Windbreaks in New Zealand - 2001
Most of the New Zealand avocados are grown in a coastal environment not unlike that of the Santa Barbara/Ventura area. Being coastal, growers have learned from past experience that wind protection is necessary to maintain fruit quality and tree performance for a range of tree crops. Growers have elevated windbreaks to a high management level, and some of these techniques and windbreak plant material should be evaluated in the California environment.
Two major differences that need to be kept in mind are that this area gets substantially more rainfall than we get – up to 50 inches, generally well spaced over the year – and that the orchards in general are planted on flat ground, which allows for mechanical operations, such as harvest and pruning. This means that little irrigation is practiced, although some areas might benefit from irrigation in dry summers. They also can easily hedge the windbreaks to keep them narrow so as not to take up too much space.
The two major different types of windbreaks are artificial ones and growing ones. Artificial ones are built on 30-foot poles spaced at 20-foot spacings. Then, horticultural cloth, horticultural saran (like used for shade houses), or a polyethylene material as used to surround construction sites is spread between the poles. The height of the windscreen material depends on the height needed to protect the trees or vines. Although expensive, this system has the advantage of providing immediate protection, not requiring the years of preparation as is needed with a living hedge. It also can be taken down after the trees get to a size that they can protect themselves. They also don’t require water, root pruning to avoid competition with the crop and take up little space. On a smaller scale, growers will erect individual cages out of this material around trees. During wintertime they will cover the tops of the cages with shelter cloth to reduce frost damage.
Instead of the monotonous windbreaks of blue gum eucalyptus and ‘Lombardy’ poplar as seen in California, Kiwis employ a range of different living windbreaks. They use both deciduous and evergreen varieties. Deciduous breaks are used in the colder areas where winter frost protection is important. Popular deciduous varieties include Salix matsudana (an upright willow species), Dutch alder (which provides nitrogen as a side benefit) and a range of poplar species, such as Populus deltoids X ciliata, P. maximowiczii X niger and P. yunnanensis X szechuanuica. Root invasion into the orchard can be a problem with these species and root pruning is done on a regular basis, if the hedge is planted too near the first row of avocados.
Evergreen species are also used, such as Casuarina cunninghamiana (she oak), Cupressus lusitanica (‘Mexican’ cypress), and Cryptomeria japonica. The later species is much less of a problem when it comes to root competition with the tree crop. Clumping, giant bamboo is also used effectively, but root competition is also a problem with this species if planted too close to the first row of avocados.
With the advent of such pests as the lerps psyllid on eucalyptus and poplar rust on poplar in coastal environments, it is worth looking at other types of windbreak plant species. The ones used in New Zealand are all potentially new candidates and it would be worth trying them on a small scale.