Macadamia Tips

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  • Ian McConachie mentions that possible reasons why a tree does not fruit is that it is a seedling and slower to come into bearing, is over vegetative [too much nitrogen?] or the flowers have been lost to the Macadamia Flower Caterpillar or Botyris type fungi. Cross pollination [with some partner’s pollen] may result in earlier cropping, higher yields and higher kernel recovery. Some Hawaiian researchers recorded some cultivars as being self sterile but I have never seen a tree that does not fruit.
  • Autumn – Watch for the Flower Caterpillar. The adult is a small 6mm grey moth and it’s active in the first 4 hours after dusk. Monitor flowers fortnightly from May to July then weekly. A x10 lens is needed to find the eggs which are laid singly or in groups of 2 or 3 on buds or the flower stem. The entry hole becomes brown and often has a drop of sap exuding from it. When first laid they are white and later become yellow and are half the size of a pin-head. Commence when buds are 2mm long excluding the stalk and continue until full bloom is past. Spraying is required is 50-80% of racemes are infested. One spray when 75% of the main flowering has reached full bloom is advised.
  • Macadamias like cross pollination from a different tree. Apparently some cultivars are better at pollinating others.  Ref: Oscar – Hawaii
  • From a vet’s point of view it is very common for dogs to ingest the nuts and then because of the nut’s size and roundness, they cause an obstruction which can be very serious and could need intestinal surgery (risky and expensive). The other problem is that they are not radio-opaque so a diagnosis can be missed – bad news. For these reasons I would hesitate to plant nut trees in any public place where dogs may be exercised or in my own back yard if I had a dog who was likely to scavenge the nuts.   Ref: Val Coyle – Vet.
  • Dwarf Macadamia  A couple of nurseries are selling this plant. I spoke to the President of the Macadamia Society and he said there is no such registered variety and he had never heard of it. I rang Daleys and spoke with Greg and he said it was brought in by an South African years ago. Has a much smaller nut and is subject to twig girdling. Ref: Sheryl Backhouse
  • Dennis Ting relates his experience down in Melbourne on self-pollination and cross-pollination of macadamia trees. “On my previous property I planted one tree a hybrid “Nutty Glen”.  It produced small crops of nuts without any cross pollination and the nuts were full sized and had full sized kernels. On my current property I planted four hybrid trees “Nutty Glen”, “Beaumont”, “A4” and “A16”.  The trees flower at the same time and honey bees move from one tree to the next (in a hedge arrangement).  The “Nutty Glen” bears more nuts of the same size than the single tree did alone with the benefit of cross pollination and the other three trees also bear well too. As well as being different varieties I think it is important to have different genotypes e.g. “Nutty Glen” is by a Mr. Greber, “A4” and “A16” are bred by Bell and “Beaumont” is by a Dr. Beaumont. I have chosen hybrids as the more readily available Hawaiian Integrifolia do not grow well in this cold climate and Tetraphylla although suited to a cooler climate have spiny leaves and are more difficult to handle.”
  • Plant Pathologist with the Tropical Fruit Research Station at Alstonville, Gordon Stovold is looking into an outbreak on the Northern NSW coast of the Anthracnose Husk Rot disease. The disease has been associated with heavy shedding of maturing nuts after a period of hot and humid weather. Anthracnose is evident when maturing nuts appear blackened and often gains entry to the nut husk at points of insect damage. Black Spots appear on the green husk and then join together to form a greasy decay which penetrates to the shell. The nuts will then fall to the ground before reaching maturity and often develop bright orange spore spots on the blackened husk. The fallen nuts are also capable of further infecting trees. You can use copper oxychloride at label rates to control further spread of the disease in case of worsening hot conditions. A single spray late in January may not reduce the current infection rate but should limit further spread of the disease which will be influenced by weather conditions. Remove all fallen nuts and separate them from the main crop.
  • To stop the Macadamia flower eating caterpillar, mix up some pyrethrum and pest oil according to directions on the packs and spray it on once a week while the tree is in flower. Pyrethrum is a contact killer – it is not residual or systemic and the pest oil is to make it stick. One of my rare trees is an Artocarpus hirsuta – it has only fruited once and the fruit was a mixture of sweet & sour and looked like a tiny little jackfruit with ariels inside.
  • Macadamia Nut Poisoning of Dogs   by Sheryl    After attending a weekend of talks at Fairhill Nursery last year where I caught up with Nan & Hugh Nicholson (they wrote that excellent series of rainforest books) Nan mentioned that in certain species of Macadamia the kernels contained traces of cyanogenic glycosides.  This was the first I had heard about toxicity in Macadamias and thought I would go looking for other sources of information to do an article for our newsletter. Our previous Guest Speakers Merv & Elwyn Hegarty also knew about it and sent me some detail on the subject. The final piece of information came while I was attending a lecture by Dr. Ross McKenzie on “Cyanide, Strychnine Bush and other poisonous hazards in the Queensland flora”. He sent me an article that appeared in Australian Vet Practitioner 30(1) March 2000 and to summarize: Plants in the genus Macadamia (family Proteacae) are endemic to eastern Australia (seven species) and Sulawesi in Indonesia (one specie) (Gross 1995) Macadamia tetraphylla, M integrifolia and hybrids of these species – variously known as the Macadamia Nut tree, Qld. Nut tree or Bopple Nut tree are cultivated in Australia, Hawaii and elsewhere for the edible kernels. Some kernels of these species contain traces of cyanogenic glycosides while the kernels of M. ternifolia and M. whelanii contain significant amounts of cyanogenic glycosides, are bitter and not currently used as human food (Aboriginees would remove the toxins before eating them (Gross 1995). In the clinical study, thirteen adult dogs of both sexes, various ages and at least five different breeds  developed sudden onset of various combinations of either paralysis, pain in the hindquarters, listlessness, limping 6-24 hours after eating several kernels etc. with one Rottweiler being given 2 tablespoons of macadamia butter.  All dogs recovered within 24 hours. The close association between ingestion of kernels and the onset of the syndrome in dogs and the consistent signs displayed among cases strongly support the hypothesis that toxicity from a chemical or chemicals in the kernels was responsible for the syndrome. Such chemicals may well be part of the plant’s defence system protecting its genetic material from attack by insects or microbes. The only known toxins in Macadamia spp. are cyanogenic glycosides. In one case where roasted kernels were fed, it indicates that heat does not denature the toxin or toxins. Given the widespread consumption of Macadamia kernels by humans and the lack of reports of subsequent poisoning, this syndrome appears to be a further illustration of the differing reactions of mammalian species to plant toxins. Dogs and humans for example differ significantly in their likelihood of being poisoned by theobromine in chocolate (from Theobroma cacao) and their susceptibility to N-propyl disulphide and thiosulphates in onions (Allium cepa). Dog owners should be warned not to regard their animals as “small humans”. As M. ternifolia is native in the area where I live, I rang our local Veterinary Clinic which has a large country practice (the Vet is an ex-President of the Australian Veterinary Association) and they said they have never come across this syndrome in their practice. I am a little surprised by this as our “Chuck” (actually – Charles Henry Robert Backhouse – the Bull Terrier) who actually belonged to the neighbour but lived at our place during the day could crack an unshelled nut with his teeth – loved them!