Macadamias battling mistletoe menace

Mistletoe making matters miserable for macadamias

Horticulture
HUNTING: Local consultant Chris Fuller, Hort Innovation relationship manager, Dumisani Mhlanga, research lead Professor Dave Watson, and research assistant Melinda Cook, on the lookout for mistletoe within macadamia orchards.

HUNTING: Local consultant Chris Fuller, Hort Innovation relationship manager, Dumisani Mhlanga, research lead Professor Dave Watson, and research assistant Melinda Cook, on the lookout for mistletoe within macadamia orchards.

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Mistletoe is hindering Qld macadamia production.

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MISTLETOE generally conjures up images of Christmas romance.

Not so for the macadamia industry.

The pest plant which overtakes a host tree has become a burden to growers as it spreads throughout orchards, particularly in the largest growing area, the Bundaberg region. 

A research investigation, led by mistletoe expert Professor Dave Watson from Charles Sturt University, is looking into the significant effect native mistletoes are having on production.

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Professor Watson said mistletoe was a parasitic plant that lived off the nutrients and water from a host tree.

"It uses the host tree as a root system to support its growth," he said.

"Mistletoe rely on birds to spread their seeds, in particular the Australian mistletoe bird that stems from the flowerpecker family and eats little else.

"The birds feed off the fruit but cannot digest the seed, and as such deposit them on to the branch of another tree, usually within minutes - causing rapid germination and sending a root into the host."

INSIGHT: Mistletoe expert Professor Dave Watson from Charles Sturt University, is investigating the significant effect native mistletoes are having on macadamia production.

INSIGHT: Mistletoe expert Professor Dave Watson from Charles Sturt University, is investigating the significant effect native mistletoes are having on macadamia production.

He presented his findings at a national grower meeting held in Bundaberg in December last year, where he suggested various control and management techniques for mistletoe, which are spread by birds that prefer mistletoe fruit.

"Unfortunately, the mistletoe is well adapted to infecting many of the popular commercial varieties which have more open, well-lit canopies which mistletoes love," Professor Watson said.

"Tree management that trims the crown and removes inner branches also encourages mistletoes to establish."

Professor Watson said he had already identified three individual species of mistletoe affecting macadamia tree crops.

"However, we actually have more than 90 different native species of mistletoe, 72 of which are endemic to Australia," he said.

"Mistletoe grows quite freely and unproblematically in the bush. The issue it raises with tree crops is that it diverts nutrients away from the host plant, and macadamia trees in particular, lose their ability to produce crop.

"A severe mistletoe infection can deplete a mature macadamia tree of all its nutrients within just three years, which if left unchecked, can cause the premature death of the tree."

Professor Watson said this research would help develop options to mitigate the deleterious effect of mistletoe on macadamia tree crops.

"Macadamias are the only horticultural crop in Australia to experience issues with mistletoe, and initial grower consultations have revealed that some of the newer varieties may be more susceptible to being affected," he said.

SPREAD: Mistletoe relies on birds to spread its seeds, in particular the Australian mistletoe bird that stems from the flowerpecker family and eats little else.

SPREAD: Mistletoe relies on birds to spread its seeds, in particular the Australian mistletoe bird that stems from the flowerpecker family and eats little else.

"This research will help to identify the underlying causes of increased mistletoe numbers in macadamia trees, and evaluate potential management options.

"Providing habitat for a native mistletoe feeding caterpillar and for wildlife who are partial to the taste of mistletoe could provide a low cost, and natural solution."

The project is being funded by Hort Innovation through the macadamia research and development levy and government contributions.

Control options

PROFESSOR Watson said he believes the most effective way to control mistletoe is to apply principles from integrated pest management.

"Monitoring orchards regularly for infection, regularly removing mistletoe branches twice a year, and adjacent growers work together to stop outbreaks can all help manage mistletoes in orchard areas," he said. 

"It has to be a joint effort by all who work in an orchard."

HINDRANCE: Mistletoe, with its yellow flowers, growing within a macadamia tree in a Bundaberg orchard.

HINDRANCE: Mistletoe, with its yellow flowers, growing within a macadamia tree in a Bundaberg orchard.

Professor Watson has also recommended that more research could also help fine-tune management practices.

"We need to know more about infection rates in different macadamia varieties in all growing regions and growing conditions," he said. 

"The use of thermal imaging via drones could help detect the extent of mistletoes across a macadamia orchard.

"Chemical control of mistletoes has been trialed in many forestry and plantation settings, but with mixed results.

"In addition, bird control such as lasers could deter mistletoes dispersers from orchard of used across the growing area, but this needs to be tested.

"Finally, we need to find out if mistletoes are also harbouring beneficial insects that may control mistletoes, suppress other insect pests or increase macadamia pollination.

DEMAND: Grown for its high value, moreish nuts, commercial macadamia orchards stretch from Mid-North Coast NSW to Central Queensland.

DEMAND: Grown for its high value, moreish nuts, commercial macadamia orchards stretch from Mid-North Coast NSW to Central Queensland.

"This may affect our management decisions."

Professor Watson said he was excited to be involved in this type of research in regional Australia.

"This is an example of where native ecology meets commercial agriculture, and both bring issues that need to be addressed as part of a complex interaction that includes man and nature," he said.

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