Different methods are used for the application of Herbicides, Fungicides & Insecticides. One must determine the target, for example broad leaf weeds or grasses have very different characteristics to an insect, and a fungus is different again. Do you need to add a wetter some oil or both? First of all read and follow the directions suggested on the product label. A great deal of research at considerable cost has been made by the product manufacturers, to apply any product outside the recommended guidelines is a recipe for failure and the manufacturer will not be liable should such a failure happen.
Dunn Aviation use two main types of application equipment to apply liquid products, Micronairs and CP nozzles. Micronairs can be set for a droplet spectrum anywhere between 20 and 150 micron. For an idea of the size of spray an aerosol can, such as fly spray, sprays a liquid at about 20 micron. Rarely would we use such a fine droplet as it is extremely difficult to control the spray drift, also in warm conditions the product may never reach the target before evaporation. To help control drift, particularly when applying herbicides, we prefer to use the CP nozzles as they produce a larger droplet and are therefore less prone to drift away from the target. A CP nozzle can produce a droplet between 50 and 300 micron. Although it may seem there is little difference in droplet size between the micronair and the CP nozzle the spraying characteristics of the two are quite different. Application volumes vary depending on client or job requirements from 100 litres per hectare right down to as little as 2 to 3 hundered millilitres per hectare.
The micronair has a cage that spins at high speed by having its own small propeller blades attached, this speed can be varied by changing the angle of the blades. The product in liquid form is pumped into the spinning cage and is literally smashed up to create the small droplets. The liquid then leaves the micronair in its droplet form at high speed in a spinning or circular motion. This circular motion allows the product to move in and around the target coating all sides of the object intended. The CP nozzle on the other hand forces the product under pressure onto a small deflector plate which spreads the liquid in an even and somewhat more directed state. Both these applicators coupled with the high speed of the aircraft moving across the crop produce an extremely consistent spray pattern over the whole of the crop.
The size of a spray droplet determines where that droplet will land on a plant. Also it needs to be considered that most fungicides are translaminar and translocatable, ie they move through the plant and while moving through the plant they are subject to some dilution. Therefore, a densely foliaged crop requires more chemical than a lighter foliaged crop. For example, selecting a 75 micron droplet size and applying one litre per hectare of Triadimethon it can be concluded that 660 mls of chemical will be collected on the vertical parts of the plant (flag leaf, foliage etc) whereas the other 340 mls will be dispersed onto the horizontal surfaces (the ground, other parts of the plant, broadleaf weeds etc) If a 300 micron droplet is selected then 110 mls is collected on the vertical parts of the plant (flag leaf, foliage etc) and 890 mls is collected on the horizontal surfaces (the ground, other parts of the plant, broadleaf weeds etc). Therefore the selection of a fine droplet rather than a large droplet can allow a six fold increase in the amount of chemical deposited on the vertical surfaces of the plant and it can be concluded that the use of small droplet sizes for applying fungicides is essential. Chemical Manufacturers labels recommend the use of fine droplets for this reason so as to achieve the best results. Aircraft due to their speed have the ability to produce very small droplet sizes when compared with conventional ground equipment and hence make the aircraft a very useful tool in applying fungicides. Fine droplet spraying is also a very effective method for applying insecticides and grass herbicides for the same reasons as mentioned above. As always there is a catch, fine droplets are prone to evaporation and drift.
Dunn Aviation have developed several methods, through 40 years of Aerial Spraying experience, to eliminate these issues. Usually recommending the addition of spraying oils for the control of evaporation. Only applying the spray with a suitable crosswind wind so crop turbulence soaks up the fine droplets. Vary flying height, speed and also changing equipment settings during the day, to compensate for temperature and humidity variation. Coverage Overview Understanding coverage is the important factor when applying fungicides to a crop. The selection of correct application equipment, nozzle setup and water volume is vital for effective coverage. We usually set the equipment on the aircraft to achieve a droplet size of 100 microns (0.001 of a millimetre in diameter which is very difficult to see with the naked eye) and apply 15 litres per hectare water volume as per the original registered manufacturers labels for Tilt, Triad, Folicur and Impact. The label is not a document to be taken lightly and is backed by years of research and yield data. By reducing the droplet size and water volume, we therefore increase the spread factor, and achieve a practical - cost effective application with enhanced chemical efficacy. Spraying Oil Overview Many products that we apply to crops have mineral based carrier solvents included in their formulation. For example when applying one litre per hectare of a Triadimethon based formulation, 875 mls of petroleum based carrier and 125 mls of active ingredient is being applied to the crop for each and every hectare. The mineral based carrier assists the active ingredient to penetrate into the plant so the active ingredient can move through the plant.
Tebuconazole based fungicides have little or no petroleum based carriers in their formulation and are labelled to add spraying oil for enhanced performance, i.e. help penetrate the active ingredient into the plant.
One would therefore conclude that the more oil the better, but as always there is a catch, too much mineral based solvent oil on warm days can burn a crop.
Fine droplet spraying is recommended for and is a widely accepted method for fungicide application. Experience has taught us that using petroleum based carriers at 3% during fine droplet spraying gives excellent evaporation control during spring spraying.
Generally I recommend 15 lts per hectare water volume using 3% spraying oil, this equates to 450 mls spraying oil per hectare. Quite a safe amount when considering the level of petroleum based carriers used in some formulations. If 3% oil is applied at 50 litres per hectare then 1500mls per hectare of spraying oil is applied. Combine this oil level with the existing petroleum based carrier levels in some products and spray on a warm day and some crop burning may be experienced.
If we decided to apply larger droplets and no oil then we start going the other way, the droplets are then not being targeted to the correct destination on the plant and therefore results in less efficacy of the chemical and most importantly less yield. Water volume and oil rates must remain balanced to the prevailing conditions. The preceding document was written by Nev Dunn as an information brochure for clients during the 2003 winter fungicide season.
Droplet Size Overview
Nev Dunn
Ballidu WA 6606
phone 08 9674 1200
facsimile 08 96741266
email: dunnav@bigpond.com
Website built by Jim Robins
Updated 2nd September 2007
jimrobins@bigpond.com