Because apples and pears were introduced to New Zealand both as graftwood and as trees, many pests and diseases were introduced at the same time. The most serious bacterial disease, fire blight (Erwinia amylovera), was introduced in graftwood from the US after the First World War. This resulted in a ban on the export of New Zealand pipfruit to Australia, which has remained free of the disease. The ban was lifted in 2011.
The other major diseases are black spot (apple scab, Venturia inaequalis) and powdery mildew (Podosphaera leucotricha). The former is more prevalent in wetter areas and the latter in drier regions. Black spot can cause major losses of fruit and leaves if not controlled with fungicide sprays. A major objective for New Zealand breeding programmes is to raise new cultivars resistant to these diseases.
Major pests of pipfruit include leafroller caterpillar (Tortricidae moth family), codling moth (Cydia pomonella), woolly apple aphid (Eriosoma lanigerum), leaf curling midge (Dasyneura mali) and red spider mite (Panonychus ulmi). Although these pests can be controlled by insecticidal sprays, much scientific work has gone into understanding their specific biology, and the role of predators and parasites in their control. Spray programmes in the 1980s relied heavily on broad-spectrum insecticides that were toxic to a wide range of insects, pest and predator alike. Pests became resistant to some of these materials, which has led to a greater interest in biological control.
Reducing chemical residues
By the early 1990s, consumers were concerned about the regular use of broad-spectrum sprays. The New Zealand pipfruit industry developed the Integrated Fruit Production (IFP) programme, which relies on ecologically safer methods. Trees are sprayed only in response to pests or diseases, rather than by the calendar. Chemicals are used which are primarily toxic to the specific pest, so predators and parasites remain unharmed.
The leaf-sucking European red spider mite became a serious pest in New Zealand apple orchards when it developed resistance to some spray chemicals. Other mites that ate the pest were also killed by the sprays. Growers now monitor populations of the red spider mite and its predators before deciding whether to spray. They often rely totally on the predatory mites to limit pest numbers and damage.
The IFP programme was introduced over a five-year period in the mid-1990s, and was readily adopted by growers. It is continually being updated as further work is done on pest and disease biology. In 2007 the pipfruit industry began trialling a zero chemical residue programme.
Organic pipfruit growers do not use synthetically-produced pesticides and fertilisers, but rely on older fungicides based on copper or sulfur, and organic fertilisers.
Most organic pipfruit production is in Hawke’s Bay, as the drier climate makes diseases such as apple scab and summer fruit rots easier to control. The rich soils also help with tree nutrition. The costs of production are higher, as it is more labour-intensive – but organic fruit sells for a higher price. Some growers have adopted organic methods for philosophical reasons, but for others it is a purely economic decision. In 2007 organic apples made up about 10% of the export crop.