Early one recent morning in Vidalia, Georgia, US, third-generation farmer Greg Morgan launched an AG-230 drone with 30 litres of fungicide over a field of sweet onions. The chemical, which is essential to crop survival in this humid state, would typically be dragged and dripped from a 1,900-litre tank behind Morgan’s 4.5-tonne tractor. Now it was dropping in a fine mist from the spray jets of a 36-kg drone scudding 10 feet above his cash crop. Vidalia Onions are a $150 million local industry vulnerable to climate change. Morgan has joined the vanguard of farmers who are turning moving from…