Farmgirls. Worms are in the soil anyway, there's not much you can do about getting rid of them. Worms are in/on the grass they eat, bugs,lizards etc... This is why you should have a routine worming program. I worm twice a year because I live in a swampy area that's condusive for worms. If you live in a more dry environment, it might be only necessary to worm them once a year. Dont always use one wormer, this can cause worm immunity over time. Use different wormers each time you worm your chickens. DE is good for drying out wet or damp chicken runs/houses and can be used to prevent lice/mites. DE will not kill worms, it is useless when wet. To use DE everywhere on the ground to kill oocysts is nearly impossible, very cost prohibitive especially free ranged flocks.
