Calibration of Equipment for Applying Fertilizers and Pesticides to Turfgrass

on by Harrell's in Golf, Turf & Landscape

by Jeff Higgins, Ph.D.

Precise calibration and application of pesticides and fertilizers is imperative in today’s political climate with concerns for the preservation of our environment, conservation of resources, and costs associated with pesticides and fertilizers. Accurate calibration of sprayers and spreaders allows precise application of either pesticides and/or fertilizers at proper recommended rates in accordance with local, state and federal regulations. The recommended use rates listed on product labels have been determined through extensive research and testing to be the most effective to accomplish the task for which these products are being applied. Using less of the product may not accomplish that purpose and may make a second or repeat application necessary, which is more expensive than doing it right the first time. Using more of the product than recommended may cause damage and definitely will be more expensive. The PERFORMANCE of any product can be no better than the manner in which it was applied! In addition, proper calibration of application equipment is now a legal requirement when applying Restricted Use Pesticides.

You can spend hours in the field calibrating your sprayer and spreader to achieve accuracy, but your efforts are wasted if you don’t know how many products to put in the tank. Surveys have shown that approximately 40% of the applicators fail to add the correct amount of product to the tank in liquid pesticide applications. As a turfgrass manager or homeowner, how often have you got in a hurry to get something put out that you just guessed or estimated the proper spreader setting or volume of a product to add to the sprayer? Guessing, estimating, and carelessness must be eliminated from pesticide and fertilizer applications!

Today, more than ever, the application rate and uniformity of application are as important as the pesticide or fertilizer selected for use. Calibration of application equipment, whether sprayer or spreader, takes little time, but requires knowledge of a few principles. However, the effort put forth into the calibration of this equipment will be returned many fold.

The objective of precise calibration of sprayers and spreaders is accurate and efficient distribution of pesticides and fertilizers. Today, it is a violation of federal laws to apply pesticides at rates other than those specified on the product label. Applicators are subject to fines, in addition to the liability for any damage caused to plants and/or the environment for the careless application of pesticides and fertilizers. Therefore, calibration of application equipment should be of foremost importance to you as a turfgrass manager!

Liquid Applicators (Sprayers)

Sprayers are used to apply pesticides and water-soluble fertilizers. Hand held backpack sprayers, hose-end sprayers, and boom sprayers are all used to apply these types of products. All of these types of liquid sprayers operate on the same basic principles. However, before using these sprayers, they should be properly calibrated.

Backpack or Hand-Pressurized Sprayers

One to three gallon backpack sprayers with a single hand held nozzle are generally used to spray ornamental plants with fungicides and insecticides, to spot treat weeds or to chemically edge along fences and buildings. Recommendations for mixing and spraying these products with a backpack sprayer usually suggest adding a specific weight or volume of product per gallon of water and spraying the foliage to the point of run-off. Such sprayers work well for that type of chemical application.

Broadcast applications to turfgrass with the backpack sprayer are not recommended without a pressure regulator to maintain a constant pressure. In combination with a compressed air or CO2 cylinder and a pressure regulator, the backpack sprayer can be used for broadcast applications of chemicals.

To calibrate a backpack sprayer for broadcast applications, the operator must determine the volume of water per 1,000 square feet that the sprayer applies at a given pressure and speed. For example, an operator determines that at 30 psi he can cover 200 square feet with a quart of water walking or moving at a comfortable pace. Thus, the operator will be applying 5 quarts of water per 1,000 square feet. He may want to decrease the pressure slightly, walk or move at a slightly faster pace or change nozzles so that he will be applying 1 gallon of water per 1,000 square feet. Then, if he has a 2-gallon sprayer, he adds enough product to cover 2,000 square feet and fills the sprayer to the 2-gallon mark.

Another procedure to calibrate a hand held backpack sprayer is to determine the effective swath (width) the operator makes as he walks with the sprayer, and use the following procedure to calculate the volume of water applied per 1,000 square feet.

  1. Measure the effective spray width (swath) in feet. This is most effectively measured on concrete or dry dirt where the spray pattern is clearly visible and can be measured.
  2. Refer to Table 1 to determine the length of the calibration course.
  3. Determine the time required to walk the length of the calibration course.
  4. Catch the water output from the nozzle(s) for a time equal to that required to walk the calibration course.
  5. Measure the volume of water caught in pints. The pints of water caught equals the gallons of water applied per 1,000 square feet. To adjust the volume of water applied, the operator may change the nozzle size, walking speed (pace), or operating pressure of the sprayer.

Table 1. Calibration Course Length for Hand Held Sprayer Based on Effective Spray Width

Effective Sprayer Swath Width (in Feet) Length of Calibration Course (in Feet)
2 62.5
3 42
4 31
5 25
6 21
7 18
8 15.5
10 12.5

Calibration Example: An operator using a hand held sprayer with a single nozzle covers a spray width (swath) of 4 feet. Using information from Table 1, the operator measures out a calibration course that is 31 feet in length. The operator measures the time it takes to walk the calibration course with the sprayer. The time required was 60 seconds. The operator then catches the water volume output of the sprayer for 60 seconds. A total of 12 ounces of water was collected during the 60-second time frame. To convert the 12 ounces to pints, divide by 16 (16 ounces = 1 pint). Thus, the operator collected 0.75 pints (12 divided by 16) over the calibration course. Therefore, this is equivalent to 0.75 gallons of water per 1,000 square feet. When the operator uses the sprayer to apply a product, they must apply enough product to spray 1,000 square feet for each 0.75 gallons (3 quarts) of spray solution or water.

Hose-end Sprayers

Hose-end sprayers are used to apply fungicides, insecticides, herbicides, and liquid fertilizers. Since hose-end sprayers operate off of water pressure, they need to be calibrated at the water outlet from which they will be operated. Hose-end sprayers should be calibrated on concrete or dry pavement where the spray pattern is clearly visible.

Add either a pint or quart of water to the reservoir of the hose-end sprayer, open the water outlet and spray the concrete or pavement uniformly until the sprayer reservoir is empty. Calculate the area that is covered or wet by the sprayer by multiplying the width of the spray pattern by the length of the wet surface. Then, add enough product to cover the area by a quart of water, fill the reservoir to one quart and make the application.

Calibration Example: A homeowner wants to apply a herbicide to their lawn with a hose-end sprayer. The homeowner determines that 1 pint of water will cover 300 square feet at a normal walking pace. The herbicide label recommends a rate of 4 ounces of product per 1,200 square feet. Thus, the homeowner adds 2 ounces of the herbicide and fills the sprayer reservoir to 1 quart (2 pints) with water (2 X 300 square feet = 600 square feet). Each quart of the sprayer reservoir should cover 600 square feet of lawn.

Boom Sprayers

Boom sprayers are used for broadcast applications of pesticides and fertilizers to large turfgrass areas, such as fairways. Boom sprayers can be precisely calibrated to apply products uniformly at a recommended rate. As with other sprayers, operating pressure, nozzle size and spacing, and operating speed determine the volume of water applied per 1,000 square feet or per acre. For most products, 1 to 2 gallons of water per 1,000 square feet is a desirable application rate. For some herbicides, the application or delivery rate may be only 0.5 gallon of water per 1,000 square feet. Remember the higher the spray volume of water applied, the more frequently the spray tank must be refilled.

To calibrate a boom sprayer, the operator must determine the volume of water per 1,000 square feet or per acre that the sprayer applies at a given pressure and speed. There are several methods to measure this volume. The following procedure simplifies the operation and can be used for most boom sprayers.

  1. Measure the distance (in inches) between nozzles on the boom.
  2. Refer to Table 2 for the length of the calibration course.
  3. Measure out the length of the calibration course.
  4. Determine the time required to drive or walk the calibration course.
  5. While the sprayer is stationary, collect the water from one nozzle for the time that was required to drive or walk the calibration course. The sprayer must be maintained at the operating pressure to be used for the application.
  6. Measure the volume of water caught in ounces. The number of ounces equals the gallons of water applied per acre.
  7. Adjust the pressure, speed, or nozzle size to achieve the desired volume. Repeat the procedure until you are close to the desired volume.
  8. Check the volume of several nozzles. The volumes from different nozzles should be within 10% of each other.

Table 2. Calibration Course Length for Boom Sprayers Based on Nozzle Spacings.

Nozzle Spacing (Inches) Length of Calibration Course (in Feet)
12 340
14 291
16 255
18 227
20 204
25 163
30 136
40 102
60 68

Calibration Example: A golf course superintendent wants to apply MSMA herbicide to a fairway to control escape crabgrass. He purchases Daconate 6, which is a MSMA formulation that contains 6 pounds of MSMA (active ingredient) per gallon. The label recommends applying 3 pounds of MSMA per acre in 50 gallons of water. The superintendent has a 12-foot sprayer boom with nozzles spaced 18 inches apart with a 50-gallon tank. Using Table 2, he marks off a 227 feet calibration course, adjusts the pressure to 20 psi, and drives the length of the calibration course. He determines that it takes 65 seconds to travel the 227 feet. He then collects the water output from one nozzle for 65 seconds. The volume caught is found to be 35 ounces or 35 gallons of water per acre. Thus, he increases the operating pressure to 25 psi and catches the nozzle again for a 65-second duration. This time, he catches 48 ounces or 48 gallons per acre. He then measures the water volume output for all of the nozzles and gets a range between 46 and 53 ounces or gallons per acre. All of the nozzles are within the 10% range; therefore, the sprayer is calibrated at 50 gallons of water per acre. The superintendent then adds 2 quarts of Daconate 6 (3 pounds of MSMA) to the tank and fills it to 50 gallons. His tank should then cover or spray one acre.

Granular Applicators (Spreaders)

The selection of equipment to apply granular fertilizers or pesticides is less extensive and less flexible than that available for liquid applications. Granular spreaders are used for applying pesticides, granular fertilizers, and for turfgrass broadcast seeding and overseeding. Numerous disadvantages exist for granular application equipment. Because of the inability to adjust carrier volume (as in liquid applications), individual calibration is required for each granular product and the actual product must be used during calibration. Also, fewer products are available in granular form than in liquid form. Some granular products, especially postemergence herbicides, can be less effective than their liquid counterparts. In spite of these disadvantages, many turfgrass managers utilize only granular products. Granular application, however, has numerous advantages over liquid applications. One of which is limited applicator exposure during the handling, mixing, and application of the granular products versus liquid applications.

The calibration of granular application equipment is somewhat similar to that of liquid application equipment, except for several subtle differences. Granular pesticides are formulated with an inert carrier, so the pesticide concentration, as well as fertilizer concentrations, are fixed and cannot be adjusted. This requires that calibration be performed for every different granular product used and the actual fertilizer or pesticide granules are used during calibration. Each granular product will have a suggested spreader setting for specific brands of spreaders. This is only a starting point! Spreaders should still be calibrated before each application. Relative humidity can also affect the dispersion of granular products. It is recommended that calibration be repeated under relative humidity conditions similar to the conditions expected or present during application.

Granular applications are used for the distribution of dry fertilizer products and granular formulations of pesticides, such as fungicides, herbicides, and insecticides. There are basically two types of granular applicators: (1) drop spreaders (gravity flow) and (2) rotary or centrifugal spreaders.

Drop Spreaders

Drop spreaders operate by “dropping” or distributing granular products via gravity flow between the wheels of the spreader as it is pushed or pulled across the turfgrass. The rate of application is controlled by the width of the opening at the bottom of the drop spreader and the walking speed of the applicator.

To calibrate a drop spreader, the operator must determine the amount of product or granular material that is dispersed per unit area at a specific spreader setting and constant speed. The operator that will make the actual application should be pushing the spreader or driving the tractor, etc. so that the speed during the actual application is the same as the speed used during the calibration.

Some drop spreaders have a calibration pan or tray that attaches beneath the opening at the bottom of the spreader. In this case, the operator simply connects the pan or tray to the spreader, fills the spreader with the actual granular product, and makes a pass over a given distance with the spreader open. The collected product in the pan or tray is then weighed. The rate of application per given area can then be calculated (amount of product collected per given distance) by dividing the amount of product collected by the given distance. This rate of application can then be easily converted to pounds product per 1,000 square feet or acre. In the absence of a calibration pan or tray, the operator must either collect the granular product over a clean surface such as plastic or concrete floor. The product can then be collected and weighed to determine the amount of product applied or the loss of weight from the spreader when making a pass over a given area.

Another method to calibrate a drop spreader does not involve pushing or pulling the spreader. Instead, the diameter of the wheel is measured in feet and the length or given distance then determined by the number of revolutions that the wheel is turned to collect the product. For example, the wheel diameter for a drop spreader was 2 feet and the width (swath) was 4 feet. Therefore, if the spreader wheels were turned for a total of 20 revolutions, then the distance would be 40 feet. The granular product can be collected while the wheels are being turned. Then, weigh the amount of product collected and calculate the rate of application over the given distance of 160 square feet (4 feet swath X 40 feet = 160 square feet).

Calibration is a “trial and error” process and must be repeated until the desired results are obtained. If initially the spreader applies too much product, then the setting or opening is reduced and vice versa, if the setting applies too little product, then the setting or opening is increased.

Measurements required to calibrate a drop spreader include the distance the operator covers and the weight of the product applied. Obviously, a scale will be required to weigh the granular products.

Calculations should be kept simple and consistent to reduce the chances of inducing error. If the recommended rate for a given product is expressed in ounces per 1,000 square feet, then measure the required distance needed to provide 100 or 200 square feet for ease of conversion to 1,000 square feet. For example, if the spreader has a 3 feet width (swath), then measure 33 and 1/3 feet or 66 and 2/3 feet for 100 or 200 square feet, respectively. You can refer to Table 3 to determine the appropriate distance to measure for a given spreader width (swath).

Table 3. Distance to Measure to Cover 100 Square Feet or 1/100 of an Acre.

Width of Spreader (in Feet) Distance to Measure to Cover Specified Area (in Feet)
100 Square Feet 200 Square Feet
2 50  
3 33 1/3  
4 25  
6 16 2/3 72 ½
8   54 ½
10   43 ½
12   36 1/3

After several passes over the distance to establish a consistent and practical speed, load the spreader with the actual product to be applied and make a pass over the starting and ending lines that mark the distance. Be certain to travel at a consistent speed when crossing the starting and ending lines. Do not begin walking at the beginning line and stop at the ending line. While walking at a constant speed, simply open the spreader at the beginning line and close the spreader at the end line. Collect the product during the pass from the calibration pan or tray or from the surface between the beginning and ending lines. Weigh the product in ounces or pounds. Use one of the following equations to calculate the rate of application and compare that to the targeted rate.

(1) (ounces product collected per 100 square feet divided by 16) X 10 = Lbs product per 1,000 square feet

(2) (ounces product collected per 200 square feet divided by 16) X 5 = Lbs product per 1,000 square feet

Calibration Example: A lawn care operator wants to apply a 15-5-9 fertilizer at a rate of 10 pounds per 1,000 square feet using a 3 foot drop spreader. He measures a distance of 33 and 1/3 feet based on Table 3 and marks the starting and ending lines with stakes. After establishing a consistent walking speed, he loads the spreader, moves the spreader setting to “5”, attaches the calibration tray, and prepares to make a pass along the calibration distance. He begins walking several feet before the starting line stake so that he is “up to speed” when opens the spreader at the beginning line stake. He closes the spreader at the ending line stake as he takes several steps pass. The operator collects the product from the tray and weighs the contents. He finds that 12 ounces of the 15-5-9 fertilizer were collected. Using equation (1), he calculates that 7.5 pounds of 15-5-9 were applied per 1,000 square feet. Therefore, he increases the spreader setting to “6.5” and makes another pass across the trial path. This time he collects 16 ounces of 15-5-9. Using equation (1), he calculates that 10 pounds of 15-5-9 per 1,000 square feet.

It is important to recognize that the operator must calibrate the spreader for each formulation or brand of granular product used. A different brand of 15-5-9 fertilizer may have granules of different particle sizing or density, thus requiring a different spreader setting.

Rotary or Centrifugal Spreaders

The same calibration procedure is followed for rotary or centrifugal spreaders; however, it may be more convenient to weigh the product remaining in the spreader instead of trying to collect the widely dispersed product. Thus, the operator would weigh the product that was placed in the rotary spreader and subtract the product remaining in the spreader after a trial pass to determine the amount of product applied.

The swath width of a rotary or centrifugal spreader must be measured for each product to be applied since it will vary according to the particle sizing and density of the individual particles. The swath width is controlled by the speed of the centrifugal disk and can be altered by ground speed in the case of ground-driven spreaders or motor speed in the case of powered centrifugal spreaders. Coverage for these spreaders is, therefore, variable and must be determined for the speed to be used in actual pesticide or fertilizer application.

To determine the swath width of rotary spreaders, place a series of collection trays on a 1-foot spacing perpendicular to the line of travel of the spreader. These containers can be any type of box, pie tins or similar container. It is recommended to find some calibration trays that are 1 square foot in their dimension. Each container used, however, should be of the same dimensions.

Load the rotary spreader with the actual granular product to be applied and set the opening on a medium setting. Run the spreader, at the speed to be used in actual operation, over the collection trays with the spreader open.

Check the collection trays for the granular product. By observing the amount and distribution of the product in the collection trays, a reasonable estimate of spreader swath can be made. If the product in each container is also weighed, distribution can be checked and, if necessary, adjustments made. Coverage is determined by multiplying the swath width by the calibration distance. You may use Table 4 to determine the calibration distance to travel. Since rotary spreaders cover a relatively larger area, a 250 to 500 square feet trial area may be used instead of the 100 square feet recommended for drop spreaders. For example, a rotary spreader with a swath width of 10 feet traveling a distance of 25 feet has a coverage of 250 square feet (10 feet X 25 feet = 250 square feet).

Table 4. Distance to Measure to Cover 250 Square Feet or 500 Square Feet.

Spreader Swath Width (in Feet) Distance to Measure to Cover Specified Area (in Feet)
250 Square Feet 500 Square Feet
5 50  
6 42  
7 35 ½  
8 31  
9 28  
10 25 50
12   42
13   35 ½
16   31
18   28
20   25

Next, the amount of product required to deliver the rate of pesticide or fertilizer is required. For example, if the labeled rate of a product is 180 pounds of product per acre. To facilitate calibration and avoid unnecessary waste of pesticide or fertilizer, this quantity is reduced to a much smaller area. This is done by setting up a ratio or proportion problem and solving for the unknown.

In this case, X equals 1.03 pounds (43,560 X = 180 X 250 therefore X = 1.03). When X is solved correctly, this is the amount of product required to deliver 180 pounds per acre, based on the previously determined coverage.

To calculate the amount of product applied per 1,000 square feet or per acre, use one of the following equations:

(3) (ounces product applied per 250 square feet divided by 16) X 4 = Lbs product per 1,000 square feet

(4) (ounces product applied per 500 square feet divided by 16) X 2 = Lbs product per 1,000 square feet

(5) (ounces product applied per 500 square feet divided by 16) X 87 = Lbs product per acre

Calibration Example: An operator has a rotary spreader that covers a 6-foot wide swath when applying a granular fungicide. She wants to apply the product at 7.5 pounds per 1,000 square feet of turfgrass. She measures a trial swath that is 42 feet long based on Table 4 and puts 5 pounds of product into the spreader and makes a pass across the trial path. After making a pass, she weighs the product remaining in the spreader and determines that it is 3.9 pounds. Using equation (3), she makes the calculations and finds that the application rate is 4.4 pounds of product per 1,000 square feet. Since her target rate is 7.5 pounds per 1,000 square feet, she has the option of lowering the spreader setting and making twice as many passes over the turfgrass area or increasing the setting and making a single pass. In either case, she must adjust the spreader setting and make more calibration runs.

To avoid skips or overlaps at the full rate of product, it is recommended to calibrate the spreader to apply ½ the recommended use rate and making two passes across the turfgrass at right angles to one another or parallel to one another at intervals of ½ of the swath width. This will insure better distribution and uniformity of the granular product over the treated area. In this example, it would require applying 3.75 pounds of product per 1,000 square feet per pass at intervals of 3 feet.

Area Calculations

Given recent decisions by government agencies, the importance of proper calibration of application equipment has become more important. To help do this, one must be able to calculate area correctly.

Field measurements of turfgrass areas may be made in several different manners. Geometric figures are one good method to determine a given area.

Area Measurements

(1) Square or Rectangle

  • Area = Length X Width

(2) Triangle

  • Area = ½ X Base X Height

(3) Circle

  • Area = p X Radius X Radius, where p is a constant and equal to 3.14 and Radius equal to ½ the diameter of the circle

(4) Irregular Shapes

  1. Measure the longest axis of the area (length line)
  2. At every 10 feet along the length line, measure the width at right
  3. angles to the length line
  4. Total all widths and multiply by 10 (10 feet intervals)

Conversion Factors

Area Measure

  • 1 Acre = 43,560 Square Feet = 4,840 Square Yards
  • 1 Square Yard = 9 Square Feet
  • 1 Square Foot = 144 Square Inches
  • 1 Linear Foot = 12 Linear Inches

Fluid Measure

  • 1 Gallon = 4 Quarts = 8 Pints = 16 Cups = 128 Ounces = 3,785 Milliliters (ml)
  • 1 Quart = 2 Pints = 4 Cups = 32 Fluid Ounces = 946.25 Milliliters (ml)
  • 1 Pint = 2 Cups = 16 Fluid Ounces = 473.125 Milliliters (ml)
  • ½ Pint = 1 Cup = 8 Fluid Ounces = 236.56 Milliliters (ml)
  • 1 Ounce = 2 Tablespoons = 29.76 Milliliters (ml)
  • 1 Tablespoon = 15 Milliliters (ml)

Weight Measure

  • 1 Pound = 16 Ounces = 453.6 Grams (g)
  • 1 Ounce = 28.35 Grams (g)
  • 1 Tablespoon = 3 Teaspoons = 15 Grams (g)
  • 1 Teaspoon = 5 Grams (g)
  • 1 Mile per Hour (MPH) = 88 Linear Feet per Minute