Macadamia trees on the Northern Rivers' floodplain were given an acid-test during recent floods with mid-Richmond valley trees bearing the brunt of record inundation.
Grower and consultant Robbie Commens, manager and partner of an 100,000 tree plantation at South Ballina and the driver behind substantial flood plain plantings in recent years, says there is every reason to expect less than a 10 per cent loss of inundated trees with almost nil long-term damage to those older than three years - even if they spent days under water.
Water covered trees by one to two metres for up to a week and a fortnight later dead leaves illustrate the level of stress but scratch the bark and the cambium layer is green. Trees older than eight years appear unaffected and harvest continues; those older than three years have brown skirts but are flushing new leaves from their tops while those under one year old remain touch and go.
"Young trees in the ground are most vulnerable and unfortunately in this catchment 20-30pc of plantations are less than one year old," he said.
Some "dead" trees were pruned back to encourage flushing but Mr Commens, working with DPI advisers, found swelling bud nodes on branch tips so have ceased that work.
"If we have a 20pc loss of trees then this floodplain industry will lose some of its positivity," admitted Mr Commens. "If we lose less than 10pc then we will be popping the champagne corks and if that figure is less than 5pc the floodgates of confidence will open."
Ethephon-inhibiting spray is currently being applied by drone to limit leaf-drop and will be followed by a pesticide to counter starving loopers and twig girdlers.
The farm is too soft to support a tractor, now covered with a 20mm thick top-dressing of flood mud.
Macadamia agronomist Janus Erasmus said application of humus, molasses and kelp products to the roots of affected trees would stimulate new growth but full impact of this flood and the potential for disease down the track won't be known for three to four months.
- Read more in this week's The Land newspaper.
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