Spraying Techniques for Orchards

No matter what type of fruit is grown, an orchard attracts a host of pests and diseases trying to eat into your profits. Here are some of the more common ones and some techniques to keep them at bay.

The set-ups employed in orchards for pesticide spraying are usually air blast sprayers (use a normal cone nozzle) and air shear sprayers and rotary atomiser sprayers (designed for controlled droplet application).

Worms and caterpillars love apples and eat into both fruit and the leaves. Treatment involves applying a general insecticide once when buds first appear and then again roughly two weeks later.

Peach borers lay their eggs beneath the bark of stone fruit trees. Their larvae can cause major damage from boring, so you need to get to them before they hatch. A permethrin or carbaryl-based pesticide should be applied when the adults first lay their eggs, followed by another dose a month or so later.

Scale is another common pest that needs to be eradicated at the larval stage. Treatment of scale is to suffocate the colonies of eggs beneath the bark by spraying a horticultural oil called Dormant Oil. Higher spray volumes than those delivered by a common air blast sprayer are needed, so specialised equipment such as an oscillating boom sprayer or hydra sprayer is required.

Mites can be controlled using the same method, when followed up with an application of general spray mixed with miticide later in the season.

Fruit fly is another potentially damaging pest in orchards. Thorough coverage of trees with a conventional insecticide can kill eggs and young larvae in the fruit. As it has the potential to kill beneficial insects as well, this should only be a last resort after other control measures such as bait spraying and male and female traps have failed.

Weevils attack the leaves and bark of fruit trees and their larvae attack the roots. There are registered pesticides available for the control of weevils, although another method which slows their progress is to tie a dacron band around the trunk of each tree.

Sooty mould is a disease that affects the quality of citrus fruit and reduces photosynthesis in the leaves. Treatment involves spraying insecticide to eradicate insects such as aphids and scales, which secrete the honeydew that sooty mould grows on.

Weed control is also necessary in any orchard, and herbicide delivered by a boom sprayer is the most efficient method. This reduces the need for cultivation methods, which can increase soil erosion and damage tree roots.

There are many other pests and diseases which threaten fruit trees, including apple brown rot, apple maggot fly, apple scab, cherry aphid, cherry leaf spot, codling moth, European wasps, plum pox virus and silver leaf disease. All require different methods of control.

Whichever spray method is used, correct calibration of equipment is vital if effective pest control is to be achieved.

You should check your equipment regularly for wear (filter, nozzle, ball valve etc) and replace worn parts as required. Nozzle wear is the most common and is dependent on the material it is made from, the type of spray solution and the sprayer’s operating pressure.

Regular servicing is also necessary to keep your gear in top working condition, particularly hoses and pumps. Australia has spray equipment suppliers and service agents in each state and territory.

The primary concern when spraying pesticides in an orchard is to avoid over-spray, as chemicals dripping onto the ground will be absorbed by the tree roots and ultimately the fruit itself. You also need to consider the negative effects of strong pesticides on natural enemies of insect pests such as parasitic wasps, ladybirds and lacewings.

The issues associated with spraying chemicals have led to a growing interest in a more balanced form of pest management. This advocates the use of a range of different control methods, including introducing natural pradators, using more biologically-friendly sprays and taking more preventative measures to stop pests and diseases from gaining a foothold.

Pesticide spraying is still a necessary part of orchard pest management, but increased regulations now require that it be used more discriminately and accurately than ever before.

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