How do I rid my spearmint of flies?
It seems as though my spearmint plants are drawing flies. This is the second year the plant has been in my garden, and the first time I've seen the purple flowering. The flies are all over these purple flowers. I've sprayed them with Malathon.
From your photos it looks like the flies may be green bottle flies. We do not recommend spraying Malathion as this is a broad spectrum insecticide that affects pests as well as beneficial insects. Also, you do not want to spray an edible plant with this pesticide.
Many flies land on plants to rest and the flies are not feeding on the plants. These flies may breed in dead animals, feces and/or garbage depending on the species. Locate and eliminate the larval breeding site. To keep the population down make sure they are not laying eggs in trash/garbage cans, pet waste, or in any dead animals in the area. See our publication on flies for more information http://extension.umd.edu/hgic/flies