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Knapsack spraying techniques

Learn why different spraying techniques are needed for different types of crops and that how you spray depends on the shape of your crop, its culture and growing conditions.

Basics

It is important to spray your pesticide of choice in the right dose at the right time; to the right place; and that the pesticide remains where it is supposed to, in the best spread of spray drops.

You will need to make choices about:

  • spray mix/water volume
  • height or distance of your nozzle from the target surface
  • type and size of nozzle and drop size
  • spraying pressure
  • spraying speed.

And will need to calibrate your knapsack sprayer based on those choices. 

Technique is to do with the act of spraying: how you use your spraying equipment; how you angle and move your nozzle to direct the spray drops to your target surface. The best knapsack spraying technique for your crop will vary with:

  • the type of pesticide that you will be spraying
  • the shape of the crop (height, type, number and density of leaves)
  • its growing system (rows, beds, single plants, fields).

Types of pesticide

The type of pest to be controlled, how the pesticide works, and the size, number and site of the target pest will all affect your choice of spraying technique. 

Herbicides may be sprayed downwards:

  • onto soil or unwanted plants
  • as a pre-plant treatment before the crop is sown
  • as a selective spray after the crop emerges
  • as a directed spray between rows
  • as a spot spray to control single weeds.

Insecticides and fungicides, when sprayed on leaves, can be directed downwards, laterally or upwards. 

Pesticide type can also affect other choices on how best to spray, for example:

contact pesticides often need higher spray mix/water volumes and smaller drop sizes
systemic pesticides can allow you to spray larger, wider spaced drops over target surfaces.

Shape of the crop

The crop's height and type, number and density of leaves all affect your choice of knapsack spraying method: what spray mix/water volume to use; which drop size and the angles at which to direct the spray into and over the plant. 

Seek expert advice. Some sprays may be better pointed up and under one type of tree (e.g. citrus) whilst you may be able to spray others (e.g. apple trees) by moving the nozzle both upwards and downwards. The techniques used the most often are:

  • downward spraying techniques for lower growing crops
  • lateral spraying techniques for vertical walls of crops
  • upward spraying techniques for taller crops.

Growing system

Your crops could be growing in various ways:

  • in beds (e.g. many lettuce crops)
  • in low rows (e.g. cabbage)
  • in taller rows (e.g. tomato vines and coffee bushes)
  • in orchards (e.g. apple trees)
  • broadcast sown (e.g. wheat).

The growing system of the crops you are going to spray will also affect your choice of spraying technique: the spraying direction; the number of nozzles you use; and whether you should use a mini-boom or extension lance or a cluster of nozzles. 

When choosing your spraying method and the personal protective equipment (PPE) to wear, follow the advice on your pesticide label with care!