Herbicide Spray Drift
A-657 (Revised), August 1993
Alan G. Dexter, Sugarbeet Specialist
North Dakota State University and the University of Minnesota
Growth regulator herbicides such as 2,4-D or MCPA
may cause leaves of sunflowers to have parallel vein patterns and abnormal leaf shapes.
Herbicide spray drift is the movement of herbicide from the target area to areas where herbicide application was not intended. Herbicide drift generally is caused by movement of spray droplets or herbicide vapors. Herbicide granules or dried particles of herbicides may move from the target area in high winds but are not considered important sources of herbicide drift. While the number of acres damaged and the annual economic loss from spray drift is not large, individuals who are affected can suffer substantial losses.
Herbicide spray drift may injure susceptible crops and could cause prohibited residues in the harvested crops. Spray drift also can damage shelterbelts, garden and ornamental plants, cause water pollution, and damage non-susceptible crops in a vulnerable growth stage (2,4-D drift on wheat in the flowering or seedling stage, for example). Drift also can cause non-uniform application in a field, with possible crop damage and/or poor weed control.
Herbicide drift can occur with any herbicide. However, the risk of damage to non-target plants varies considerably among herbicides and among non-target plants. In general, the risk of damaging drift is directly related to the level of susceptibility of the non-target plant to the herbicide being applied. For example, a non-target plant which would be significantly injured by 5 percent of a normal application rate of a herbicide is more likely to sustain a yield loss from drift as compared to a non-target plant which would be significantly injured by 25 percent of a normal application rate.
Even though only a small portion of the applied herbicide drifts, some non-target areas can receive high doses. Herbicide drift can accumulate on the downwind side of a field, in a shelterbelt at the edge of a field, or in a portion of an adjacent field. In some cases, herbicide accumulated in downwind areas can exceed the rate applied to the field, with a small portion from each pass of the sprayer drifting to the non-target area. Shelterbelts are particularly susceptible to accumulation of high herbicide rates because the trees intercept the drift.
Factors Affecting Spray Drift
Spray particle size
Spray drift can be reduced by increasing droplet size, since a wind will move large droplets less than small droplets (Table 1). Droplet size can be increased by reducing spray pressure, increasing nozzle orifice size, special drift reduction nozzles, additives that increase spray viscosity, and rearward nozzle orientation in aircraft.
Table 1. Influence of droplet size on potential distance
of drift.
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Lateral distance
droplets travel
Droplet Time in falling
diameter Type of required to 10 feet in
(microns) droplet fall 10 feet a 3 mph wind
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5 Fog 66 minutes 3 miles
20 Very fine spray 4.2 minutes 1,100 feet
100 Fine spray 10 seconds 44 feet
240 Medium spray 6 seconds 28 feet
400 Coarse spray 2 seconds 8.5 feet
1,000 Fine rain 1 second 4.7 feet
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Source: Klingman (9), Potts (11) and Akesson and Yates (2)
Research with ground sprayers (5) indicated that addition of a spray thickener increased spray droplet size and reduced spray drift by 66 to 90 percent compared to application without thickener. Research with airplane application (1) indicated that the addition of spray thickener increased the volume mean diameter of spray droplets as compared to applications without thickener. However, the spray thickener also increased the formation of highly driftable small spray droplets less than 122 microns in diameter. The addition of spray thickener should reduce drift from a ground sprayer but may not affect or may even increase drift from aerial application.
Some postemergence herbicides such as fluazifop-P (Fusilade 2000), fenoxaprop (Option II), quizalofop-P (Assure II), phenmedipham or/or desmedipham (Betanex, Betamix), sethoxydim (Poast), bentazon (Basagran) and bromoxynil (Buctril) require small droplets for optimum performance, so techniques which increase droplet size may reduce weed control. Weed control from herbicides which readily translocate such as 2,4-D, MCPA, dicamba (Banvel), clopyralid (Stinger) and picloram (Tordon) is affected little by droplet size within a normal droplet size range, so drift control techniques generally will not reduce weed control with these herbicides. Glyphosate (Roundup) is readily translocated, so droplet size generally has minimal effect on weed control. (Small droplets may be retained better than large droplets on hard to wet grasses). Glyphosate is partially inactivated by increased water volume, so spray volume recommendations on the label should be followed.
Method of application
Liquid formulations of herbicides are applied by airplane, helicopter, ground sprayer or mist blower applications. Low pressure ground sprayers are commonly used for herbicide application and are normally operated at 30 to 50 pounds per square inch with 5 to 20 gallons of water per acre.
Herbicide spray drift generally is greater from mist blower and aerial application than from ground application when application is under similar environmental conditions with all sprayers adjusted properly (6). Low pressure ground sprayers generally produce larger spray droplets which are released from the nozzle closer to the target than with aerial sprayers or mist blowers.
Distance between nozzle and target (boom height)
Less distance between the droplet release point and the target will reduce spray drift. Less distance means less time to travel from nozzle to target and therefore less drift occurs. Small spray droplets have little inertial energy, so a short distance from nozzle to target increases the chance that the small droplets can reach the target. Also, wind velocity often is greater as height above the ground increases, so spray droplets released from a reduced nozzle height are affected by a lower wind velocity (3).
Herbicide volatility
All herbicides can drift as spray droplets, but some herbicides are sufficiently volatile to cause plant injury from drift of vapor (fumes). For example, 2,4-D or MCPA esters may produce damaging vapors, while 2,4-D or MCPA amines are essentially non-volatile and can drift only as droplets or dry particles.
Vapor drift occurs when a volatile herbicide changes from solid or liquid into a gaseous state and moves from the target area. Herbicide vapor may drift farther and over a longer time than spray droplets. However, spray droplets can move over two miles under certain environmental conditions so crop injury a long distance from the intended target is not necessarily due to vapor drift. A wind blowing away from a susceptible crop during application will prevent damage from droplet drift, but a later wind shift could move damaging vapors from the treated field into the susceptible crop. An experiment conducted in Canada demonstrated that 3 to 4 percent of both 2,4-D amine and high volatile ester drifted out of the target area as spray droplets. However an additional 25 to 30 percent of the ester drifted as vapor in the first 30 minutes after spraying while no additional movement of the amine was detected (7).
Relative humidity and temperature
Low relative humidity and/or high temperature will cause more rapid evaporation of spray droplets between the spray nozzle and the target than will high relative humidity and/or low temperature. Evaporation reduces droplet size, which in turn increases the potential drift of spray droplets. For example, very fine particles can drift 367 yards to a few miles with only a 3 miles per hour wind (Table 1). However, low humidity may reduce the phytotoxicity of the herbicide because rapid drying of a spray droplet will reduce herbicide penetration into a plant. Also, plants growing in low humidity produce a thicker cuticle than in high humidity, resulting in greater resistance to herbicide penetration. In general, total drift movement of herbicide out of the target area will be greater with low relative humidity and high temperatures. However, the influence of humidity and temperature on plant injury from herbicide spray drift is not entirely predictable. In some cases plant injury from drift may be increased by low relative humidity and high temperature while in other cases plant injury from drift may be greater with high relative humidity and low temperature.
Temperature also influences the volatility of herbicides. Research results indicate that vapor formation from a high volatile ester of 2,4-D approximately tripled with a temperature increase from 60 to 80 degrees Fahrenheit (8). At 80 F, 2,4-D vapor formation was about 24 times greater from a high volatile than a low volatile ester.
Vapor damage to tomato plants from various formulations of 2,4-D at different temperatures showed vapors from high volatile esters caused injury to plants at all tested temperatures (Table 2). The low volatile esters of 2,4-D did not damage plants at 70 to 75 F but did at 90 and 120 F. Even though low volatile esters of 2,4-D are much less volatile than high volatile esters, vapor drift from low volatile esters can damage susceptible plants. The amine formulation was essentially non-volatile, as no damage-causing vapor was produced even at high temperatures.
These results indicate that a low volatile ester would begin to release damaging vapors at a temperature between 75 and 90 F. However, soil surface temperatures are often much warmer than air temperatures, especially on a sunny day. Thus, vapor drift from low volatile esters may occur at air temperatures lower than 75 F.
Table 2. Relative damage to tomatoes by vapors from 2,4-D formulations held at three temperatures. Ratings taken 24 hours after exposure, with 1=no effect and 6=severe damage. ------------------------------------------------------------------ Temperature and hours of exposure ------------------------------------------ 70-75 F 90 F 120 F 2,4-D formulation 2hr 16hr 2hr 16hr 2hr 16hr ------------------------------------------------------------------ Butyl ester 3.5 6.0 5.8 6.0 6.0 6.0 (high volatile) Butoxyethanol ester 1.0 1.0 2.3 5.7 6.0 6.0 (low volatile) Dimethylamine 1.0 1.0 1.0 1.1 1.2 1.2 (non-volatile) ------------------------------------------------------------------ Source: Baskin and Walker (4)
Wind direction
Herbicides should not be applied when the wind is blowing toward an adjoining susceptible crop or a crop in a vulnerable stage of growth. The wind should be blowing away from the susceptible crop or perhaps the field should not be treated, if weed problems are minor. All feasible drift control techniques should be used if herbicide must be applied while the wind is blowing toward a susceptible crop.
Wind velocity
The amount of herbicide lost from the target area and the distance the herbicide moves will increase as wind velocity increases, so greater wind velocity generally will cause more drift. However, severe crop injury from drift can occur with low wind velocities, especially under conditions that result in vertically stable air.
Air stability
Horizontal air movement (wind) is generally recognized as an important factor affecting drift, but vertical air movement often is overlooked. Normally, air near the soil surface is warmer than higher air. Warm air will rise while cooler air will sink which provides vertical mixing of air. Small spray droplets suspended in the warm air near the soil surface will be carried aloft and away from susceptible plants by the vertical air movement. Vertically stable air (temperature inversion) occurs when air near the soil surface is cooler or similar in temperature to higher air. Small spray droplets can be suspended in stable air, move laterally in a light wind and impact plants two miles or more downwind. Vertically stable air is most common near sunrise and generally is associated with low wind and clear skies. Three times more spray was detected 100 to 200 feet downwind and 10 times more was detected 1,000 to 2,000 feet downwind with vertically stable air as compared to normal conditions with a given wind speed (2).
Spray drift in vertically stable air can be reduced by increasing spray droplet size. Herbicides should not be applied near susceptible crops when vertically stable air conditions are present. Vertically stable air can often be identified by observing smoke bombs or dust from a gravel road. Also, fog is an indication of vertically stable air and dew formation generally indicates vertically stable air.
Spray pressure
Spray pressure influences the size of droplets formed from the spray solution. The spray solution emerges from the nozzle in a sheet, and droplets form at the edge of the sheet. Increased nozzle pressure causes the sheet to be thinner, and this thinner sheet will break into smaller droplets than from a sheet produced at lower pressure. Also, larger orifice nozzles with high delivery rates produce a thicker sheet of spray solution and larger droplets than smaller nozzles.
Nozzle spray angle
Spray angle is the angle formed between the edges of the spray pattern from a single nozzle (Figure 1). Nozzles with wider spray angles will produce a thinner sheet of spray solution, and smaller spray droplets than a nozzle with the same delivery rate but narrower spray angle. However, wide angle nozzles are placed closer to the target for proper overlap than narrow angle nozzles and the benefits of lower nozzle placement offsets the disadvantage of slightly smaller droplets for drift reduction.
Figure 1. Influence of nozzle spray angle on nozzle height
for proper overlap to give uniform spray distribution.
The angle of nozzles relative to direction of travel can influence drift from aerial application. Because of greater wind shearing when nozzles are pointed into the wind, nozzles pointed toward the direction of travel will produce smaller droplets than nozzles pointed back. The smallest droplets are produced from nozzles 45 degrees forward of vertical, while the largest droplets are produced by a straight-back (90 degree) orientation. Droplet size becomes progressively larger as the nozzle is rotated back from 45 degrees forward to the straight-back position.
Nozzle type
Nozzle types vary in droplet sizes produced at various spray pressures and gallons per minute output (Table 3). "Flat fan," "flood" and "hollow cone" nozzles produce similar-size droplets and a similar volume of small droplets when compared at equal spray pressure and equal delivery rate. The flood nozzle tends to produce slightly larger droplets than the flat fan, while the flat fan produces slightly larger droplets than the hollow cone.
Table 3. Influence of nozzle type and spray pressure on droplet size. ----------------------------------------------------------------------- Volume Volume with Delivery Spray Spray median less than Nozzle type rates pressure angle diameter 100 micron dia. ----------------------------------------------------------------------- (gal/min) (lb/sq in) (degrees) (microns) (percent) Flat fan 0.12 15 65 239 (LF-2) 0.17 30 76 194 0.20 40 80 178 17.5 Flood 0.12 15 90 289 (D-1) 0.17 30 115 210 0.20 40 125 185 15.5 Hollow cone 0.12 15 228 (HC-12) 0.17 30 185 0.20 40 70 170 19.0 Whirl Chamber 0.12 15 195 (WRW-2) 0.17 30 158 0.20 40 120 145 23.0 Raindrop 0.11 15 506 (RD-1) 0.16 30 358 0.18 40 90 310 0.8 ----------------------------------------------------------------------- Source: Delavan Manufacturing Company
Two types of Raindrop nozzles have been developed for drift control. The type "RA" is a whirl chamber nozzle with a secondary swirl chamber attached. The type "RD" is a disc-core nozzle with a secondary swirl chamber attached. Compared with the other nozzle types listed in Table 3, the Raindrop nozzles produced the largest droplets and also the lowest volume of small droplet
Spray pressure with ordinary flat fan nozzles should not be less than 20 psi because the spray pattern from the nozzles will not be uniform at lower pressures. The "LP" and "XR" nozzles are designed to give a uniform spray pattern at 10 to 20 psi and this low pressure results in larger spray droplets compared to applications at higher pressures. "Turbo Floodjet" and "Drift Guard" flat fan nozzles also will produce larger spray droplets than ordinary floodjet or flat fan nozzles at a given spray pressure.
Spray shields on ground sprayers
Shields around spray nozzles or spray booms will partially protect spray droplets from wind and reduce spray drift. The small plastic cones which fit around individual nozzles reduce drift by about 25 to 50 percent. Spray shields which enclose the entire boom reduce spray drift by about 50 to 85 percent. Spray shields give a greater percent reduction in spray drift when winds are low and spray droplets are relatively large. Therefore, spray shields should not be used as a substitute for other drift control techniques. Rather, spray shields should be used as a supplement to all other applicable methods of drift reduction.
Air movement around aircraft
"Vortices" are irregular drifts of air around the fixed wing of airplanes or the rotary blades of helicopters. Updrafts are produced by the fixed wind or rotor tip, while downdrafts are produced by the body of the aircraft. The vortices move spray particles aloft with updrafts and down into the target area with downdrafts (Figure 2).
Figure 2. Air currents in wake of high wing monoplane.
Source: Yates and Akesson (15).
A spray boom which covers no more than two-thirds of the distance from the center of the aircraft to the end of the wing or rotor tip will limit the spray released into the updrafts and reduce drift (14). Lowering the spray boom a foot or more below the wing of fixed-wing aircraft or moving the boom as far forward as possible on helicopters also reduces the exposure of spray droplets to vortices.
Proper spacing of nozzles to reduce drift and achieve uniform application varies with the type of airplane. Nozzles generally should be closer together near the end of the boom, with three- to four-foot gaps on the left of center and three or four nozzles grouped to the right of center. Air drawn by the propeller will spread the spray from the clustered nozzles into the area lacking nozzles to form a uniform pattern. Spray distribution should be regularly tested and the nozzle spacing adjusted to produce a uniform spray pattern.
Spray droplets released from a nozzle on an airplane are exposed to the forces of the air passing the nozzle. This creates wind shear and the spray droplets will be broken into smaller droplets. The effect of wind shear can be reduced by orienting the nozzles straight back rather than at an angle to the direction of travel. Solid stream nozzles set straight back will produce the largest droplet size from an airplane
A summary of the influences of various factors on spray drift is given in Table 4.
Table 4. Summary of influences of various factors on spray drift. ----------------------------------------------------------- Factor More drift Less drift ----------------------------------------------------------- Spray particle size smaller larger Release height higher lower Wind speed higher lower Spray pressure hgher lower Nozzle size smaller larger Nozzle orientation forward backward (aircraft) Nozzle location beyond 2/3 wing 2/3 or less wing (aircraft) span span Air temperature higher lower Relative humidity lower higher Nozzle type produce small produce larger droplets droplets Air stability vertically stable vertical mvement air of air Herbicide volatility volatile non-volatile -----------------------------------------------------------
Simulated Herbicide Drift on Sunflower and Sugarbeet
Research has demonstrated that sunflower yield loss from simulated spray drift of 2,4-D and dicamba (Banvel) was influenced by the growth stage of sunflower when the herbicide was applied (13). Sunflower yield loss varied from 25 to 82 percent as compared to an untreated check (Figure 3). Yield loss was greatest when the herbicides were applied in the bud stage and least when applied during flowering. Sunflower with two to four true leaves were affected less than larger pre-flowering sunflower. The growth stage response of sunflower to 2,4-D and dicamba was similar so the results with the two herbicides are combined in Figure 3.
Figure 3. Sunflower yield loss from simulated herbicide drift
applied at various growth stages averaged over 2,4-D at 0.5, 1.0 and 2 oz ai/A and dicamba
(Banvel) at 0.1, 0.5 and 1.0 oz ai/A as compared to an untreated check.
The amount of herbicide which contacted the sunflower and the environment during and following application influenced yield loss caused by simulated herbicide drift (10, 13). For example, 2,4-D at 0.5 ounces active ingredient (ai) per acre applied to 12 to 14-leaf sunflower caused a 5 percent yield loss in one year, but the same treatment caused a 93 percent loss in a similar study conducted in a different year. Equal amounts of drift may cause very different effects on sunflower yield depending on environment. Sunflower injury from herbicide drift will be greatest with warm temperatures and high soil moisture.
Sunflower yield loss from 2,4-D at 0.5, 1.0 and 2.0 ounces ai per acre was 67, 81 and 98 percent, respectively, while dicamba (Banvel) at 0.1, 0.5 and 1.0 ounces ai per acre caused sunflower yield loss of 19, 34 and 58 percent, respectively, as compared to an untreated check when the herbicides were applied to eight-leaf sunflower.
Sunflower height reduction, as compared to undamaged sunflower, caused by 2,4-D, MCPA, or dicamba (Banvel) was significantly correlated with sunflower yield loss (10). Drift of 2,4-D, MCPA, or dicamba which causes a sunflower height reduction also would be expected to reduce yield. However, typical injury symptoms may be observed on sunflower from low amounts of drift without sunflower height reduction. Yield loss would not be expected from spray drift unless height reduction occurs.
Sugarbeet yield loss from simulated 2,4-D drift was influenced by the size of the sugarbeet at application (12). Sugarbeet yield loss generally increased as size of the sugarbeet at application increased (Figure 4). Loss of extractable sucrose per acre was 20 percent when the 2,4-D was applied four weeks after planting and loss increased to 32 percent when the 2,4-D was applied 11 weeks after planting, as compared to an untreated check.
Figure 4. Loss of extractable sucrose in sugarbeets treated
with 2,4-D to simulate drift at various growth stages averaged over two years and rates of
0.5, 2 and 4 oz ai/A as compared to an untreated check.
Early season 2,4-D applications reduced yield in tons per acre but had little effect on percent sucrose while 2,4-D applied late in the growing season reduced percent sucrose but did not reduce tons per acre, as compared to an untreated check (12). Occasionally, late season application of 2,4-D actually increased yield in tons per acre, but the reduction in percent sucrose was large enough to cause a loss in extractable sucrose per acre.
Herbicides are variable in toxicity to sugarbeet both in total amount of herbicide and the percent of labelled amount of product which caused yield loss (Table 5). Pursuit and Harmony Extra at 2 percent of a labelled rate caused 29 and 34 percent loss in extractable sucrose per acre, respectively. Pinnacle caused a 14 percent loss in yield when 6 percent of a labelled rate was applied while Assert caused a 13 percent loss when 13 percent of a labelled rate was applied. In general, the potential for yield reducing drift is greater with herbicides that cause yield loss at lower rates when rates are based on percentage of a labelled rate. Thus the risk of damaging drift would be greater from Harmony Extra, Pinnacle, or Pursuit as compared to Assert, 2,4-D, Buctril, or bentazon.
Table 5. Influence of simulated herbicide drift on sugarbeet yield. ----------------------------------------------- Reduction in extractable Herbicide Rate sucrose/A ----------------------------------------------- oz ai/A % of label % Harmony Extra 0.004 1 4 Harmony Extra 0.008 2 34 Harmony Extra 0.016 4 57 Pinnacle 0.004 6 14 Pinnacle 0.008 13 27 Pinnacle 0.016 26 64 Pursuit 0.016 2 29 Pursuit 0.08 11 72 Pursuit 0.16 21 91 Assert 0.8 13 13 Assert 1.6 26 22 Assert 3.2 53 50 2,4-D 1.0 25 49 Buctril 1.0 25 22 bentazon 3.2 20 8 -----------------------------------------------
Simulated drift of 2,4-D also caused increased loss of extractable sucrose during storage (12). Sugarbeet roots normally lose some sucrose during storage and sugarbeet not treated with 2,4-D lost 20 percent of their extractable sucrose during storage averaged over two experiments (Table 6). However, sugarbeet treated with 2,4-D lost from 27 to 36 percent of their extractable sucrose. Sugarbeet which are damaged by spray drift of a growth regulator herbicide such as 2,4-D should be processed as soon as possible after harvest. Post harvest storage of sugarbeets damaged by spray drift would result in storage of lower quality sugarbeet and in greater sucrose losses in the storage piles.
Sugarbeet may exhibit visible symptoms of herbicide injury from spray drift without yield loss (12). Sugarbeet can recover completely from low levels of damage so the presence of symptoms does not necessarily indicate that a yield loss will result from the drift.
Table 6. Influence of simulated 2,4-D drift on loss of extractable sucrose during sugarbeet storage, averaged over five application dates and two years. --------------------------------------- Extractable sucrose loss during Herbicide Rate storage* --------------------------------------- (oz ai/A) (%) 2,4-D 0.5 27 2,4-D 2.0 34 2,4-D 4.0 36 Untreated check -- 20 --------------------------------------- aStored at 41 F and 95% relative humidity for 150 days in 1978-1979 and 110 days in 1979-1980.
References
- Akesson, N.B., and W.E. Yates, 1984, "Physical Parameters Affecting Aircraft Spray Application." Pesticide Drift Management Symposium Proceedings, South Dakota State University, Brookings.
- Akesson, N.B. and W.E. Yates, 1964. "Problems Relating to Application of Agricultural Chemicals and Resulting Drift Residue." Annual Review of Entomology 9:285-318.
- Anonymous. 1966. "New Pesticide Spray Methods Due This Spring." Chemical and Engineering News 44(13):42-43.
- Baskin, A. David and E.A. Walker. 1953. "The Responses of Tomato Plants to Vapors of 2,4-D and/or 2,4,5-T Formulations at Normal and Higher Temperatures." Weeds 2:280-287.
- Bode, L.E., B.J. Butler and C.E. Goering. 1976. "Spray Drift and Recovery as Affected by Spray Thickener, Nozzle Type, and Nozzle Pressure." Transaction of the ASAE. Vol. 19, No. 2, pp 213-218.
- Frost, K.R. and G.W. Ware. 1970. "Pesticide Drift from Aerial and Ground Application." Agricultural Engineering 51(8):460-464.
- Grover, R., J. Maybank and Y. Yoshida. 1972. "Droplet and Vapor Drift from Butyl Ester and Dimethylamine Salt of 2,4-D." Weed Science 20:320-324.
- Jensen, D.J. and E.D. Schall. 1966. "Determination of Vapor Pressure on Some Phenoxyacetic Herbicide by Gas-Liquid Chromatography." Journal of Agricultural Food and Chemistry 14:123-126.
- Klingman, Glenn. 1961. "Weed Control as a Science." John Wiley and Sons, New York, p. 67.
- Knudson, J.T. 1977. "Simulated 2,4-D Drift on Sunflower and Sugarbeets." M.S. thesis, Dept. of Agronomy, North Dakota State University.
- Potts, S.F. 1946. "Particle Size of Insecticides and Its Relation to Application, Distribution and Deposits." Journal of Economic Entomology 39(6):716-720.
- Schroeder, G.L., D.F. Cole and A.G. Dexter. 1983. "Sugarbeet Response to Simulated Herbicide Drift." Weed Science 31:831-836.
- Schroeder, G.L., A.G.Dexter and Jeff Tichota. 1979. "Herbicide Spray Drift on Sunflower." Proc. North Cent. Weed Control Conf. 34:66.
- Warren, L.E. 1976. "Controlling Drift of Herbicides." Agricultural Aviation. March, April, May and June.
- Yates, W.E. and N.B. Akesson. 1966. "Characteristics of Drift Deposits Resulting from Pesticide Applications with Agricultural Aircraft." Proceedings of the Third International Aviation Congress, Netherlands, March.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the North Dakota State University Extension Service is implied.
A-657 (Revised), August 1993
