crop duster       
noun [ C ] uk/ˈkrɒp ˌdʌs.tər/ us/ˈkrɑːp ˌdʌs.tɚ/
 喷洒杀虫剂的小型飞机,撒药飞机
a small aircraft used for covering crops with chemicals in order to kill harmful insects and diseases
  He saw a crop duster fly low over his daddy's farm.  他看见一架农用喷药飞机低空飞过他爸爸的农场。 
 - More examples
 - General aviation aircraft range from single-seat crop dusters to Boeing business jets that are as big as 737s.
 - Crop dusters dip and dive and fly just above the ground, leaving signatures in chemicals over fields and orchards.
 - Although crop dusters are occasionally scorned by environmentalists, they also fertilize and plant crops from the air, in addition to spraying pesticides.
 - The town has taken the unusual step of hiring a crop duster to spray lagoons and waste-water treatment plants against mosquitoes.