By Erdal Ozkan, Agricultural Engineer
This is the time of the year you must complete shopping for nozzles because the spraying season is just around the corner. Although nozzles are some of the least expensive components of a sprayer, they hold a high value in their ability to influence sprayer performance.
Nozzles meter the amount of liquid sprayed per unit area, controlling application rate, as well as variability of spray over the width of the sprayer boom. Nozzles also influence droplet size, affecting both target coverage and spray drift risk. Nozzles come in a wide variety of types and sizes. The best nozzle for a given application will maximize efficacy, minimize spray drift and allow compliance with label requirements, such as application rate (gallons per acre) and spray droplet size.
Selecting the best nozzle requires careful consideration of many important factors including: sprayer operation parameters (such as application rate, spray pressure, travel speed); type of chemical sprayed (herbicides, insecticides, fungicides); mode of action of chemicals (systemic, contact); application type (broadcast, band, directed, air assisted); target crop (field crops, vegetables, vineyard, shrubs and trees, etc.); and spray drift risk. The Ohio State University Extension Publication, “Selecting the Best Nozzle for the Job,” gives step-by-step guidelines for selecting the most appropriate spray nozzle for a given application situation.
There is a large type of nozzles to choose from. Each nozzle type is designed for a specific type of target and application. For example, a nozzle designed for broadcast spraying is not good for spraying pesticides over a narrow band. While one nozzle may be best for a given situation, it may be worst choice for another.
At Ohio State University we have conducted field experiments to determine which nozzles to choose for two different application situations: soybean diseases, such as rust and white mold, and wheat diseases, such as head scab and stem rust. We included 6-8 different nozzles in the experiments. We found out that while a twin-fan pattern nozzle was best for controlling wheat head scab, the same nozzle turned out to be the worst choice to protect soybeans against rust and white mold when the soybean canopy is tall and dense.
So before buying the nozzles and putting them on the boom, check the nozzle manufacturers’ catalogs, which have charts showing which nozzle type will be best for a specific job. Check the websites of nozzle manufacturers to reach their catalogs.
Once you determine the type of a nozzle you need to buy, you also must buy the right size of that nozzle, which will satisfy the application rate (gallons per acre or gpa) you wish to use as you do your spraying at different travel speeds. Nozzle catalogs are filled with tables and charts showing application rates, given a nozzle’s flow rate (gallons per minute or gpm) delivered at various pressures (psi) and travel speeds (mph). These tables are useful tools for selecting the appropriate nozzles, pressure and speed to spray chemicals at application rates prescribed by product labels.
However, the charts are only for a limited number of travel speed and nozzle spacing situations. There may be situations where the charts will not provide information associated with your sprayer setup (nozzle spacing) and operating conditions (travel speed and spray pressure). The apps developed by most of the major nozzle manufacturers can provide you the exact nozzle flow rate required for any given set of application parameters, and identify a specific set of nozzle recommendations for the given application parameters.
To find these apps, simply visit the app store in your smartphone or tablet and do a search under “Spray Nozzle Calculator,” or some other keywords related to nozzle size selection. You may also want to do a search under the name of the nozzle company from which you are interested in buying the nozzles. However, some apps are not user friendly and sometimes do not take into account the droplet size requirements when recommending nozzles.
Although these apps and tables in catalogs may expedite the nozzle size selection process, it’s best to understand the procedure and math nozzle manufacturers use to generate the values and recommendations they come up with in their catalogs and apps. By following the steps mentioned in the new OSU Extension publication mentioned above (AEX-528) you will be able to determine the exact nozzle flow rate (gpm) required for your spray application parameters. Once the exact nozzle flow rate is determined, you can then look at the catalog to select the nozzle that will provide you the flow rate at a practical pressure setting.
Keep Several Types of Nozzles on the Boom
Remember that one specific type of nozzle will not be best for all applications. For this reason, it’s best to have several types and sizes of nozzles on the boom so that you can switch to the “best” nozzle choice for a given spraying job. There are various types of sprayer components and setups (see photos to the right) you can buy to configure your boom so the new set up allows you to easily switch from one nozzle to another instantly.
Keep Spray Drift in Mind
One of the major problems challenging pesticide applicators is spray drift, which is defined as movement of pesticides by wind from the application site to an off-target site. Drift is influenced by many factors, which are discussed in detail in OSU Extension publication Bulletin 816.
Equipment, especially the nozzles, used to spray pesticides play a significant role in generating — as well as reducing — spray drift. In nozzle catalogs, you can see a number of different nozzles of the same type, in terms of spray pattern. For example, one can find nozzles within the same “flat-fan” category classified as “low-drift.” Research conducted at Ohio State and elsewhere clearly indicates that nozzles labeled as “low-drift” significantly reduce spray drift. If drift is, or becomes a concern, it may be best to switch from a conventional flat-fan nozzle to a “low-drift” flat-fan nozzle with the same flow rate. Therefore, it’s best to have more than one type of a “flat-fan” pattern nozzle on the boom.
Some Final Thoughts
Nozzles are typically the least costly items on a sprayer, but they play a key role in the final outcome from a spraying job: achieving maximum efficacy from the pesticide applied while reducing the off-target (drift) movement of pesticides to minimum. Pesticides work well if the rates on labels are achieved during application. This can be achieved only if the right nozzle type and the proper size of the nozzles are on the sprayer, and the sprayer is operated properly.
Although the apps and tables in catalogs may expedite the nozzle size selection process, it’s best to understand the process and the math nozzle manufacturers use to generate the values listed in the tables, and to generate nozzle recommendations in their Apps. This procedure, explained in this new OSU Extension Publication (AEX-528) hopefully will help you to determine the exact nozzle flow rate (gpm) required for your spray application parameters, while highlighting some other important parameters such as spray pressure, droplet size, spray coverage on the target, and drift, all of which should be given serious consideration when selecting the best nozzle for a spraying job.