This application relates to a method for predicting, and thus reducing, pesticide spray drift resulting from aerial and ground applications onto a target. This method is especially applicable to fixed-wing and rotary-wing applications.
Pesticide drift is principally caused by airborne movement of spray droplets or particles, produced when pesticides in the form of liquid or solid formulations are sprayed over an area of application. Such an operation normally produces a wide range of droplet sizes including very small droplets which may travel in the wind direction over substantial distances, causing off-target deposition of pesticides.
In the United States hundreds of millions of acres receive pesticide application each year. Aerial applications, mainly by fixed wing and rotary wing aircraft are used over much of this area. The extent of the problem caused by pesticide drift may be illustrated by damage claims reported by the insurance industry. For example, between June 1979 and July 1980, claims for crop damages caused by spray drift totaled U.S. $130,000,000, or about 43 cents for every acre that was sprayed. Statistics of this kind do not include environmental damage caused by the uncontrolled spread of pesticides.
When pesticide formulations are aerially applied to an application area, droplets are formed from normal atomization and/or by wind shear during the release of the spray through the air at 50 to 150 mph. The smaller droplets, typically less than 200 microns in initial diameter, may travel over large distances, thus causing off-target deposition of pesticides.
Also, as the droplets, which consist of the active ingredient(s), diluent and carrier, fall toward the target, the evaporation of the carrier, usually water, reduces the size of the droplets. With evaporation the smallest droplets may shrink to a size composed mainly of the active ingredient and a small portion of the diluent. These droplets have a size range of a few microns and may remain airborne. This effect of evaporation of the carrier from the spray formulation, is common to all pesticides applied in the form of solutions.
It is estimated that, due to drift, a significant amount, of the sprayed material never reaches the ground in the intended area of application when applied by an aircraft flying typically at a height of 6-8 feet above the ground and that this loss increases with an increased application height.
Different factors, such as meteorological conditions, spray equipment, type of aircraft, physical properties of the pesticide formulation, operator skill, et cetera, may influence spray drift. Typically, the risk of drift is increased in aerial spraying when high pressure, small,nozzle tips are used in the spraying equipment.
Finally, the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) requires that droplet size distribution tests and field studies be conducted for each pesticide formulation and application hardware. Field studies have been routinely conducted to measure the on-target deposition and off-target spray drift deposition of pesticide formulations resulting from fixed-wing and rotary-wing applications. Spray drift studies cover a limited range of application and atmospheric conditions and additional spray drift studies must be conducted to meet FIFRA requirements for each new pesticide formulation and/or application system. This approach to quantify spray drift deposition is prohibitive because of the cost per study and time required. The cost to conduct spray drift field studies could total in excess of $150,000 for each formulation use pattern.
An alternative approach is to employ a mathematical model, validated from a subset of well designed field studies, for the establishment of standards for proper aerial spraying. These field studies should cover a range of application systems and meteorological conditions. A model would significantly reduce the number of field studies by providing the capability to predict spray deposition for a variety of application conditions given only the spray droplet size distribution and spray cloud dimensions. Hence, a model would assist in product registration efforts (by determination of recommended spray buffer distances). Additionally, a model could also be used during product development to tailor pesticide formulations that improve efficacy and minimize spray drift.