Tradition of applying pesticides has relied generally on using a formulation that mixes with water and is sprayed on crops using manually operated, knapsack sprayers, tractor equipment or aircraft to spray crops to control insect pests, diseases or weeds. The volume of water applied to crops varies but has been over 100 litres per hectare. When rain occurs, the spray deposits on the foliage of crops can be washed off especially from the upper surface of the leaves. The pesticide is therefor moved into the soil and can ultimately it can reach small streams and subsequently rivers downstream. The crop may require another application of spray to maintain control of pests.
The replace of aqueous sprays is to formulate the pesticide using an oil-based liquid so that when rain occurs, the oil formulation remains effectively where spray deposit is attached to the surfaces of the crop.
The oil-based spray is normally applied at an Ultra-low volume (ULV). This can be as low as one litre per hectare. Trials have been carried out using a sprayer fitted with a rotary atomiser to provide droplets, the size of which is within a relatively narrow spectrum to avoid spray drift with very small droplets or wastage to the soil with large droplets. Such trials have enabled yields similar to those achieved when very large volumes of water-based spray were applied.
ULV spraying is particularly important when drones are used to apply pesticides as the spray tank can carry sufficient spray to lengthen the period available for spraying a larger area of crop, without frequent landing to refill the spray tank
Graham Matthews graduated at Imperial College, London as an entomologist in 1957. In 1958 I went to Southern Rhodesia (now Zimbabwe) and Nyasaland (now Malawi) to do research on control of insect pests of cotton crops. In 1967, I returned to Imperial College, but was seconded to Malawi in 1968 to follow up previous research there, which involved a study on ultra-low volume spraying of cotton, as farmers had difficulty obtaining enough water to spray with a knapsack sprayer. In 1972, I returned to Imperial College and remained at Silwood Park campus until I retired in 2001. In 1974 I obtained my PhD and later received a DSc. Over this period I did teaching, including special courses for overseas visitors and research on Pesticide Application and supervised students doing their Doctorate. The research unit was known as the International Pesticide Research Centre (IPARC). I also did tests of different sprayers for WHO in relation to controlling mosquitoes, and since retirement did some training courses for WHO. I visited numerous countries, including Brazil, China, Colombia, Egypt, Kenya, South Africa, Sudan, Tanzania, Turkmenistan and Uzbekistan, to advise on crop protection. Visits to certain countries, including Australia, Cameroon, Ethiopia, India, Malaysia, Nigeria, Pakistan and Zimbabwe were to participate in training courses on pesticide application. I have published several books between 1979 and 2022, notably Pesticide Application Methods, Pesticides, Health, Safety and the Environment, Pest Management, Cotton Pests and their Management, Integrated Vector Management, A History of Pesticides, and Pest Management in Cotton: A Global Perspective.