Know your EXACT spray pressure for success

Erdal Ozkan Applied Engineering

Pesticides are getting more expensive. To get the most out of them requires more precision and less waste in application of active ingredients in pesticides. Applying pesticides at the right pressure is essential for successful pest control.

There are many things that affect the end result (efficacy) from a pesticide application. The most obvious ones are: careful scouting (knowing exactly what the problem is); selecting the best pesticide to take care of the problem; applying the right amount of pesticide per acre uniformly on the target; keeping as much of the pesticide applied as possible in the intended area of application; weather conditions during the application; and timing of application.

Other than the weather conditions, you can control all the other factors mentioned above. Let's focus on one of these factors for now: keeping the pesticide applied in the application area with maximum deposit on the target. So, how do we achieve this since we have no control over the weather, specifically wind? The answer: the size of the droplets.

Nozzle selection

Nozzles are a key factor in droplet size. They also help us achieve a precise flow rate and the desired spray pattern. In general, smaller droplets are more effective, especially for insecticide and fungicide applications. However, small droplets are highly susceptible to spray drift, increasing the risk of losing them.

Pressure gauge testing

Pressure gauges on sprayers are there for one reason: measure the actual pressure. They are important accessories of a spraying system because pressure affects both the amount of liquid being sprayed and droplet size. A malfunctioning pressure gauge may result in over or under application of pesticides, and significant changes in droplet size.

Increasing pressure causes an increase in the number of small droplets, and in the flow rate. Decreasing pressure does the opposite, increasing droplet size and reducing flow rate. For instance, increasing the pressure by a factor of 4 doubles the flow rate.

To accurately regulate spray pressure, it first has to be measured. Use a pressure gauge with a range at least twice the expected operating pressure. A pulsation damper protects and increases the life of a pressure gauge and smoothes pressure pulsations, which makes reading the gauge much easier.

There is usually a pressure drop in the spray line between where the pressure regulator valve is located and the nozzles. Therefore, pressure gauges should be located as close to the nozzles as possible, and the pressures at the nozzles should be checked at least once to determine the magnitude of the pressure drop.

Having an accurate pressure gauge is essential to proper calibration of a sprayer. Therefore, compare the readings from your pressure gauge periodically with the readings from another calibrated gauge. H. Zhu and his co-workers at The Application Technology Research Unit of USDA-Agricultural Research Service in Wooster, have developed a portable device that can be used to check the accuracy of pressure gauges on sprayers. The device (see photograph) is a revised version of a lightweight Model T-621 hydraulic pressure pump from AMETEK Measurement & Calibration Technologies. (Contact 727-536-7831 or calinfo.us@ametek.com for details on the Model T-621.)

The testing unit consists of a hand pump, a factory calibrated gauge, a small water reservoir and a port for the gauge that is to be tested (shown on the left in the photograph). Remove the gauge from the sprayer and screw it onto the port on the side of the tester. Then squeeze the handle and read the pressure on both gauges. If the pressure readings are the same, your gauge is in good condition. If not, replace the bad pressure gauge with one that is accurate to maintain the droplet size and the flow rate desired.

Getting the most out of pesticides depends on many factors. Pressure is only one of these factors, but an important one.

For the lack of a good $40 pressure gauge you could lose thousands of dollars because of lower crop yields. And drift-related litigations could reach hundreds of thousands of dollars. I suggest you avoid this risk, and check your pressure gauges now.

Erdal Ozkan, professor and Extension agricultural engineer, can be reached at 614-292-3006 or ozkan.2@osu.edu. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research and Development Center, and the College of Food, Agricultural and Environmental Sciences.

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