Application Methods

Plant protection products can be applied in various ways. The manner of application should be stated on the crop protection program.

Application methods include:

• Foliar spray application
• Trunk application
• Soil drench

There are many variations of application methods. The decision on which method to use depends on the specific requirements and purpose.

Foliar Spray Application

The most common method of applying insecticides and fungicides to plants (trees on an orchard farm) is by applying a foliar spray. This means that the spray material is applied to the leaves of the trees. There are three main types of foliar spray applications, being:

• Light cover spray
• Medium cover spray
• Full cover spray

Light Cover Spray

As the name suggests, these sprays are applied at low volume and with a light covering of the tree canopy. The droplet size is small; therefore, the spray is applied in a fine mist. The application of chemical bait is usually done by aerial spraying at a low volume.

The volume of spray material applied per tree during a light covering spray varies, depending on tree size and shape, but ranges from half a litre to three litres per tree.

Medium Cover Spray

Medium covering sprays are the most common form of application. It wets the foliage of the tree to the point of run-off. (Run-off means to the point where the water starts dripping from the leaves.)

The tree canopy is not necessarily penetrated, but some of the branches may be slightly wet.

The volume of spraying material applied per tree during a medium cover spray varies, depending on the size and shape of the tree, but ranges from 10 to 20 litres per tree.

Full Cover Spray

Full covering sprays are designed to thoroughly wet the tree canopy and penetrate the inside of the canopy, drenching the branches and framework of the tree as well.

The volume of spraying material applied per tree during a full cover spray varies, depending on the tree size and shape, but ranges from 20 to 50 litres per tree.

Trunk Application

Some chemicals can be applied directly to the trunk of the citrus tree. These chemicals are systemic, meaning that they are absorbed through the bark and being translocated within the tree to the area where they are required.

Soil Drench

This method implies the diluting of a chemical in water and pouring it onto the soil around the trunk of the tree where it is absorbed by the roots and translocated within the tree. These chemicals are also systemic. Certain chemicals can also be applied through a drip irrigation system which allows its uptake by the roots.

Application Equipment

Once the method of application has been determined, the equipment required for the application is identified and checked. Application equipment and measuring equipment is required during most applications. The crop protection manager determines the equipment requirements by taking into account:

• The area or number of trees to which the chemical must be applied.
• The time period in which the application must be completed.
• The number of farmworkers available.

Once the equipment requirements have been determined, the crop protection manager must consult with:

• The person responsible for mechanical equipment ensures that sufficient equipment (tractors and spraying machines) will be available.
• The person responsible for the stores to ensure that sufficient measuring equipment and chemicals are available.

The crop protection manager must also ensure that all equipment is in good working order, as breakdowns during application can cause delays that may result in ineffective pest and disease control. Spraying machines and tractors are normally serviced before the start of a season but must be checked regularly. The crop protection manager must consult with the person responsible for mechanical maintenance in this regard.

The application equipment that is required is specific to the application method.

Foliar Applications

Foliar applications can be applied in a number of ways, being:

• Knapsacks
• Handguns
• Mist blowers
• Crop sprayer aircraft

Knapsacks

Newly planted trees, up to the age of one year, maybe sprayed with a knapsack as they require very little spray volumes.

Be careful not to use a knapsack for the application of insecticides after it was used for the application of herbicides due to possible damage to trees.

Handguns

Trees between the age of two and four years old, depending on the cultivar planted and the area in which it is situated, are too big to be sprayed with knapsacks, therefore one will use handguns.

A handgun implies a spaying cart with a hosepipe and a spray gun held by an operator when applying an insecticide. With handguns, as opposed to knapsacks, a much higher volume of spraying material can be applied in less consuming times.

Mist Blowers

The most popular automatic spraying machines are called mist blowers. These machines work on the principle of air displacement. The air within the tree is “blown out” by the high-speed fan on the spraying machine and replaced with chemical-filled air. There are many different types of mist blowers. They can be broadly classified into low, medium and high-profile machines. The choice of machine depends on the type of spray required. For example, low- and medium profile machines would not be suitable to apply a full cover spray to large mature trees.

Low Profile Machines are double-sided mist blowers without any tower or deflector.

Medium Profile Machines are raised, double-sided machines with or without a single-sided deflector or a raised machine with a short tower.

High Profile Machines are single or double-sided mist blowers that have tall towers and cover the tree canopy from top to bottom.

Tractors are used to pull spraying machines. Power from the tractor is transferred to the spraying machine by means of a power take-off (PTO) enabling the pump, fan and spray tank agitator to operate. The PTO is a short sprocket at the back of the tractor which is connected to the spraying machine by means of a PTO shaft.

PTO Shaft

Crop Spraying Aircraft

Where large areas have to be covered in a short period of time, aerial applications (very expensive) is often used. Aerial applications can however only deliver light covering sprays and are therefore generally only used for bait sprays.

Trunk Applications

The number of chemicals, when applied in a trunk application form, must be measured very accurately. Specialised equipment, which is calibrated very accurately, is used for this purpose. The most common applicator is called a Calibra.

Some farmers use a paintbrush for trunk applications. The quantity of product required is calculated according to the diameter of the tree trunk. There are tables available that indicate how much chemical to apply to trees of different sizes.

Soil Drench

The chemical solution is applied to the soil by using measuring cups or jugs which ensure with relative accuracy that the correct quantity is applied.