Pipfruit are deciduous tree crops that require a period of winter chill. During their dormant period, apple and pear trees are reasonably resistant to New Zealand’s cold temperatures, frost and snow, especially as winter temperatures are not extreme by world standards.
Once spring arrives and buds begin to open, the young leaves and flowers are sensitive to spring frosts. In the past, this caused major crop losses. Today, growers use water sprinkling (in Central Otago) or wind machines (Hawke’s Bay) to reduce the chance of frost damage.
Hail can also cause major production losses. Hail storms are generally quite localised, but within a few minutes can turn potentially high-earning crops into fruit only fit for processing into juice. Many growers have hail insurance against possible losses. The only means of protecting against hail are choosing an appropriate location, and placing hail netting over the trees. A few growers use hail cannons, which send shock-wave blasts into the air in an attempt to stop hail forming.
Drought can seriously reduce crops and fruit size, but most orchards in New Zealand are irrigated.
Apples and pears grow best on well-drained soils with good moisture retention. Orchards need high soil fertility, as each crop takes up a lot of nutrients.
Apple yields in New Zealand vary from 50 to 100 tonnes per hectare. A crop of 70 tonnes removes around 82 kilograms of potassium, 31 kilograms of nitrogen, 7 kilograms of phosphorus, and 4 kilograms each of calcium and magnesium from each hectare of soil. These nutrients have to be supplied either from soil minerals or by adding fertiliser.
Some of the fertile soils in Hawke’s Bay have enough nitrogen, so nitrogen fertilisers are not used. Nelson soils – especially on the Moutere gravels – are generally poorer, and each hectare needs 50 kilograms of nitrogen, 13 kilograms of phosphorus and 70 kilograms of potassium added annually.
Calcium and apples
Although the fruit crop depletes only 4 kilograms of calcium per hectare, calcium deficiency can be a problem for apple trees in New Zealand. Most trees are sprayed with dilute calcium salts from November to harvest time (around February to May) to prevent bitter pit – a disorder caused by low calcium concentrations in the fruit flesh.
In New Zealand soils, apples and pears can suffer from nutrient deficiencies, particularly of magnesium, manganese, boron and zinc. These are normally addressed by leaf sprays.