In a world where application efficiency goes hand-in-hand with on-target spraying, applicators need to consider many variables.
The application of crop protection products is considered an integral and viable part of a total integrated pest management (IPM) program, provided that the application itself is made in a safe and efficient manner, maximizing pest efficacy while minimizing impact on the environment. Off-target particle drift is considered one major source of application inefficiency negatively impacting yields, and increasing unnecessary costs.
Particle drift can also have detrimental impacts on the environment. Injury to susceptible vegetation, wildlife, people and contamination of water supplies may occur. Every application is a balance between the need to control the targeted pest and the need to minimize drift.
Application 1.0 occurred when the primary focus was on controlling the targeted pest. Application 2.0 arrived when drift became an increasingly pressing issue and thus the focus of application technologies and procedures. We are now entering the period of Application 3.0, where applicators are realizing they must find a suitable balance between both application goals.
Reducing Driftable Fines
Over the last several years, there has been an increased emphasis by nozzle manufacturers to engineer spray nozzles that will effectively reduce the volume of driftable fines found in spray droplet spectrums. Many applicators have chosen to use these low-drift designs, mostly as a means to safeguard the applications that are being made from unwanted spray drift. Similarly, many applicators are utilizing drift reduction adjuvants to further lower their risk of drift.
A concern is that many applicators are using these nozzle types and adjuvants without a clear understanding of the correct operating parameters. In addition, a concern has been expressed that this increased emphasis in designing and using nozzles and adjuvants to minimize drift is compromising field efficacy for some pest control and specifically herbicide products. This issue is documented within the application industry by an increased number of performance complaints being registered.
The challenge is to understand what reasons are contributing to failures to control susceptible, hard-to-control and glyphosate-resistant weeds. A related issue is poor performance of glyphosate applications on weeds that are not resistant. While this is a different problem, both lead to the same thing: Uncontrolled weeds in fields.
One of the issues associated with poor performance of glyphosate is poor timing of application in relation to weed size. Ideally, for many weed species, glyphosate is sprayed when the weeds are three to five inches tall. Numerous factors — including wet field conditions, windy days that eliminate the ability to spray and large acreages to cover — all contribute to fields not getting sprayed when weeds are at a stage when they are more susceptible to glyphosate. The larger the weed, the more difficult it becomes to control with glyphosate.
One solution for applying glyphosate to weeds that are larger than the ideal size for spraying is to increase the rate of glyphosate used, which increases the cost of the application. However, even this strategy is failing to provide the proper level of weed control.
Looking For Pest Control
Improved pest control is commonly linked to maximizing coverage on the target. Often the spray parameters needed to improve coverage are the same ones that will result in more drift. Thus, the number one goal of applying a pest control product — maximum efficacy — is often in direct conflict with another high ranking goal, drift minimization.
It has been suggested that in order to have the best opportunity for improved pest control when using drift reducing nozzle technologies, higher than typical spray pressures should be used. With the trend over the last 15 years to encourage applications to be made at lower pressures, it now becomes hard for applicators to believe that using higher pressures will result in lower drift potential when comparing newer and older nozzle technology. Many times, drift reduction strategies are presented to applicators in a manner that seems to encourage both the use of drift reduction nozzles and lower pressures, which only increases the confusion.
In response to the above mentioned industry concerns of reduced pest control while using drift reduction nozzle designs, nozzle manufactures have recently introduced new nozzle types that, while maintaining a drift reduction theme, are providing better coverage and doing so at lower pressures. More information about how and when to use the latest equipment and nozzle technologies to apply crop protection products is paramount for achieving optimum control of undesired pests while minimizing drift.
Associated with the discussion of nozzle technology, the need for better coverage and the ever-present challenge of reducing spray drift, the application industry is moving toward the adaption of prescribing a droplet size for each separate crop protection product that will provide optimum pest control while minimizing spray drift. Future EPA label directives will require applicators to adhere closely to spray droplet standards (ASABE-572.1) during application as a means to improve efficacy while at the same time following a drift reduction technology (DRT) strategy/recommendation to minimize drift into sensitive areas. Perhaps the greatest challenge to recommending specific droplet spectrums for pesticides is the lack of research data using nozzle sizes similar to those used in real world applications.
As a part of this industry standard, nozzle manufacturers are incorporating droplet size information about the nozzles they provide for the application of pest control products in their literature, through the use of on-line nozzle calculators and, soon, with the smart phone apps. Once the label includes specifics on the required droplet size, then applicators will be required to calibrate sprayers to obtain the specified droplet size. This is a phase of calibration that very few are familiar with and will require a major education focus across the industry over the next few years.
Applicators are reminded that making an application that does not totally follow the label directives is “off-label” and could be considered a finable offense by the state agency or not eligible for a “re-spray” from the product manufacturer.
Considering Sprayers
The latest sprayer technology involves the incorporation of various electronic controls designed to improve the efficiency of the application process. GPS technology is allowing for the incorporation of various components including autosteer, automatic boom height control, automatic boom swath control and fieldmapping for prescription/variable-rate applications. There is an increased interest in nozzles designed with flexible orifices to deliver variable-rates to be used to make variable-rate applications. A flow-back control valve designed to reduce spray loss when turning off the spray boom either manually or automatically is now available.
With the majority of spray machines today equipped with electronic controllers, which adjust nozzle flow rate via pressure in response to changes in application speed in order to maintain the targeted GPA, additional concerns are present. With these conventional speed and pressure-based spray systems, as pressure changes to maintain the calibrated spray output rates, a dramatic change in the spray droplet size will occur with each adjustment. The high pressure is needed to increase the flow rate from the nozzle so that the GPA is kept constant.
For example, to double the application speed and maintain the same GPA, a four-fold pressure increase is required. Since these systems are equipped with fixed orifice nozzles, the higher speeds and pressures will result in smaller droplets with high drift potential, while slower speeds will result in lower pressures and larger droplets minimizing drift potential. At the same time, however, pest control efficacy may be sacrificed. Technologies such as pulse width modulation allow for independent control of nozzle flow rate and pressure.
Another challenge related to prescribing and attaining the best droplet spectrum for an application is the impact the pesticides themselves — and any additional adjuvants — have on the droplet spectrum. Recent testing for crop protection product applications have shown that these various products can have a considerable impact on the droplet spectrum compared to spraying only with water.
For both aerial and ground nozzles, the droplet spectrum information available to assist applicators in selecting and setting up their nozzles is based on spraying water or water and NIS. Once the pesticides and other adjuvants are added, the droplet spectrum can be changed, affecting both efficacy and drift.
In situations where products fail to control targeted pests and the application is suspected, it may be the use of a drift reduction adjuvant in combination with a drift reduction nozzle that contributes to the poor results. Research addressing this issue needs to combine both field trials to determine the efficacy of nozzle and adjuvant combinations as well as a measurement of the droplet spectrums for these combinations so that correlations between efficacy and droplet size can be determined. This will help with recommendations in the future when new products enter the market place.
In summary, many factors influence the outcome of the application of pest control products. It is critical that those involved in developing the application strategies have at their disposal the latest and most meaningful information about those factors. This is especially true as more technologies are developed and adapted. Supporting sound research relevant to modern application systems is crucial for that to occur.
The knowledge generated from this research will allow applicators to successfully adopt Application 3.0. It is very critical that all involved in the crop protection industry understand the implications of Application 3.0.
Bob Wolf is manager of Wolf Consulting & Research LLC, Mahomet, IL. He can be reached atbob@rewolfconsulting.com. Scott Bretthauer is an Extension specialist for agricultural and biological engineering at the University of Illinois, Urbana, IL. He can be reached at sbrettha@illinois.edu.
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