Avocado orchards need taller shelter

Elaine Fisher

The shelter on many Bay of Plenty avocado orchards is not tall enough nor properly maintained to provide adequate protection from high winds, says Hugh Moore of Morris Moore Farms, Katikati who has been orcharding in the district since the 1970s.

In his opinion, that’s why ex-cyclone Dovi caused so much damage to avocado orchards when it hit the region on February 13 this year. “Driving around, you can see the tops of the avocado trees above the shelter which is not good. We have 60 foot (18.28m) high shelter around our blocks at Kauri Point and we got off lightly from the wind. We didn’t lose any trees and had little to no fruit on the ground in our sheltered blocks.”

Other orchards were not so fortunate with trees ripped out, limbs broken off and hundreds of fruit waiting to be picked, stripped from trees. On Morris Moore Farms blocks which were more exposed to the wind (which reached gusts of more than 100kph, and blew from the north), some fruit was lost but the big problem for Hugh and other affected growers, will be wind rub damage to fruit which stayed on the trees. “It’s tragic really because next season looked like it would be the New Zealand avocado industry’s year as Australia won’t have such a large crop, Asia is hungry for it and many of the shipping issues caused by Covid should be over. “However, the scars left by wind rub will continue to grow as the fruit grows and any damaged fruit will only be good for oil.”

To adequately protect avocado trees, Hugh says shelter should be taller than the trees and the ideal tree species is cryptomeria, not the often-favoured casuarina. “Cryptomeria doesn’t get wide at its apex and doesn’t need topping. Many shelter trees are planted too closely together. The spacing should be 2.5m to 3m, not 1.25 to 1.5m and the bottom branches of the cryptomeria should be removed to allow the wind to blow through and not create a suction effect when it hits a solid barrier.”

Taller shelter needed

“The scars left by wind rub will continue to grow as the fruit grows and any damaged fruit will only be good for oil”

Hugh says the science behind effective shelter, which protects trees and stops wind spiralling into orchard blocks, has been around for decades but is often not understood by newcomers to the industry, nor many consultants. “Too many avocado orchards have the same height shelter as kiwifruit blocks and kiwifruit structures are around two metres high. In orchards avocado trees grow to 30 feet (9.14m) so kiwifruit shelter is no good. Avocados are jungle trees and left unpruned can reach 12 metres (40ft) high. Internal shelter has also been removed from many avocado orchards, leaving trees exposed to wind damage.” Ex-cyclone Dovi brought high winds, Hugh says, equal to those of Cyclone Giselle, (also called the Wahine storm) of April 9, 1968, which caused wide-spread damage throughout the country. That day the inter-island ferry the Wahine ran aground in Wellington Harbour with the loss of 51 lives.

“Those storms were extreme, but we get very high winds every decade or so, often in May. One in October, just before harvest about 20 years ago hit Kauri Point badly. A neighbour who had removed 70 to 80 foot (24.3 m) shelter trees had avocado trees blown right out of the ground. “We picked up 36 bins of fruit off the ground and that was only about one third of what was there. Another neighbour who had poplar trees as shelter, the same height as his avocado trees, lost 32 bins of fruit.” The lesson to be learned from all those wind events is, says Hugh, that well-spaced, maintained and tall cryptomeria shelter can’t be beaten for effective protection.