A New Approach to Avocado Tree Management

November 2014

A new approach provides more effective avocado orchard management

Whangarei’s Lynwood Avocado Nursery produces world-class micro-cloned avocado trees that are complete grafted plants, grown using a multiple cloning technique.

There are two nurseries in New Zealand producing clonal rootstock avocados. Lynwood produces a micro-cloned tree, which is 300mm long and 50mm wide, in comparison to a standard avocado ready for planting which is grown in potting mix in a large planter bag. Stephen Wade from Lynwood Avocados describes micro-cloning as the “Everest of plant propagation”. These micro-clones are grown in vermiculite or seed raising mix, and those in vermiculite can be easily exported, as they don’t have phytosanitary issues.

Fifteen years ago NZ needed clonal rootstock avocados. There was and still is, a lot of tree decline caused by the root-rotting fungus phytopthora. An essential tool in managing the phytopthora problem, along with good horticultural management practices, is to use clonal rootstocks selected for tolerance to phytopthora.

From the late 1990’s Stephen started experimenting with about 200 micro-clones a year, ending up with about six saleable plants the first time. The learning curve is very slow, and adapting the techniques to the NZ climate took a lot of work in terms of learning about timing and temperature. The South African avocado expert who developed the technique was very generous with his help.

Each year a few things went wrong, so Stephen changed the techniques a little and the second year he had 12 plants out of 200 that were saleable. It took a decade of practising before he commercialised the process at Lynwood, and another four years before they started producing volumes of clonal trees.

Stephen says they continue to run multiple trials all the time and each year at every step they get a little better. “We might get a 1% gain in one process each year and overall that adds up at the end of the year to maybe 5% gain, more efficiency and a greater success rate.”

The nursery rides the wave of confidence in the avocado industry. This season Lynwood is growing 25,000 trees, of which 20,000 are grafted seedlings, the other 5000 are clonal trees.

The main market is still New Zealand growers. The clonal trees are selected for phytopthora tolerance and they can survive in a lower oxygen environment. New Zealand is an unpredictably wet place on occasions and it only takes one weather event to drown the trees, which then go into a slow decline.

The clones used in New Zealand mainly come from South Africa where cuttings were taken from trees thriving in wet areas where surrounding trees had died from phytopthora.

The nursery has a manager and two other staff, while a fourth person works in the orchard, and Stephen counts himself as the fifth. “It’s a very good team, and most have been with me for seven or eight years.” They have exported trees to Japan, Korea and the Cook Islands and are just looking at a development in India and one in China.

There’s a planting boom going on again now, which is good news for nurseries. But to work out how many trees to grow, Stephen has to keep his ear to the ground and talk to as many people as he can in the industry. That’s because it takes two years from starting a plant to be able to sell it to a grower. “We are taking orders for 2015 and 2016 at the moment and we are sold out for this year.”

Another encouraging sign is that the government has just put $4.5m into a Primary Growth Partnership for industry research over the next five years.

The 10ha orchard was large when it was planted in 1983, but today is considered a medium sized orchard. Now Stephen is going through the old plantings and progressively replanting block by block. “We have some fantastic 30 year old trees, but where water has pooled they have drowned. A lot of these trees have been producing well for 15-20 years, but in one three day period we had 200mm of rain. The land just can’t drain the water quickly enough and with only one event the tree can start going downhill.”

Stephen is one of four growers who have replanted in a high-density manner. Older plantings were at 10mx5m, 7mx7m or 8mx8m. These plantings took a long time, perhaps a decade, to maximize production. “When you do the cashflow, the interest you paid waiting for the orchard to get to full production made it very expensive.” The high-density plantings are at 5mx3m and 6mx3m, so a full canopy is grown by year five. He started planting high densities two years ago.  Other orchards have been successful, but it does take careful management to get high-density plantings just right.

It’s a high capital cost at establishment, but a low operating cost once the trees are established, which reduces the cost of production per tray. “If we don’t adopt this latest technology we will get left behind. When the world price is $10/tray, if you don’t change and if your overheads are high, then orchardists will pull their trees out. We have to keep up.”

With a small tree, picking costs are a lot lower as you don’t need a hydralada. The trees can be sheltered properly, because the fruit on tall trees is often damaged by the wind. Taller trees which might be 10-12m in height often have smaller sized fruit, the result of the tree having to use more energy to get water to the top of the tree and move photosynthates to the fruit. High-density trees are not taller than 3m, so all the picking can be done from the ground, and hydraladas aren’t needed.

Unlike the apple industry where dwarfing rootstocks are used extensively in high-density plantings, the avocado industry doesn’t have any dwarfing rootstock. “The whole world is looking for a dwarfing rootstock.” Meanwhile Stephen is also growing several selections of avocado and working with an orchard consultant on this project.

“The best rootstock for NZ is probably already in NZ; we just have to find it.”