Reducing pesticide spray drift using a universal computational model

Application of pesticides using air-assisted, ground-based sprayers or airplane sprayers (or even drones in the very near future) has become a necessity to ensure high efficiency crop production. Meanwhile, intensive and extensive pesticide spray also has caused significant safety, health, and environmental concerns. Development of advanced precision and smart spray application technology and management can enable sustainable crop production and reduce the safety, health, and environmental concerns.

 

Off-target deposition and drift of pesticide

Spraying pesticides to suppress plant diseases or insect prevalence is a very complicated process. It involves mechanical generation of spray droplets, delivery of droplets to various plants, interaction of spray droplets with crops and the ambient environment, on-target droplet deposition, off-target droplet deposition onto ground, and off-target droplet drift in the atmospheric environment. Please notice that pesticide is typically sprayed as liquid droplets but sometimes can be applied as very fine dry dust particles. The U.S. EPA defines pesticide spray drift as “the movement of pesticide dust or droplets through the air to any site other than the area intended.” Obviously, we all wish a 100% on-target pesticide deposition because both off-target ground deposition and atmospheric drift represent not only as a loss of chemicals and waste of money, but also serious environmental pollution problems. In reality, the off-target spray droplet deposition and drift vary widely as a few types of traditional pesticide sprayers are widely used with relatively constant settings for different crop production at different geographic regions with highly varied environmental conditions. The off-target spray droplet deposition and drift can account for a large percentage of the total pesticide applied. Up to 70 million pounds of pesticide active ingredients are wasted to drift per year. Between 1% and 10% of agricultural pesticide sprays drift from the target.

 

Environmental and health concerns

When spraying pesticide, chemicals drift and transport through nearby fields and reach long distances in both rural and urban areas, it can have direct impact on humans, animals, and the environment. On non-target areas, pesticides can damage nearby vegetation and impact nearby aquatic systems. Drift of herbicides can injure other non-target crops. Exposure of humans to pesticides can potentially result in both acute problems such as skin irritation and asthma and chronic pulmonary diseases such as cancer.

 

Key factors affecting pesticide application

Pesticide off-target deposition and drift are primarily affected by the weather conditions and application operating conditions. The weather conditions include wind direction and speed, ambient air temperature, relative humidity, and the terrain and vegetation. The pesticide application conditions include the type of nozzles used, nozzle operating pressure, nozzle size, boom height, spray volume, droplet or particle size, and spray control.

 

Development of advanced intelligent sprayers

To reduce the off-target pesticide deposition and drift, researchers at the USDA-ARS Application Technology Research Unit (ATRU) have been conducting research for 75 years and made significant scientific and technical contributions for optimizing pesticide application technologies to improve pesticide application efficiencies, protect crops from pest damages, and safeguard environmental quality and food and worker safety. Recently, Heping Zhu, an Agricultural Engineer and the Lead Scientist at ATRU has led the development of sensor-guided intelligent sprayers for efficient variable-rate pesticide applications and a significant reduction of off-target pesticide deposition and drift.

Assessment and control of pesticide drift using mathematic models. To further control the off-target pesticide deposition and drift, mathematic computational models can be developed to simulate interactions of pesticide droplets with corps to predict drift potentials in coordination with local weather conditions. Over the years, different models have been developed for prediction of drift from pesticide spray application. The models are expected to account for the pesticide movement including the effect of gravitational acceleration, air resistance, evaporation, and mode of application, and be used more universally. However, due to the complexity and high variability of the pesticide drift issues, there is no simple method existing for effective assessment of the issue. It is very difficult to control the drift without proper assessment methods. An effective, but simple assessment method and integration of the assessment with spray equipment control is needed.

Researchers, Sewoon Hong, a postdoctoral research associate and Lingying Zhao, an extension engineer and professor, at The Air Quality and Bio-Environmental Engineering Lab (AQBEL) of The Ohio State University, are collaborating with Heping Zhu to develop the much-needed model tools as an effective approach to control pesticide application schedules for further minimizing drift potentials for the intelligent sprayers. We are applying recent advances in dispersion models to develop and validate a universal pesticide dispersion model and a model based expert system that will enable environmentally friendly and effective pesticide applications.

A universal spray drift model based on Computational Fluid Dynamics (CFD) is being developed using FLUENT to calculate complicated flow and dispersion close to the equipment and to distances up to 200 m. Then the outputs of the universal models will be used as inputs for the long-range dispersion and transport (0.2-10 km) using the U.S. EPA air pollution dispersion models: AERMOD and CALPUFF. These models will be validated by actual observations of spray drift from field studies. The values of spray drift distance and off-target deposition from validated models as a function of the weather conditions, topography, and terrain conditions will be interpolated, and then a database will be created. A user-friendly interface will be developed to access the database under-specified conditions, and this will be fed into the instrumentation of the sprayer equipment to help make intelligent spray decisions. The model tools will provide a practical approach to assess the probable risks of pesticide spray and help explore application strategies to mitigate pesticide drift, pesticide waste, and environmental and health risks.

In summary, application of pesticides has become a necessity to ensure sustainable, high efficiency crop productions. Off-target pesticide deposition and drift have caused significant safety, health, and environmental concerns. Researchers at the USDA-ARS Application Technology Research Unit (ATRU), led by Heping Zhu, has developed sensor-guided intelligent sprayers for efficient variable-rate pesticide applications and a significant reduction of off-target pesticide deposition and drift. Researchers with OSU and ATRU are collaborating to develop a universal spray drift model to further control operation schedule of sprayers to reduce the off-target deposition and drift of pesticide.

Lingying Zhao, Professor and Extension Ag. Engineer, can be reached at zhao.119@osu.edu. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research & Development Center, and the College of Food, Agricultural and Environmental Sciences.

 

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