acrylic paint or a spray-on sunburn protectant to protect exposed limbs against sunburn. Pruning trees to a central main leader can provide more resilience to future high wind events.
Many trees break at ground level, and they will need to be replanted. Where trees have not broken, they can be propped and pruned to reduce the canopy and to assist the trees to recover. Open out the centre of the tree by removing selected internal branches.
The first step to recovery is to stand trees back up as soon as possible. When this is done and debris is cleared, spray all trees with mancozeb or copper. These fungicides are largely preventative in their action.