Pesticide Application

Table of Contents

1. Treatment Time
2. Rate and Method of Application
3. Equipment
   • Sprayers
   • Dusters
   • Use and Maintenance of Equipment
   • Equipment Calibration
     • Hose-end Sprayers
     • Calibration for Ground Spraying
     • Calibration When Spraying Trees and Shrubs
     • Pressure Sprayers
   • Granular or Dust Applications
4. Related Links

Treatment Time

The time of application stated throughout this publication applies to the part of Ontario south of the line from Ottawa to Sudbury. Even in that area, the emergence of insects varies according to temperature and growth conditions. These differences are greatest in the spring and gradually disappear by midsummer. In addition, weather conditions vary from year to year and some judgement is needed regarding the timing of treatments. The same principle applies to the northern parts of Ontario where spring is late.

Treatment times and intervals are usually based on the life cycle of a pest, or on the residual activity of the pesticide.

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Rate and Method of Application

Always use the rate of pesticide specified on the label. Higher rates may cause injury to plants, kill beneficial insects and leave harmful residues on edible crops. Lower rates may result in unsatisfactory pest control.

The rate of application for spraying pesticides depends on the concentration of the active ingredient in the product. Different rates of the same product may be needed for the control of various insects or diseases. Spray mixtures using very hard water have a shorter period of effectiveness than sprays made with medium-hard or soft water. If your tap water is very hard, use rain water if possible.

Spray Applications

Rates for spray pesticides are expressed by volume of water. Read the label carefully before mixing any pesticide with water, to ensure that the correct rate is used. When applying the spray, the leaves, stem and fruit should be covered from all sides until they drip. Do not apply sprays when temperatures are 27°C or higher, as plant injury is more likely to occur. If it is necessary to spray during hot weather, do so in the morning or in the evening. Plant injury is also more likely when the air is very humid, causing slow drying of the spray.

Soil or Lawn Applications

The rates for soil or lawn applications are based on the surface area. The volume of water is not important as long as it is sufficient to cover the area. The rate of application depends primarily on the type of sprayer used because coarse sprays apply more liquid than fine sprays.

Dust Applications

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Equipment

Sprayers

The following types of sprayers are available:

• Portable tank sprayers with 4-15 L capacity suitable for medium and large gardens. They operate by pumping air into the tank before spraying is started or during the spraying operation. Keeping the air pressure as high as possible improves coverage and penetration within the plant canopy.
• Bottle-type sprayers with 0.5-1 L capacity for small gardens and for spraying a few plants. They operate by continuous squeezing of the handle during spraying. This type of sprayer is not suited where there is dense foliage or where the pest or disease is on the lower leaf surface.
• Hose-end sprayers operated by the water pressure in the garden hose. The highly concentrated spray mixture is siphoned from the jar into the water stream from the hose. Hose end sprayers do not work well if the water pressure is low or for wettable powders at rates of more than 100 mL per 5 L of water. A potential problem with this type of sprayer concerns the valve in the head. If this becomes defective, the concentration of the spray may be higher or lower than intended. Test the accuracy of the sprayer at least once a year by spraying a certain volume of water into a pail and comparing it with the measurement on the jar.

It is recommended that you do not use the same sprayer that was used for weed killers to apply insecticides and fungicides because it is very difficult to adequately clean weed killers from a sprayer. Doing so may cause severe injury to plants. If this is not possible and only one sprayer is available, clean the hose and tank very carefully to make sure that all traces of herbicide are removed. After rinsing, add 1 mL of household ammonia or baking soda per L of detergent solution, and let this mixture stand overnight in both the tank and hose. The next day, empty the sprayer by spraying the solution out through the nozzle, and rinse the tank with clean water.

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Dusters

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Use and Maintenance of Equipment

The purpose of dusters and sprayers is to distribute pesticide on affected plants or soil thoroughly and evenly. Poor pest control is often the result of improper or poor distribution.

The kind of pesticide application equipment you will need depends on the type and size of the garden. For a few low-growing vegetables and ornamentals, a simple duster or dusts in shaker packages are satisfactory. For fruit trees and large plantings, a compressed air or knapsack sprayer will be required. The rates applied with these sprayers can be closely controlled. Their range can be extended to cover tall trees by adding sections to the sprayer wand or by using ladders. Trees over 7.5 m usually require a high-pressure power spray for thorough coverage. Since power equipment is expensive, it is usually more economical to hire a commercial pest control firm.

Garden hose sprayer attachments are not recommended because the amounts they apply are variable and difficult to regulate. If there is no other alternative, see Equipment Calibration for details on calibrating a hose-end sprayer.

Do not use garden sprayers in the house. If pesticides are to be used indoors, apply them with a small hand sprayer, a paint brush, or an aerosol can.

If sprayers are properly maintained, they can give many years of service. Some pesticides are corrosive to metal parts, so it is important to rinse and wash out the tank with detergent or soap solution after each use. Leave the tank uncapped and upended during storage to allow it to dry without rusting.

Worn shut-off valves and leaky hoses or joints should be replaced immediately. Faulty sprayers increase the hazard to the applicator and give poor results.

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Equipment Calibration

As we have noted, pesticides are recommended at specified amounts per area or per volume (e.g., 10g/100 m2, 10 mL/100 m2, 5 mL/L). To know exactly how much pesticide is being applied, it is essential that your equipment be properly calibrated.

Hose-end Sprayers

Hose-end sprayers are not recommended for the application of pesticides because most do not give an accurate dosage and few can be used to apply wettable powders. If a hose-end sprayer is your only option, however, there are steps you can take to improve its effectiveness.

• Before connecting the hose-end sprayer be sure it is in good working order and the siphoning tube, nozzle and filter screens are clean.
• Open the tap fully while spraying with a hose end sprayer.
• Avoid running the water from other taps on the premises to help maintain a more constant water pressure.
• After use, flush both the sprayer and the garden hose with water.

If an instruction sheet on calibration was included with your hose end sprayer, use those instructions. Otherwise follow these steps:

Calibration for Ground Spraying

Do a test spray first, using water only, to determine the correct application speed, as follows:

1. Connect the garden hose to the water tap and hose end sprayer.
2. Adjust the sprayer nozzle to the desired setting (narrow stream, fan shaped, or mist).
3. Fill the sprayer bottle with water. Ink or food colour can be added to make it easier to see the amount of water in the bottle.
4. Mark off a 10 m x 10 m area using a measuring tape, pegs, and string.
5. Turn the tap on fully.
6. Walk back and forth over the marked off area, spraying until the area is covered. Remember the pace of walking and do it at the same rate thereafter.
7. Turn the water tap off and read the amount of liquid left in the sprayer bottle. The difference between this reading and the full mark is the amount of coloured water (pesticide) used.
8. If the pesticide container label indicated to use 10 mL/100 m2, and 10 mL were used, then this was the right amount. If more or less than 10 mL/100 m2 were used, adjust the application rate accordingly by walking faster or slower while spraying.
9. Empty the coloured water from the spray bottle and refill it with the required amount of pesticide and water to treat the infested area. Turn the water tap on fully and spray the infested area. Thoroughly rinse the sprayer and sprayer hose with water before storing it.

Calibration When Spraying Trees and Shrubs

Do a test spray first, using water only to determine the concentration of pesticide you will have to use, as follows:

1. Fill the sprayer bottle according to the manufacturer's instructions. Where the instructions state to use a pesticide concentrate, replace that amount with coloured water. Measure all liquids that go into the sprayer bottle and calculate the percentage of coloured water in the total volume of liquids in the sprayer bottle.
2. Connect the hose end sprayer to the garden hose, with the spray deflector removed (if possible). Spray into a pail marked at 1 L intervals and fill the pail to the 2 L mark. Turn off the water.
3. Measure the amount of coloured water (pesticide) left in the sprayer bottle and divide by 2 to determine the amount used per litre of spray in the pail. Multiply this amount by the percentage of coloured water in the bottle. This is how much coloured water (pesticide) was used in 1 L of spray. Compare this with the recommended dosage of pesticide on the label. If more pesticide was used than recommended, dilute the mixture in the sprayer bottle. If less pesticide was used than recommended, increase the concentration of pesticide in the sprayer bottle.

Pressure Sprayers

When filling the sprayer always use a funnel with a very fine screen to filter both the pesticide and the water. This prevents debris from getting into the sprayer and clogging the nozzle.

Do a test spray first, using water only, to determine the correct pressure and application speed as follows:

1. Mark off a 10 m x 10 m area with a measuring tape, pegs, and string.
2. Measure 4 L of water into the sprayer (1 Imperial gallon sprayer holds 4.5 L, 1 American gallon holds 3.8 L).
3. Pump air into the sprayer. The higher the air pressure inside the tank, the faster the spray will be discharged. Use high pressure to spray for insects and diseases, low pressure for weeds.
4. Adjust the nozzle to desired pattern. (For weeds, a nozzle with a flat spray pattern is used. For insects and diseases, use a nozzle that delivers a hollow cone spray pattern.)
5. Spray the measured area by walking over it and moving the wand slowly from side to side about 30 cm above ground level.
6. When the area is sprayed, release the pressure by slowly unscrewing the sprayer lid. Let's assume that all the water was used up. Now it is known that, if that pressure and walking pace are maintained, it takes 4 L to spray 100 m2.
7. If the label states to use 5 mL of pesticide/L of water, and to use 4 L of mixed spray/100 m2, then add 20 mL of pesticide to the 4 L of water and spray it on 100 m2.
8. If an upright plant, shrub, or tree is to be sprayed, spray it with enough water to wet the leaves and stems to determine how much water is required. Then add the proper amount of pesticide. For example, it was determined that it takes 3 L to spray the tree. The label says to use 10 mL/L of water. Mix 30 mL (3 L x 10 mL/L) of pesticide in 3 L of water.
9. When the pesticide label says that the product should be applied `to the point of runoff', apply the spray until it drips off the leaves and runs down the branches and stem. This method is used only with ornamentals, not food plants.
10. Thoroughly rinse the sprayer before storing it upside down and open.

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Granular or Dust Applications

Granular and dust formulations of pesticides do not require mixing and often come in convenient ready-to-use packages. Rates for granular or dust formulations are expressed in several different ways.

The label may recommend a pesticide rate based on the length of a row. For example, a label may specify using 40 g of the formulation on a row 10 m long. If the row is 5 m long, apply half that amount of pesticide (in this case 20 g).

Recommended rates of granular or dust formulations may be based on a given area. For example, a label may specify using 300 g/100 m2. To determine the amount of pesticide that will be required:

1. Calculate the area to be treated by multiplying the length by the width
   (e.g., Area = 2 m x 5 m = 10 m2).
2. Carefully calculate the amount of pesticide needed for this area as follows: Recommended rate x Area to be treated = 300 g/100 m2 x 10 m2 = 30 g/100 m2
3. Apply the calculated amount of pesticide evenly over the area.

If a fertilizer type of spreader is used to apply granules on a lawn, first measure the rate of output of the spreader. To do this:

1. Either attach a plastic bag onto the spreader or put a piece of paper or plastic on the ground to catch the granules. This piece should be at least as wide as the spreader and 2 m long. A longer piece of plastic or paper will help to determine the output more accurately.
2. Put a small, evenly distributed amount of the pesticide in the spreader.
3. Next, determine the correct adjustment for the spreader and the correct walking speed. Keeping the spreader closed, start walking approximately 3 m in front of the paper or plastic sheet. When reaching the sheet, without changing the pace, open the spreader so that the pesticide drops onto the sheet. Close the spreader after walking 2 m (about 2 large steps).
4. Weigh the amount of pesticide on the paper.
5. Measure the width of the spreader and the length covered to determine the area treated with the chemical (width of spreader x length travelled). For example, if the spreader is 1 m wide and the paper 2 m long, an area of 1 x 2 = 2 m2 was treated.
6. Determine the amount (g) applied on 1 m2. Divide the amount in step 4 by the area calculated in step 5. For example, if 200 g were applied on 2 m2, the spreader was dropping 200 /2 = 100 g/m2.
7. Check the label to see if the correct amount of pesticide was applied. If the label reads: 5 kg/100 m2, apply 50 g/m2 (not 100 g/m2). In the example, too much pesticide is being applied. Adjust spreader to a slower output or increase walking speed to reduce the pesticide rate and redo the test run until the output rate is correct. To ensure an even coverage, go over the lawn twice using half the amount of pesticide each time in a criss-cross pattern. First walk lengthways up and down the lawn (Figure A), then walk back and forth across the width of the lawn. For the above example, 25 g/m2 would be applied each time.
8. If the spreader cannot be adjusted, measure the area to be treated, weigh out the required amount of chemical and evenly distribute it by hand using rubber gloves. A metric weighing scale and metric measuring spoons are available and should be purchased. See Imperial to metric conversions.

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Related Links

• Master Gardeners
• Landscape Ontario
• Sprayer calibration
• Metric

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