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Growing quality manuka

PLANTATION manuka should be cultivated as a horticultural crop rather than developed from a forestry mindset, said WildCape Manuka Honey founder Bill Savage during a recent field trip to his plantation at Ahititi, Waimata Valley.

Mr Savage's 30 years' experience as a commercial beekeeper includes business training and a science-based approach to planning and implementation.

“We are about farming nectar,” he said during the field trip.

Manuka flowers require a combination of heat, light and moisture. Plants at each specific location should have evolved over time to fit the annual flowering to when those conditions are optimal. Selection of site-specific genetic material is key, he said.

Manuka flowers require a combination of heat, light and moisture that fits within the annual flowering window for a specific site. Selection of site-specific genetic material is key, he said.

At Ahititi, seeds are sourced from manuka plants that have shown, over successive seasons, to produce good quantities of nectar. These are tested in a laboratory and selected to ensure the plant's nectar contain high levels of dihydroxyacetone (DHA).

DHA is a precursor to methylglyoxal or MGO, the natural compound in manuka honey that gives it unique anti-microbial properties sought after by markets. Research from the 1980s, particularly by the late Dr Peter Molan and his colleagues at Waikato University, has shown manuka honey with MGO levels above 500mg/kg to be valuable in human health, particularly topical wound healing, said beekeeper Barry Foster who co-organised the field trip on behalf of the East Coast Farm Forestry Association.

“The aim in establishing plantations of manuka is to grow plants that consistently produce manuka honey tested to this level.”

As part of plant selection to breed from those that consistently produced high levels of DHA in their nectar, Mr Savage and his team collected nectar from manuka flowers at Ahititi over successive seasons. This involved the collection of flowers, extracting the nectar and having that nectar analysed in a laboratory. The end result was a selection of six to eight local genotypes per year from which seeds were obtained and grown at the Native Garden Nursery at Makaraka.

This selection process was repeated on an annual basis over the past six years. Six to eight genotypes were selected each year to create a diverse, high-producing gene pool, said Mr Foster.

To get the right combination of climate and soils, site selection is important, Mr Savage told visitors to Ahititi.

A coastal site subject to summer drought is likely to result in an early nectar production window when there is still some moisture around. A site at too high an altitude will not get sufficient heat to produce the required levels of nectar until mid-summer. If the manuka plants are not producing good nectar, bees are likely to be attracted to other plants such as clover rather than the manuka flowers.

Sites with a good history of manuka honey production are best, he said.

The block was planted out over successive winters. Spot spraying of 600mm spaces in long grass several months prior to planting was important to provide sufficient space for the young manuka plants to grow while at the same time not opening up too much space for weeds to take over, said Mr Savage.

Controlling feral browsing animals such as goats and deer is critical as they can rapidly browse out planted blocks before manuka plants are mature enough not to be adversely affected by them.

One major issue in managing manuka plantations is to manage the re-growth of other native plants. In the right conditions kanuka could quickly overtake manuka.

“The idea behind vertical row planting is to allow natural manuka re-growth between the rows and to eventually take out the planted rows with a scrub bar after, say, 10 years production,” said Mr Foster.

“By doing this, new kanuka is effectively suppressed before it can seed and add to the existing seed bank in the soil.”

PLANTING MANUKA: Manuka is planted in rows on hill slopes at three-metre by three-metre spacings at WildCape Manuka Honey founder Bill Savage's Waimata Valley plantation, Ahititi. This allows sufficient light to grow a plant that flowers well while genetic selection lifts the average levels of dihydroxyacetone (DHA) in nectar to produce a consistently higher value honey than previously produced at that site. Picture supplied