Mahmoud Jokar Amir Masoud Shafiee Pour Abbas Rezaei Asl Shahram Nowrouzieh Cotton Research Institute of Iran, Agricultural Research, Education and Extension Organization (AREEO), Gorgan, Iran Department of Bio-system Mechanical Engineering, Gorgan University of Agricultural Science and Natural Resources, Gorgan, Iran Arthropods ISSN 2224-4255 http://www.iaees.org/publications/journals/arthropods/online-version.asp 2021 10 3 97 107 International Academy of Ecology and Environmental Sciences Hong Kong 18 March 2021 5 June 2021 1 September 2021 Helicoverpa armigera ImageJ UAV water sensitive paper Chemical control is a common way against cotton bollworm (Helicoverpa armigera), a key cotton pest, in developing countries. Therefore, the main objective of current study was to compare the effect of three common sprayers including Unmanned Aerial Vehicle (UAV), Boom sprayer and Hand lance tractor mounted sprayer in controlling cotton bollworm. To evaluated two important spray characteristics such as Volume Median Diameter (VMD) and Percent area coverage (AC) on a canopy, labeled Water Sensitive Papers were installed in three different plant positions (top, middle and bottom) and stain of droplets analysed by ImageJ(R) software. To Assessment of larval H. armigera management, the number of H. armigera larvae was recorded (on 10 random plants per strip-plot) after Thiodicarb (Larvin(R) 75% WP) spraying (before and 1,3,5, 7 and 14 days after spraying). The mortality was transformed by sqrt(x) + 0.1 and analyzed by SAS(R) software. The highest and lowest percentage of coverage belonged to lance sprayer (5.5%) and UAV (2.94%), respectively at the top of plants. Although the spraying characteristics (AC and VMD) of the UAV were not good, the larval mortality on the third day after spraying was 61.1% significantly different from the other sprayer types. UAVs are alternative spraying ways in high-dense cotton canopy fields to save plants and larval management at the same time. http://www.iaees.org/publications/journals/arthropods/articles/2021-10(3)/effectiveness-of-a-sprayer-UAV-controlling-cotton-bollworm.pdf