Pesticide Application

The objective of all pesticide applications is to apply the correct rate of the recommended product uniformly to the target without contaminating non-target areas. To achieve this, suitable application equipment must be operated correctly and external environmental factors such as the weather must always be considered.

Calibration

Calibration is a procedure that will assure that the pesticide will be uniformly applied to the target at the correct rate.

A nonuniform application can occur from either a variation in nozzle output across the width of the boom or by localized variations occurring over the treatment area. Most common problems resulting in nonuniformity across the width of the boom are from variations in the nozzle orifice size, pressure or nozzle spacing. Most common problems resulting in localized variations in the treatment area are from variations in the forward speed, operating pressure, or boom movement. To ensure that a uniform application will occur each of the potential variations must be minimized.

Nozzle calibration is a procedure that assesses uniformity by determining the output of each nozzle on the boom. A visual inspection of the nozzle spray pattern should be made to detect nozzle clogging and/or damage. The output of each nozzle is compared to the average value of the set. In addition, the output value is compared to that of a new nozzle to assess the amount of wear. If a nozzle is worn by more than 15 percent it should be replaced. The spray pattern of worn nozzles becomes distorted and will disrupt uniformity. This distortion cannot be detected by a visual inspection.

Application rates can be determined by a mathematical formula. This allows the producer to quickly examine a variety of situations saving valuable field time.

For more information refer to the operator's manual or to Agriculture Canada's publication 1849 entitled Field Sprayers.

To determine the nozzle output for a particular situation, the application rate, average field speed and nozzle spacing must be known. Since the nozzle output is determined by both orifice size and pressure, a variety of nozzles at different operating pressures are capable of delivering the same nozzle output. The producer could select a small nozzle at a high pressure or a large nozzle at a low pressure, to deliver the same output.

High versus low pressure

In the past it was common to apply pesticides using nozzles with small orifices and high operating pressures. This created a very fine spray which gave good penetration and coverage when applying insecticides and fungicides. While these practices provided good control of the pests, they were not sensitive to environmental concerns about off-target drift. In applying pesticides today, the producer must consider the pest, crop, weather, environment, neighbours, government regulations and the consumer.

Today, potato producers still classify how they spray their potatoes as either high or low pressure. Since high and low are relative terms, this classification is primarily based on how the sprayer is operated. High pressure spraying refers to the selection of a small nozzle combined with high pressures which produce a spray consisting mostly of small droplets. Low pressure spraying refers to the selection of a larger nozzle combined with lower pressures which produce a spray consisting mostly of large droplets. It is important that producers realize that the main difference between high and low pressure spraying is primarily in the combination of nozzle and pressure used rather than specific differences between the sprayers.

Droplet size and spray quality

The selection of the nozzle size and operating pressure will determine the type of spray produced. Either increasing operating pressure or decreasing nozzle size will decrease the average droplet size produced. The spray quality produced by sprayer nozzles has been classified into VERY COURSE, COURSE, MEDIUM, FINE and VERY FINE (they are always written in capital letters to distinguish them from the general use of the words). In selecting the spray quality for an application the producer must consider the drift potential, penetration required, and the amount of coverage required.

Drift potential

The spray quality is directly linked to the drift potential of the spray. Small droplets can remain suspended in the air for longer periods of time due to their lower mass and slower velocity. It is during this time that wind can move the droplet horizontally across the field causing off-target drift. The finer the spray quality, the greater the spray drift potential. Producers can easily select a larger nozzle and lower pressure to change spray quality and reduce spray drift.

Spraying only when weather conditions are acceptable can also reduce drift. Excessive wind, high temperatures, low relative humidity and temperature inversions can all increase the drift potential. Spray when the following conditions exist: 1) wind is the lowest, 2) humidity is the highest, and 3) thermal air currents are moving downward toward the ground; that is, during dawn or early morning. Early afternoon is usually the poorest time to spray since the wind is generally the strongest, the humidity lowest and the thermal air currents move upwards due to the sun's rays heating the earth.

Keeping the boom close to the target reduces the distance the droplets have to travel and can reduce drift. For herbicide applications, the use flat fan nozzles with wider spray angles (110E instead of 80E) will allow the boom to be positioned at a lower height without altering the uniformity.

Flat Fan Nozzles

Flat fan nozzles are generally recommended for the application of herbicides. When properly installed and operated they can apply the pesticide uniformly to the target. Proper installation requires that they be overlapped and slightly offset from the adjacent nozzle. Flat fan nozzles are designed to work only at low pressures, namely 100 to 400 kPa. Operating outside the pressure range recommended by the manufacturer will distort the spray pattern and adversely affect uniformity. Even flat fan nozzles are recommended for band applications.

Hollow Cone Nozzles

Hollow cone nozzles are generally recommended for the application of insecticides/fungicides because they can be operated at higher pressures (400 to 2000 kPa) producing a finer spray quality. The uniformity of application is not as good as with flat fan nozzles yet, because the target (developing potato canopy) is a nonuniform surface, this criteria may not be limiting.

Raindrop Nozzles

The RD Raindrop nozzle is a type of hollow cone nozzle. It uses a standard disc/core nozzle in combination with a specially designed cap. The spray exiting the standard nozzle enters the Raindrop cap and is decelerated in a secondary swirl chamber. Upon exiting from the Raindrop cap the spray velocity is lower resulting in the formation of large drops. Producers using the RD Raindrop nozzle in combination with low pressures should verify that adequate penetration and coverage is obtained.

Rotary atomizers have been used in the application of pesticides to the potato crop. These nozzles use a metering orifice to control the flow rate and centrifugal force to create the droplet size. They produce a narrower range of droplet sizes which can enhance the performance of the pesticide. By simply varying the rotational speed of the nozzle the droplet spectrum can be changed without changing the output rate. It is common practice to reduce the amount of water being applied when using this technology. The efficiency of these units may not be better than that of properly operated standard hydraulic sprayers. Rotary atomizers are more complex and have higher initial and long term maintenance costs.

Many other specialty nozzles are available to provide a uniform application for different types of equipment and specific conditions. Nozzle catalogs are published by the nozzle manufacturers and are available from suppliers on a no charge basis.

Precautions before application

1. Properly identify the pest and determine what control measures can be taken.
2. If a pesticide application is required, select the pesticide that will provide the best control with minimal environmental effect. Read and follow instructions on the pesticide label.
3. Use application equipment that can apply the pesticide uniformly and minimize off-target drift. For field sprayers the correct nozzle will have to be chosen to apply the recommended rate depending on the field speed and nozzle spacing used. Calibrate the equipment on a regular basis.
4. Always evaluate the weather conditions immediately prior to any application to make sure that the pesticide reaches the target and has sufficient time to adhere to the surface.
5. Warn children and others of the dangers of pesticides and Be Prepared for Emergencies. Instruct them to stay away from the pesticides, sprayer and even the application site until it is safe.

Precautions during application

1. Obtain and wear all required safety equipment outlined on the pesticide label. During the mixing and loading operation the applicator is at the greatest risk since concentrated pesticides are being handled. Clean water tanks are recommended for all sprayers.
2. Triple rinse all pesticide containers immediately upon emptying them and add rinsate to the sprayer. Dispose of empty containers as recommended by the Provincial Pesticide Regulatory Agency or the Department of Environment.
3. Operate the equipment according to manufacturers recommendations. Maintain constant field speed and operating pressure. This will provide the greatest degree of uniformity. Select a forward speed that will prevent excessive boom movement. Set the boom height depending on the nozzle spacing and spray angle chosen to achieve a uniform application.
4. Be aware of changing weather conditions and their implications.
5. Follow the provincial regulations regarding the filling of sprayers, maintaining buffer zones, and any other requirements.

Precautions after application

1. Store surplus pesticides in a locked and marked storage. Specific provincial requirements may exist for buildings used to store pesticides. To dispose of unwanted pesticides contact the Provincial Pesticide Regulatory Agency or the Department of Environment.
2. Thoroughly clean the sprayer inside and outside. Wear the recommended protective equipment. The sprayer should be decontaminated when switching from herbicides to insecticides/fungicides as herbicide residues could result in crop damage. Follow pesticide manufacturer's recommendations for neutralizing agents and amounts.
3. Inspect the sprayer for any signs of wear or damage. Make any necessary adjustments and/or repairs.