Dunno why I haven't had gnats for years...might be the diametaceous earth and no pest strip sittin in the corner of my veg area that's renewed bout every 6 months. DE is used if necessary in the flower areas. The only time I've had any infestation was years ago with spidermites brought in from a friends infected grow and gnats brought in by poorly housed soils...that was enough for me...no problems since. Seems the veg area treatment kinda inoculates the plants for the flowering period...