Conducting spray operations

Agricultural chemicals applied under unfavorable weather conditions from poorly adjusted or poorly operated equipment can drift away from the target. Crops and pastures can be damaged from the spray drift of herbicides while people, stock and water supplies can be affected by insecticide drift. The resulting pollution, crop damage and the potential health hazards are things that are no longer environmentally acceptable. Additionally, pesticide that drifts away from the target reduces the efficiency of the product on the target and spray failures are a waste of money and effort.

Spray sure

When applying pesticides from their own equipment, farmers should be sure:

the equipment is functioning correctly. Check that nozzles are in good condition, use low pressure and high volume, and keep the boom at the correct height. Use nozzles that produce larger droplets and, if possible, consider raindrop nozzles
pesticides are mixed thoroughly and according to the label
the recommended registered pesticide is used for the job at hand
pesticides are applied at recommended rates
only target plants or weeds are sprayed.

Farmers using the services of commercial operators can rely on the operator for these aspects but it is imperative that they be given full details, preferably with a map, showing:

compass directions
areas to be sprayed
location of susceptible crops, stock, bee hives, houses, sheds, dams
topographical features and hazards
real property locations and description.

Spray safe

Before beginning a spraying activity, operators should be mindful of safety in the pesticide distribution.

Wind conditions

The best condition to spray in, is a light breeze blowing at no more than 10 to 12 km/hr, preferably blowing away from the problem area. Do not spray in strong winds greater than 15 km/hr, or if the wind is in the direction of nearby susceptible crops, homes, buildings, livestock or water supplies. Avoid spraying under still, warm conditions as fine particles can travel considerable distances and it is impossible to predict where they will come down because they will drift in the direction of the next wind.

Wind speed

As a guide to estimating wind speed, the table below is part of the Beaufort scale of wind speeds up to No. 3, when spraying should cease.

Beaufort number	Speed (km/h)	Description	Guide for judging
0	less than 1	Calm	Smoke rises vertically.
1	1 – 5	Light air	Direction of wind shown by smoke drift, but not wind vanes.
2	6 - 11	Slight breeze	Wind felt on face; leaves rustle; ordinary vane moved by wind.
3	12 - 20	Gentle breeze	Leaves and small twigs in constant motion; wind extents light flag.

Beaufort scale of wind speeds

Smoke signals

Use ground smoke signal fires to indicate wind direction and strength and stop spraying if these conditions suddenly change and become unfavorable. Signal fires are a great help to commercial contractors and also serve as an indicator to neighbors. A burning tire makes an ideal smoke signal. The installation of a windsock adds permanency to wind direction indication and strength sensing as long as it is centrally located and highly visible. Smoke needs to be generated for the full spraying period.

Avoid spraying if the smoke rises vertically.

Inversion

Do not spray under inversion conditions. This is where a blanket of cold air is trapped above the ground and temperatures increase with altitude rather than decrease. Blankets of fog or smoke indicate such conditions as smoke will not rise but drift at a constant height under the inversion layer.

Temperature

High temperatures can have a two-fold effect on drift – that of volatilization and evaporation. Firstly, higher ground temperatures establish air currents which result in spray mists being carried high and dispersed over a wide area. Secondly, the high temperatures can evaporate the liquid in the droplets and the particles of pesticide can be carried as a fine mist over long distances. Avoid spraying in temperatures greater than 30oC especially for growth regulator herbicides; eg, dicamba, 2,4-D and MCPA.

Humidity

It is preferable to spray under high humidity. This is particularly important when water is the pesticide carrier as low humidities are often associated with high temperatures and thus, high rates of evaporation. Avoid spraying when relative humidities drop below 45%. Under inversion conditions, do not spray with high humidity as it extends droplet lift and increases herbicide uptake thus increasing drift hazard.

Temperature (^oC)

Humidity (%)

Aerial

Ground

Temperature and humidity levels when spraying should cease.

Spray drift

The movement of spray droplets onto nearby susceptible crops and environs is a grave risk when using pesticides.

Factors contributing to drift are:

weather conditions during and immediately after application
droplet and particle size. This is determined by the application method and equipment used with large nozzles at low pressure reducing drift danger
nature of the spray mixture; that is, its volatility
height and distance. The greater the height and distance from the target plant at which pesticides are discharged the greater is the risk of drift
direction of application. Spraying upwards or into a wind increases the risk of drift.

Safe distances

Safe distances with respect to drift from spraying operations are entirely dependent on weather conditions and application methods. A light wind is highly desirable and essential to carry droplets down into the crop and onto the target. Provided there is a light wind there should be little wind drift and no risk to susceptible crops, homes, stock, sheds and water supplies downwind from the target area. A buffer zone of 300 meters should be adequate for most spraying situations.

However, if the conditions are wrong or equipment is incorrectly set or operated, drift can be substantial and safe distances simply cannot be defined. Under high winds, pesticide can drift several kilometers. Likewise, fine droplets suspended in the air under calm conditions or in hot dry conditions can drift almost anywhere.

Communication

Communicate with neighbors, and commercial operators notifying them of susceptible crops as well as the location of buildings, homes on your property. At the same time, determine the location and nature of these things on neighboring properties.

When spraying, communicate your plans to neighbors who may be affected and discuss any drift risks with them.

Records

In some countries commercial contractors are required by law to keep records of all spraying operations and it is a recommended procedure for all users of agricultural chemicals. Such records can provide good evidence of such operations, should problem arise.

Records should include:

date and time of application
chemical used and rate
crop/pest and area sprayed
weather conditions
equipment and operating conditions.

Map for spraying

To help commercial operators, sketch a map of your farm showing prominent land marks and reference points (see example below). Note susceptible crops both on your farm and on your neighbors’.

A map drawn, preferably with coloring pencils, showing the following, is required.

North
Houses and sheds shown as shaded squares or rectangles.
Number and shape of fields showing whether crop, fallow or pasture
[in green or yellow).
Show field and area to be sprayed.
Show the order in which paddocks are to be sprayed or marked.
Show hill as: (in brown)
Show creeks as: (in blue)
Show dams as: (in blue)
Show roads as: (in black)
Show main contour banks as:
Show trees as: (in green)
Power lines and phone lines to be marked [in red].
Distance and direction from nearest town, main road, river or well known land mark.
Tell the pilot of any susceptible crops, gardens, trees, etc. within 10 km.
Mention any beehive in area and notify the owners.

A detailed map suitable for use by aerial spray operators

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