"The possible scope of the link between pesticides and adult-onset asthma raises a problem of broader interest, given the considerable quantities of pesticides used in the domestic and urban environments," the Daily Mail quoted a spokesman for the researchers, as saying.
"Their impact on a population which, while less exposed, has a greater risk of allergies and a higher prevalence of asthma, remains to be determined," he said.
These findings will further increase concerns about the impact of chemical sprays on food and the nearness of schools and homes to farms where they are utilised.
Past studies have shown links between asthma, second-hand tobacco smoke, poor diet and obesity.
From the study of 20,000 American farmers it was discovered that farmers who used the maximum amount of pesticides were at the highest risk, after taking their age, weight and smoking history into consideration.
In the due course of the study, 452 farmers aged 30 and above, developed asthma.
The study added that exposure to the pesticide coumaphos doubled the risk of a farmer suffering from asthma.
"Understanding what triggers someone's asthma attack can be immensely helpful when it comes to managing the condition," said Dr Noemi Eiser, of the British Lung Foundation.
"But it also emphasises how important it is for farmers to get themselves checked out and, if they have asthma, to always carry any necessary medication with them," he said.