Increased efficiency is a major focus of today’s aerial applicators.
The techniques of pesticide application have unfortunately not been developed to the same extent as the pesticides themselves. Today the aerial applicator industry in the U.S. is highly favored with the presence of a large number of modern turbine powered aircraft; however, it is used with technology from the near middle ages and to actually disperse the chemicals. Yes, we have sophisticated turbine engines and air conditioned cabins, and yet in most instances we continue to install crude hydraulic spray nozzles from the mid-1950s to atomize the products.
Conclusions from field experience: Low volumes can provide superb coverage provided that the applicator adjusts his application equipment to match the droplet size to the product and conditions. In my view, it’s an absolute necessity to conduct application tests with the equipment and products to identify the optimal adjustment to obtain consistently good results. We need to abandon the old concept of gallons of water and to tailor make applications to match the prevailing conditions.
Proper Measuring Tools
There are several tools that can be used to measure the efficiency of product application. These include the following:
Mylar cards: This is probably one of the oldest methods and in my experience is practically worthless since only the very large droplets, or a few droplets settle within a “no wind” condition will impact and it bears little or no relationship to the real deposit of the product on the crop.
Water sensitive cards: As can be seen in the Graph 1, the popular water sensitive cards have a very low collection efficiency when placed horizontally. The practice of using cards in the horizontal position often leads to erroneous conclusions regarding the effective swath width and the degree of crop coverage. The leaves of the crops are much more efficient at collecting smaller droplets due to their shape and the presence of minute hairs. From an efficacy standpoint all product collected on horizontal cards at ground level within the crop is a measure of lost or wasted product. However, the cards can be used more effectively when inclined at 45 degrees facing the direction of the prevailing wind, with a much higher collection efficiency especially so for the smaller droplets.
Fluorescent tracer products: These types of products permit a visual and photographic assessment of crop coverage and penetration utilizing a “black light” during a night visit to the field. The more effective products are fine powders that are sometimes difficult to mix into a slurry, but are much brighter than the soluble type of product.
Chemical analysis of the deposit: In many respects this technique produces an absolute value, but it does not reflect on the distribution within the plant. The data can still be utilized for crop residue studies and calculation of the “total recovery” of the product within the field.
Individual product performance: Each of the methods has an academic value however the only true measurement that matters on an economic basis is “Did the product work?” In my opinion, we need to seriously consider that we are applying chemical products for a specific purpose to control pests, diseases, or weed control — not painting cards.
Why is this relevant? It is a well-established fact that the pyrethroid insecticides have not been performing as well as expected in many cases, especially within the U.S., yet they continue to deliver excellent performance and are well known for their effect of “rapid knockdown” throughout Argentina and Brazil. The reason is that these products work by contact and ingestion action with no vapor effect, which means that for good results they must be delivered to the target insect. In the U.S., practically all product labels specify high volumes of water such as 2 gallons to 5 gallons per acre. This means that the products are highly diluted with water, furthermore, when applied in high volumes of water most of the product is delivered in large spray droplets resulting in grossly inadequate crop penetration and minimal contact with the insects — so growers have to wait for the insects to find the product.
However, in Argentina and Brazil, most applicators apply the products using low and very low volumes (ULV) typically applying insecticides at 2 liters to 10 liters per hectare (0.1 gallon to 1.0 gallon per acre), with the products being mixed with a non-volatile oil under adverse conditions to protect against evaporation loss.
Rust In Focus
The same principles apply to the control of Asian rust, since for adequate control we must have excellent crop coverage. This can be best achieved through low volumes utilizing oils and adjuvants to minimize evaporation losses and to maximize crop coverage. During the past four seasons very large areas of soybeans in Argentina and Brazil have been treated successfully using low volumes of 2 gallons to 4 gallons per acre using ground equipment and 0.5 gallon to 1.0 gallon per acre by aircraft with results significantly superior to that obtained with high volumes.
The key to success is the production of uniform droplet size and not volume of water. In seeking to obtain increased spray coverage it is far more important and more economical to decrease the droplet size than to increase the spray volume. Many entomologists/agriculturalists have always thought that higher volumes meant better coverage; this is erroneous, as high volumes actually result in poor control with inconsistent results in addition to higher application costs.
Do low spray volumes work? What are the advantages of lower spray volumes? Lower volumes have been proven to be more effective then high volumes in Brazil and Argentina for all categories of application including insect control, rust control, and crop desiccation using glyphosate. Within my personal clients-growers and custom applicators —many million hectares have been successfully treated last season using volumes of 1 gallon per acre or less, with the best results for rust control with aircraft around to 0.5 gallons per acre. With ground equipment, the best results are with 2 to 4 gallons per acre depending on forward speed of the equipment.
Low volumes are more effective for several reasons. The most important is that the chemical ingredient is more concentrated, enabling higher efficacy, in that one spray droplet may be adequate to kill a particular insect. For mechanical reasons, it is easier to atomize a lower volume of liquid using smaller spray nozzles. Rotary atomizers have been proven to be more effective in producing the necessary narrow droplet spectrum; however, they require skill and experience in operation.
In addition, there is longer residual action from chemical deposit. When applied in oils, the products are more resistant to wash-off by rainfall.
Other advantages include higher productivity of the aircraft since less time is wasted refilling with water and in terms of hectares per hour. This also means that spraying can often be finished before mid-day, when the weather is usually less favorable.