Reducing Pesticide Drift And Crop Damage

Agdex#:	607
Publication Date:	10/88
Order#:	88-118
Last Reviewed:	08/09
History:	Replaces Factsheet "Pesticide Drift", January 1976
Written by:	R. Frank - Agricultural Laboratory Services Branch/OMAF

Table of Contents

1. Introduction
2. What is Drift?
3. Concerns about Drift
4. Factors Affecting Drift
5. Equipment and Techniques to Reduce Drift
6. Pesticides Used
7. Weather
8. Sprayer Operation
9. Pesticide Application by Airplane or Helicopter
10. Legislation
11. Warning
12. Acknowledgement

Introduction

Pesticides are required for controlling pests that injure or damage agricultural crops. Unfortunately, the efficiency of many application systems and techniques leave room for improvement. Frequently a portion of the spray fails to reach the target pest or area, and deposits on adjacent properties where it can cause damage to animals (including humans) and/or plants. This movement of pesticide to non-target areas is called drift.

What Is Drift?

Drift is the airborne movement and deposition of particles or droplets outside the target area. There are two types of drift;

Spray Drift

This is the aerial movement of pesticide droplets after release over the area being treated. It is facilitated primarily by wind, and air-currents. Large or coarse droplets normally move laterally only, short distances fall in or close to the target. On the other hand, small particles can remain suspended on air-currents for long periods and be carried and deposited at varying distances from the point of discharge and out of the target area.

Most spray nozzles produce a wide range of droplet sizes. The larger droplets strike the target or fall to the ground in the target area. As the droplet size declines a critical size is reached where they readily move laterally on air-currents away from the target area. When the spray droplet size falls below approximately 100 microns (1/250 inch), descent is very slow. Droplets of smaller size can remain suspended in the air for long periods and drift long distances. Drift is not limited to liquid applications; lightweight dusts are also very susceptible to drift.

Vapor Drift

This is the movement of vapors generated as a result of volatilization or evaporation of the pesticide and subsequent movement by wind to non-target areas. Evaporation may occur from droplets at the time of application or following deposition on plant or soil surfaces following application. Volatilization can and often occurs after the spray has dried. Volatile pesticides (e.g., ester formulations) are more susceptible to vapor drift. Volatile pesticides are usually not recommended or sold in areas where the risk to susceptible crops can be a problem.

Concerns About Drift

When pesticides are released from spray equipment, it is intended that the droplets land on the target. This can be accomplished by the proper choice of nozzles, pump pressures, application equipment and the type of pesticide. Spray can drift outside the target area during application, or vapor drift can subsequently move off the target area especially under hot conditions. Either drift can damage crops, animals, or humans and can endanger pollinating insects. The following problems can be created by allowing drift to deposit outside the target area:

Adjacent Crop Damage

When spraying crops, fence rows, or rights-of-way, spray drift can damage adjacent susceptible crops. It is important to be aware of the location of neighbor's susceptible crops when applying herbicides to your crops. In the past damage has occurred frequently when using 2,4-D type herbicides, although it can also happen with other herbicides like atrazine. Herbicides used to control broad-leaf weeds like 2,4-D, MCPA, 2,4DB etc. can damage susceptible crops like tomatoes, soybeans and grapes. In addition, deposits of drifting any pesticide can contaminate adjacent crops that are close to harvest, and leave unacceptable residues on the marketable produce or they can create a hazard to people and livestock consuming contaminated food or feed. As an example, the use of diquat as a top-killer can result in deposits from spray drift leaving adjacent crops with unacceptable residues.

Water Contamination

Spray drift can be deposited in ponds, streams or other water bodies, and (i) be toxic to fish, wildlife, domestic animals or humans, (ii) impart an off flavor to drinking water; or (iii) render water harmful to crops if used for irrigation.

Effectiveness of Pesticide Application

Drift to non-target areas reduces the amount of pesticide deposited in the target area and if the loss is excessive may result in the treatment being ineffective.

Factors Affecting Drift

The factors causing drift can be complex involving environmental conditions and spray practices. The environmental conditions of greatest importance are wind direction and velocity, air-turbulence, relative humidity, barometric pressure, and air-temperature.

The most important spray practices involve the size of spray nozzles, the height of spray release above the target or canopy and the spray pressure. Once released spray droplets do not remain of constant size but decrease in size through evaporation and/or volatilization. The major factors affecting drift are:

Wind Velocity

Air-movement will result in some of the spray droplets being carried off the target area. The amount of spray drift leaving the target increases significantly with increasing wind speeds. Above 10-12 km/hr spraying should be terminated because spray drift can become uncontrollable and unacceptable.

Droplet Size

Coarse droplets deposit rapidly, fine droplets deposit slowly, and hence as the size of spray droplet becomes smaller, spray drift of the target normally increases. The droplet size can be altered by the choice of larger sized spray nozzles and lower pressures. Small nozzles and high pressures produce finer droplets and increase spray drift.

Temperature And Relative Humidity

Warming temperatures and decreasing relative humidity increase the rate of evaporation of the spray droplets as they fall on the target and thereby increase the risk of both spray drift and/or vapor drift. On hot days the land warms up giving rise to upward convection currents that can carry droplets above the crop canopy during spraying, and lateral air-movements can transport these particles away from the target area.

Distance Between Nozzle And Target Area

As the boom or release height above the target or crop canopy increases, the potential for spray drift also increases.

Equipment And Techniques To Reduce Drift

There are several ways to minimize the potential for spray drift and these involve adjustments to the equipment and others relate to the techniques of application.

Equipment

Some types of equipment are available which will minimize the amount of spray drift during applications. In general, equipment which produces spray of large droplet size will have a lower potential for creating problems of spray drift. Droplet sizes can most easily be increased by altering the sizes and types of nozzle. Equipment can be chosen and adjusted to produce a minimum of fine droplets. Wiper applicators which do not create any spray may be of use in situations where the treated crop or lands are close to susceptible crops. In general there are four broad categories of equipment for ground application of pesticides.

1. Air-blast sprayers. This is a vehicle-mounted or vehicle drawn application device utilizing an independent mechanically produced stream of air to assist the transport of the pesticide beyond the orifice of the device. Because this type of equipment uses an air stream to carry the pesticide the potential for drift is always high. Procedures for the major use of air blast sprayers, namely in the orchard sprayers, is addressed in the Ontario Ministry of Agriculture and Food Publication 373 Orchard Sprayer. This publication describes the general principles in their operation and maintenance.
2. Boom type sprayers. This includes a wide variety of equipment and achieves distribution of pesticide through a series of nozzles attached to a boom that extends out on either side. The height of the boom can be adjusted and the type of size of nozzles can be changed. By these means drift can be controlled and minimized.
3. Boomless type sprayers. This type of equipment can consist of a cluster nozzles or spinning discs which give the required spray pattern without the need for a boom. Often the cluster nozzles create large-sized droplets which can reduce spray drift. However, the spinning disc can also produce very small droplets and create a drift problem.
4. Wiper/wick systems. These systems make mechanical contact between crop and pesticide and deposit pesticide by wiping of the stems and leaves in the target area. Because there are no spray droplets involved with this method, spray drift is not a problem.

Techniques

There are many ways in which drift can be minimized when using the above types of equipment. However, there are a few considerations which should always be followed:

1. The use of types of nozzles that produce the largest droplet sizes while at the same time giving good coverage of the target area are recommended. Charts are available that show how the nozzle type affects the volume output and the range of droplet sizes. For roadside spraying the use of controlled droplet spray nozzles, such as Directa Spra or Radiarc, produces a uniform spray droplet thus minimizing the creation of fine spray particles and hence providing a high degree of drift control.
2. Reducing the distance between the nozzle and the target when spraying is helpful. One should make sure of checking the coverage as this can be reduced as the boom is moved too close to the target. Always recalibrate the sprayer if and when the boom height is altered. The fact that newer equipment has bigger tanks and booms that are wider and 'self levelling' may not work well by lowering the boom, since this can accentuate errors of overlapping or missed areas. Therefore, this modification should be approached with care and the sprayer should not be operated out of the recommended range supplied by the manufacturers of the nozzles.
3. Operators should keep nozzles and equipment free flowing at all times and should check nozzles frequently for wear and blockage. Nozzles should be cleaned or replaced when required. Calibrating each nozzle will help to determine when excessive wearing has occurred.
4. Spray operators should not use high-pressures when making herbicide applications. High pressure creates small droplet sizes thereby increasing the potential for drift.
5. Applicators can use an approved drift reducing compound to reduce drift. Such compounds make droplets fall faster by increasing the viscosity or density of the spray and thereby creating a lower potential for spray drift. The use of various additives (Bivert HP, Norbak 60B, Nalco-Thol etc.), now available for treating lawns, roadsides and rights-of-way, will reduce spray drift (see OMAF Publication 75 Guide to Weed Control). Follow the label instructions on the spray additives and also observe normal precautions.
6. With air-blast sprayers, spray drift can be reduced by spraying back into the orchard from the line fence when spraying the outside two to four rows of trees.

Pesticides Used

The major procedure to reduce vapor drift and help in reducing spray drift involve the selection of the pesticide product and its formulation. Before selecting the pest control product for use become familiar with the toxicity, volatility and the way in which the product is formulated. This can help in determining its potential to drift. The same pesticide may be available in other formulations less volatile than others. For example granular formulations rarely drift while emulsifiable formulations are more likely to drift. Amine formulations usually are less prone to vapor drift than ester formulations (e.g. 2,4-D esters are more volatile than 2,4-D amines). This is characteristic of many herbicides. In choosing a formulation select the less volatile material and formulations for use near susceptible crops. This will decrease spray drift and vapor drift but not eliminate it.

Herbicide Spraying

In the application of herbicides, especially of 2,4-D type weed killers often called hormone type or chlorophenoxy and chlorobenzoic acids (for example 2,4-D, mecoprop, dichlorprop, dicamba, etc.), sensitive crops (grapes, tomatoes, turnips, tobacco, beans, carrots, beets, fruit trees, ornamental plants and many others) adjacent to the target area can be damaged by vapor drift or spray drift. To reduce the danger of herbicidal drift:

1. Use only amine formulations when it is necessary to apply the 2,4-D type herbicides (2,4-D, mecoprop, dichlorprop, etc.) near sensitive crops.
2. Very slight spray drift with herbicides containing dicamba can result in damage to many crops and especially soybeans. Under high temperatures (in excess of 25⁰C) dicamba vapor can move from treated plant foliage to susceptible crops within one to two days of application. Thus, the use of dicamba-containing herbicides especially on rights-of-way should be avoided near sensitive crops.
3. Crop damage potential because of both spray drift and vapor drift:
   

   i) Extreme - picloram (Tordon)
   ii) Very high - dicamba (Killex, Kilmore, Banvel etc.)
   iii) High - 2,4-D, MCPA, dichlorprop, 2,4DB, MCPB,

   Crop damage potential because of spray drift:

   iv) Very high - diquat (Reglone), paraquat (Gamoxone)
   v) Medium to high - all herbicides, most commonly atrazine

Weather

It is best to spray pesticides when there is no wind or when the velocity is low. Increasing wind speeds give a higher potential for spray and/or vapor drift to non-target plants. If wind velocity exceeds 10-12 km/hr suspend operation until the wind speed drops. The use of canopies and spray equipment can reduce or minimize drift. Early morning and late evening are often the best times to be conducting spray operations; at these times air is often stationary or only slight moving.

In order to minimize the potential for vapor drift do not spray when the air temperature is very high (excess 30⁰C) or predicted to become high within hours and when the relative humidity is low. Consult the pesticide label and adhere to any directions regarding maximum temperatures for application.

Sprayer Operation

Pesticide applicators should make every effort to prevent or minimize pesticide spray drift by paying attention to:

1. correct calibration and maintenance of equipment
2. correct operation of equipment
3. the volatility and toxicity of the pesticide and
4. weather conditions

To reduce drift:

1. Use flat fan nozzles only
2. Use 110º nozzles, 45-50 cm above the target on 50 cm spacings
3. Use nozzles that have a wide pressure operating range (20-60 psi) and use only at the lowest operating pressure in order to generate large droplets.
4. Do not spray with volumes less than 150 1/ha.

Whenever changes are made to nozzles, pump pressure, vehicle speed or swath width, make sure you recalibrate the sprayer.

Pesticide Application By Airplane Or Helicopter

Aerial applicators of pesticides must be licensed by the Ontario Ministry of the Environment. In addition, permits are required from the Ontario Ministry of the Environment under the authority of the Pesticides Act for the application of Schedule 1 and 5 pesticides and Schedule 2 hormone-type herbicides. The area to be treated will be inspected by Ministry personnel to ensure safety of application.

It is an offence under the Federal Pest-Control Products Act to use a control product under unsafe conditions. Precautionary practices must he heeded at all times to prevent drift. Extra precautions should be taken when using insecticides applied by air, especially those known to be toxic to honey bees, e.g. Sevin (carbaryl), Furadan (carbofuran).

Aerial applicators of pesticides should be familiar with and aware of weather conditions and inversions which could lead to pesticide spray movement off the target area. Evenings and early mornings are the preferred times for spraying as air is usually stationary.

Legislation

It is important to be aware that anyone using pesticides is responsible for their safe application. Should there by any impairment of the quality of life or environment in the use of a pesticide, charges could be laid against the applicator under Section 3 of the Pesticide Act. Section 3 is reproduced here in its entirety to illustrate how all encompassing this legislation is with regards to a violator.

Section 3. No person, whether acting or not acting under the authority of a license or permit under this Act or an exemption under the regulations, shall deposit, add, emit or discharge or cause or permit the deposit, addition, emission or discharge of a pesticide or of any substance or thing containing a pesticide into the environment that,

1. causes or is likely to cause impairment of the quality of the environment for any use that can be made of it greater than the impairment, if any, for such use that would necessarily result from the proper use of the pesticides;
2. causes or is likely to cause injury or damage to property or to plant or animal life greater than the injury or damage, if any, that would necessarily result from the proper use of the pesticide;
3. causes or is likely to cause harm or material discomfort to any person greater than the harm or material discomfort, if any, that would necessarily result from the proper use of the pesticide;
4. adversely affects or is likely to affect adversely the health of any person to a greater degree than the adverse effect, if any, that would necessarily result from the proper use of the pesticide;
5. impairs or is likely to impair the safety of any person to a greater degree than the impairment, if any, of the safety of any person that would necessarily result from the proper use of the pesticide; or
6. renders or is likely to render, directly or indirectly, any property or plant or animal life unfit for use by man to a degree greater than the unfitness, if any, that would necessarily result from the proper use of the pesticide. 1973, c. 25, s.3

Warning

The methods and materials given in this Factsheet can reduce, but do not eliminate pesticidal drift. In areas near sensitive crops, all normal precautions must be taken. It should be emphasized that extremely low, even invisible, amounts of spray drift can be very damaging to sensitive crops. In some cases, spraying during the growing season should not be considered. Drift of fungicides and insecticides while not damaging the crop can leave unacceptable residue of human or animal consumption.

Acknowledgment

Thanks are extended to Brian Allen, Ontario Hydro; Max Morse, CIBA-Geigy; Ralph Dell, Ontario Ministry of Transportation and Communication; John Onderdonk, Ontario Ministry of Environment; Dr. Gerry Stephenson, Environmental Biology and Douglas McLaren, Ontario Ministry of Agriculture and Food for helping with this Factsheet.