Applying pesticides requires a high level of skill and knowledge. Increases in the size and complexity of sprayers over the years require even more attention to efficiency, efficacy, and safety. Although each crop requires a slightly different approach to the application of pesticides, some general principles apply to almost all spraying situations.
Here are my top 10 recommendations (not in a particular order) that will make spraying efficient and effective resulting in a higher level of biological efficacy expected from pesticides applied:
1. Select the best nozzle type and size for the job. Although each component of the sprayer plays a role in achieving success in pesticide application, nozzles play the most significant role. Nozzles come in a wide variety of types and sizes. Each type is designed for a specific target and application. Most manufacturers’ catalogs and websites have charts showing which nozzle type is best for a specific job.
Any of the following factors may be the deciding one when selecting the most appropriate nozzle for the job: Sprayer operation parameters (application rate, spray pressure, ground speed); the type of chemicals applied (herbicide, insecticide, fungicide, fertilizers); mode of action of the chemical (systemic or contact) for spray coverage requirement; application type (broadcast, band, directed, air-assisted); risk of spray drift; and specific nozzle or droplet size requirement given on the product label.
Once you determine the best nozzle that will be best for a specific spraying situation, you need to determine the appropriate size of that nozzle that provides the application rates (gal / acre) prescribed by product labels under various operating conditions (spray pressures and travel speeds). More information on selecting nozzle type and size is outlined in Ohio State University (OSU) Extension publication FABE-528, “Selecting the Best Nozzle for the Job.” (here).
2. Carefully read and follow the specific recommendations provided in sprayer operator’s manuals and labels of pesticides applied. Remember, what is required in a label is the law. For example, the labels of 2,4-D or Dicamba herbicides include specific requirements for nozzles and operating pressure ranges.
If you use any other type and size of nozzle and operate them outside the pressure range requirements given by the pesticide manufacturers, you are violating the pesticide label, and therefore the law. Remember, the label is the law!
3. Keep spray drift in mind when spraying. Although complete elimination of spray drift is impossible, problems can be significantly reduced by awareness of the major factors that cause drift, while taking precautions to minimize their influence on off-target movement of droplets. The nozzle you select and the weather conditions at the time of spraying are the two most influential factors affecting generating as well as reducing spray drift.
Keep nozzles as close to the target as possible while still producing a uniform distribution of spray on the target. If weather conditions (wind speed and direction, humidity, temperature, inversions) are not favorable, and there is concern about spray that might result in drift, wait until there is no longer that element of doubt. Extensive information related to factors influencing spray drift, is in OSU Extension publication FABE-525. “Effect of Major Variables on Drift Distances of Spray Droplets.” (here).
4. Maximize pesticide deposit and coverage on the target which may be different part of the crop canopy. For example, when applying a fungicide to manage Fusarium head blight or “head scab,” on small grains, the target is the head, not the leaves. On the other hand, when spraying for soybean sclerotinia stem rot (white mold), the most critical area that needs to be treated with fungicides is where flowering takes place. Nozzle selection has a significant influence on whether or not the droplets reach the specific target location in the canopy.
For example, the twin-pattern nozzles or a single flat-fan nozzle tilted at a forward angle of 30 to 45 degrees down from the horizontal is definitely best for the application of fungicides for wheat head scab. It is, however, the worst setup for soybean insects and diseases, such as aphids and white mold, respectively.
5. Slow down when spraying. Spray coverage is usually improved at slower speeds. The higher the travel speed, the greater likelihood of spray drift.
6. Calibrate the sprayer. A sprayer can only be effective, efficient, and safe if properly checked and calibrated well before the sprayer is taken to the field, and periodically during the spraying season. Some may argue that most sprayers are now equipped with sophisticated rate controllers and ground speed sensors, and calibration is not necessary.
Unfortunately, not all electronic controllers can detect flow rate changes on each nozzle on the boom, and none can detect changes in spray pattern. The primary goal with calibration is to determine the actual rate of application in gallons per acre, and then make adjustments if the difference between the actual rate and the intended rate is greater or less than 5% of the intended rate.
There are several ways to calibrate a sprayer. One easy method is explained in the OSU Extension publication FABE-520, “Calibrating Boom Sprayers.” (here). Be safe. Wear protective clothing, goggles and rubber gloves, and respirators if required on the label, when calibrating the sprayer, doing the actual spraying, and cleaning the equipment.
7. Check uniformity of application. How uniformly the chemical is deposited on the target is as important as the amount applied. Maintain uniform deposition of spray material on across the entire width of the target area. Non-uniform coverage results from using misaligned or clogged nozzles, using nozzles with different fan angles, or from uneven nozzle height across the boom. These common problems result in streaks, untreated areas, or over-application of chemicals.
8. Understand how to calculate the amount of chemical product to mix in the tank. Although your sprayer may be in good condition and calibrated frequently, if the correct amount of chemical is not put into the tank, it can still result in unsatisfactory pest control. Detailed information on how to calculate the proper amount of chemical to add to the spray tank is provided in the OSU Extension publication FABE-530. “How Much Chemical Product Do I Need to Add to my Sprayer Tank.” (here).
9. Take advantage of technological advancements in spray technology, such as GPS, automatic guidance systems, and independent control of nozzles using the PWM (Pulse Width Modulation). Update and upgrade your sprayer with these technologies that can be easily integrated in your existing sprayer.
10. Consider using a sprayer that is equipped with air-assisted boom when coverage in lower parts of the canopy is essential for control of some insects and diseases especially under full, dense canopy conditions, such as soybeans sprayed in late season.
For more information on this topic, please read the OSU Extension publication FABE-532, “Best Practices for Effective and Efficient Pesticide Application.” (here). Don’t hesitate to contact me if you have a specific question that was not addressed in this and other OSU Extension publications I mentioned in this article.