The do’s and don’ts of aerial application

By dr. Gerhard Verdoorn
Afrikaans version published in SA Graan
April 2020

Agricultural crops face constant competition from plant pests, diseases and weeds that challenge their health and erode the farmer’s profitability if these undesired elements are not managed properly and timeously. Pesticides or agricultural remedies are available for the effective management of virtually all pests, diseases and weeds in South Africa, and it is the farmer’s prerogative to choose the correct, registered remedies to manage the crop for optimum production and profitability. The majority of pesticides that are registered in South Africa are listed on Agri-Intel with user friendly dropdown menus that make life easy while searching for suitable remedies. It is critically important for the farmer to avail him or herself of the pesticide facts by drawing the labels from Agri-Intel and studying the directions for effective and responsible use. This will guide the farmer in the application technology that may be used for a pesticide, meaning whether it is only for terrestrial application like tractor boom spray or mist blower, or is it also registered for aerial application? Aerial application is sometimes the preferred method of dispensing the pesticide due to crop structure, growth stage or environmental conditions like flooding that make terrestrial application undesirable or impractical.

Aerial application of pesticides is governed by three sets of regulatory frameworks, namely the Fertilizers, Farm Feeds, Agricultural Remedies and Stock Remedies Act, 1947 (Act No. 36 of 1947), the Civil Aviation Act, 2009 (Act No. 13 of 2009) and the SA National Standard for Aerial Application of Pesticides SANS10118 plus the supporting regulations of the two acts. Aerial application of pesticides is much more onerous that terrestrial application due to the increased risk of this method of application and the skills required to do such application.

A pesticide must be registered for aerial application
This act regulates the registration, manufacture, disposal, sales and use of pesticides (agricultural remedies). A pesticide must be registered for aerial application to be used as such and the label of such a pesticide shall have certain clauses from SANS10118 printed on the label and specific instructions for aerial application under directions for use. If a label does not have this information, the pesticide may not be applied by aerial application. One of the biggest problems we face with aerial application is tank mixes; it is not uncommon for an aircraft to take off with a mixture of up to seven pesticides in the tank. Forget about the legal ramifications of such irresponsible practices; just consider the compatibility of all the pesticides in one tank. Some pesticides are simply incompatible due to different pH requirements or chemical reactions that may render them inactive. Another problem arising from such tank mixtures is that it doesn’t have enough water to deposit the active ingredients effectively onto the target and results in poor product performance, undesired synergism or antagonism. The simple rule is to follow label instructions and not deviate from it.

  • Check on the label whether a pesticide is registered for aerial application.
  • Insist that the crop adviser recommends and supplies a pesticide that is registered for the crop, the pest, weed or disease and for aerial application.
  • Apply a pesticide by aerial application if it is not registered as such.
  • Do not take advice about making unregistered tank mixtures.

Minimum spray volume for aerial application
Aircraft (fixed wing, helicopters, micro-lights and drones) cannot carry the same volume of spray mixture as a typical terrestrial spray tank, hence the spray volume dispensed per hectare is much lower than for terrestrial application. Labels of pesticides that are registered for aerial application generally indicate a minimum spray volume of 30 to 40 litres per hectare; it is advisable to use larger volumes if possible because the larger the spray volume, the better the deposition of the pesticide onto the target. The minimum spray volume may be totally ineffective in some cases such as for the infamous Fall armyworm (FAW) in fully grown maize: using only 30 litres spray mixture per hectare of an insecticide is not enough to deposit the active ingredient in the plant whorl where the fifth and sixth instar larvae live and damage the plant. It is therefore ill advised to use aerial application for this particular pest in its advanced developmental stages in maize. For normal pests and diseases, aerial application even at the low dispensing spray mixture volume may be advantageous because the aircraft’s motion assists effective depositing of the spray mixture onto the target.

  • Apply at least 30 litres spray mixture per hectare.
  • Apply less than 30 litres spray mixture per hectare.
  • Apply by aerial application for pests hiding in the whorl or inside cobs or ears.

Certain weather conditions to monitor and avoid for aerial application
Weather conditions play a critically important role in the safe and effective application of pesticides irrespective of whether it is terrestrial or aerial application. The general rule of thumb is to spray when wind velocity is between 5 and 15 kph while for any glyphosate application spraying must terminate when wind velocity exceeds 10 kph to prevent vegetation damage (this is also stated on glyphosate labels). This rule applies to both terrestrial and aerial application. One may question the need for some wind and the rationale is quite simple: the air movement assists with depositing the spray mixture into the target. A totally windless day spells risk because the spray mixture may be suspended in the air and drift off the target area with potentially dire consequences for other crops, natural areas and human health. Windless days be a result of temperature inversion where cool air on the surface is physically blocked from moving upwards by a pocket of warm air overlying it. It is easy to spot temperature inversion: smoke pours out of a chimney only up to a certain height and then drifts sideways. Temperature inversion can result in significant off-target drift and must be avoided at all costs; such conditions normally prevail in the early morning. Wind velocity over 15 kph must be avoided because it increases the potential for serious drift onto non-target areas.

High ambient temperature is also a problem for both terrestrial and aerial application because it results in evaporation of the water from spray droplets, reduction in droplet size and poor deposit onto the target. One can well imagine that such small droplets will be much more prone to drift than the recommended size of droplets. Avoid situations where rain may be falling shortly after spraying because the product may not be rain fast. Some labels will indicate the time required for the pesticide to become rain fast; if no such indication is offered check the local weather forecast and work towards a “dry” period of six hours after application. Lastly, avoid spraying when the crop is covered in heavy dew. Rather wait until the dew has damped off before spraying.

  • Choose weather conditions with a mild wind and ambient temperature of less than 30 degrees Celsius.
  • Spray when there is a temperature inversion.
  • Spray in total windless conditions.
  • Spray when the wind velocity exceeds 15 kph, and 10 kph for glyphosate applications.
  • Spray when ambient temperature rises above 30 degrees Celsius.
  • Spray when rain is imminent.
  • Spray when crop is wet with dew.

Label specific restrictions for some aerial applications
The Registrar of Act No. 36 of 1947 may impose certain conditions on any registered pesticide. One such condition which is applicable to aerial application is that 2,4-D esters may not be applied by aerial applications in some parts of the country like KwaZulu-Natal and the Western Cape due to drift and potential crop and environmental damage. It is therefore necessary to study the label and check for any restrictions that apply to the product before choosing it for aerial application on the farm.

  • Check the label for any restrictions in terms of aerial application.
  • Apply the pesticide by aerial application contrary to the restriction.

A pilot of an aircraft used for aerial application must be registered as an aerial application pest control operator by the Registrar of Act No. 36 of 1947 to offer services as an aerial applicator. These requirements are subject to other requirements of the Civil Aviation Act and its regulations bit that will be discussed further on in the article. The PCO regulations have certain requirements that are in conflict with those of the SANS10118 but the basics are as follows:

The farmer must identify any sensitive areas such as adjacent crops, natural areas, wetlands, human habitation, community centres and places of animal husbandry such as feedlots, poultry farms and dairies. This information must be made available to the pilot prior to commencing with the spray operation so that those areas can be avoided. When such areas are in close proximity to the application area, a buffer zone must be maintained to prevent spray deposit onto such areas. The farmer must also advise immediate neighbours of pending aerial application operations either telephonically or in writing. Some of the pesticides have a strong and unpleasant odour and even if the concentration of such pesticides in the atmosphere is of no or very low risk to people, it may trigger a profound response from people. Farmers must warn neighbours when such pesticides will be applied and strongly suggest that neighbours vacate their premises while the spraying is done. Notification to members hardly ever happens and leads to lots of negative interactions with neighbours. Billboards around the target area are also required according to the regulations to warn about the aerial application of pesticides. The target area must be clearly marked out by the farmer for the sake of the pilot and this mostly done by providing GPS coordinates to the pilot.

The pilot must record the spray operation in his spray log and provide the farmer with a record of what was sprayed. A new rule in the revised SANS10118 that should be promulgated sometime during 2020 is that the aerial applicator (pilot), farmer and agent share the responsibility for the application. This means that on the day of the aerial application the pilot, farmer and agrochemical agent must all agree on the pesticide that should be applied, the dosage and the buffer zone required for the operation. A buffer zone is a safety zone between the area of application and sensitive areas. to prevent undue exposure of people, farming operations and the natural environment to the pesticide.

  • Only use the services of a pilot that is registered as an aerial application PCO.
  • Inform neighbours about the aerial application.
  • Mark the target area clearly for the pilot.
  • Identify sensitive areas and inform the pilot about it.
  • Demarcate and implement a buffer zone.
  • Spray when there is a temperature inversion.
  • Spray in total windless conditions.
  • Spray before dew has dampened off the crop.
  • Don’t spray close to sensitive areas.


The CAA has a set of regulations for aircraft and pilots that operate aircraft for aerial application of pesticides. It covers all aircraft including drones that are defined as remotely piloted aircraft (RPA). There is no difference between the regulations for piloted aircraft (helicopters, fixed winged and micro-light aircraft) and RPA. They must all be licensed and certified for aerial application of pesticides (sometimes called “crop dusting”). Pilots of piloted aircraft and operators of RPA must be licensed as commercial pilots with an agricultural rating for aerial application before they may apply for the aerial application pest control operator registration under Act No. 36 of 1947. Pilots must also have the competency to operate the radio telecommunications required for commercial pilots and be in possession of the necessary radio telecommunication equipment. It is not simply a case of buying a drone and offering aerial application; the person must be fully qualified and certified just like a commercial pilot who flies an aircraft.

It is the farmer’s responsibility to check the certification of a pilot of any type of aircraft and also his or her aerial applicator’s registration under Act No. 36 of 1947. Also check and make sure the aircraft (including drone) is licensed and certified for crop spraying. Failure to do so may land you with an unlawful operator and probable contravention of both Act No. 36 of 1947 and the CAA.

Air safety is of paramount importance when doing aerial application of pesticides. It is a good principle for the pilot to log into the closest air traffic control tower and log his or her operation; take note that this holds true for drone operators also. It is very important for licensed drone operators to make sure they are tuned into the local air traffic radio frequency and alert all pilots of other aircraft of their operations. Failure to do so may end up in a collision between a drone and an aeroplane or helicopter and the results are disastrous.

  • Make sure the aircraft and pilot are both licensed and certified for aerial application by the Civil Avian Authority.
  • Pilot must have radio communication with other aircraft and report to air traffic control.
  • Use the services of unlicensed and uncertified pilots and aircraft, especially not unlicensed drone operators.
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