chickens and turkeys?

hello people,

I am Planning to keep chickens, guinea hens and turkeys. me being polyculture supporter, i want to keep them in the same pen.
unfortunately, a book said that if you do this, the turkeys will get a disease and die. is this true?

We've kept chickens, ducks and turkeys all together in the same area but not penned...they were free ranged. No disease or illnesses for any of the birds.

Info on Blackhead Disease: Blackhead

I as well have had no problem with keeping them together as long as they have access to pasture. We keep your turkeys and chickens in a coop together at night, and then in the morning they race for the pasture.

Blackhead is a very serious consequence of mixing chickens & turkeys.
Once established, it is difficult to control/eradicate. The eggs can live in the soil for over 3 years.

However, it is seldom seen in homesteading environments, with lots of open space.
As with many poultry diseases, it is most often a by-product of overcrowding.