Rates reported for tobacco in the Ontario Crop Protection Hub are for broadcast applications. However, in many cases for tobacco, a banded application may be preferred. This section describes how to calculate sprayer output and product rate for a banded herbicide application. This procedure can also be used for banded applications of most tobacco pest control products, except fumigants. For fumigants, see the product labels for banded rates or calculations.
Where crops are planted in rows, growers can save on chemical costs and reduce the chances of drift by performing banded applications. Banded application is applying the product in parallel bands corresponding to the crop rows, unlike broadcast application where the entire area receives product, as illustrated in Figure 1. This means only a portion of the field receives treatment, so the total amount of product applied per hectare should be less for banded than for broadcast applications.
Banded applications can be adapted to fit multiple situations, e.g., applying herbicides right over a crop during planting, both for pre-emergent or post-emergent crops. It can also mean carefully spraying between the rows to control weeds in an established crop.
It is not uncommon for mistakes to be made in calculating product rates for banded spraying, and these can be costly errors. Too little means poor control, and too much means wasted product and possible crop injury. Avoid using the wrong rate by following these steps for herbicide application.
Step One: Establish the Broadcast Product Rate and Sprayer Output
Product labels often list broadcast product rates and sprayer outputs. With banded applications, the rate applied to the treated area (i.e., the sprayed bands) is the same as the label rate, but the total amount of pesticide used per hectare is less. In the example discussed below, the label recommends a broadcast product rate of 5 L of herbicide in a sprayer output of 300 L of water/ha.
Step Two: Establish Sprayer Settings
a) Select a forward speed that is safe, gives a reasonable work rate and does not compromise coverage. Set two stakes 50 m apart in the field that is going to be sprayed and time how long it takes to drive the 50 m at this speed. In the example discussed below, a sprayer moving at 8 km/h should traverse 50 m in 22.5 seconds.
b) Select a band width that completely covers the target row and some of the adjacent area where weed control is desired. Measure band width along the ground for soil-applied pesticides and toward the top of plants for post-emergence chemicals. The illustration below shows an example of band width application. For the in-row application, bands are 30 cm wide on 90-cm centres.
Step Three: Establish the Banded Sprayer Output
Use the following formula to convert the broadcast sprayer output into the banded sprayer output:
(Band Width in cm/Row Spacing in cm) x Broadcast Sprayer Output (L/ha) = Banded Sprayer Output
For example, using the broadcast sprayer output from Step One, we arrive at the following banded sprayer output:
(30-cm Band Width/90 cm Row Centres) x 300 L/ha Broadcast Sprayer Output = 100 L/ha Banded Sprayer Output
Mix the labelled product rate of 5 L of herbicide in 300 L of water. With a banded sprayer output of 100 L/ha, there will be enough spray mix to apply to 3 ha.
Another way to consider this step is to calculate how much product will be required per hectare. When a product label gives a broadcast rate, it can be converted to a banded rate. The following formula assumes the broadcast rate in kilograms per hectare:
(Broadcast Rate in kg/ha x Band Width in cm) / Row Spacing in cm= Banded Rate in kg/ha
Step Four: Establish the Nozzle Output
Use the following formula to determine what each nozzle should emit. Remember, sometimes multiple nozzles are used to spray a single band.
(Banded Sprayer Output in L/ha x Band Width in cm) / (20 x number of nozzles per band) = Single Nozzle Output in mL
Continuing with the example, assume it takes one nozzle to create a single band on a row. Therefore:
(100 L/ha Banded Sprayer Output x 30 cm Band Width) / (20 x 1 Nozzle per Band) = 150 mL output per nozzle
Step Two showed that it took 22.5 seconds to travel 50 m. Use the following formula to determine nozzle output per minute:
(60 sec x Nozzle Ouput in mL) / Time to Travel 50 m in sec = Nozzle Ouput in mL/minute
Continuing with the example:
(60 sec x 150 mL)/22.5 sec = 400 mL/min
Using a nozzle manufacturer’s catalogue, select a nozzle tip that gives the desired spray quality and use the rate charts to determine the nozzle output for the sprayer pressure and ground speed.
Step Five: Calibrate the Sprayer
Calibrate the sprayer and make minor adjustments until the nozzle discharge per minute equals the desired spray volume. For example, if the sprayer output is higher than desirable, a sprayer operator can swap to nozzles with less output, reduce operating pressure (as long as it remains within the nozzle’s range) or increase the ground speed, although this last method may compromise coverage. If the sprayer output is lower than desired, a sprayer operator can swap to nozzles with higher output, increase operating pressure (as long as it remains within the nozzle’s range) or reduce the ground speed, although this last method will increase the time it takes to spray.
For more information, see these online resources:
Calculating banded applications:
http://sprayers101.com/sprayer-math-for-banded-applications/
Banded spraying in potatoes:
www.agrireseau.net/phytoprotection/documents/BandedPesticidePotatoes.pdf
Online banded spray calculator (Commercial):
http://teejet.it/english/home/calculator/calibration-calculator.aspx
Online banded spray calculator (OMAFRA):
ontario.ca/crops, search for “sprayer calibration calculator”
Online sprayer resource:
www.sprayers101.com