Posted: 21/01/2015 at 08:00
Ian, Bob has it right in terms of prevention. Polytunnels can be a fungal trap. Like greenhouses, they can produce fungal diseases all of their own.
If there are spores from last season, they will be on top of the soil having fallen from the leaves. Jeyes fluid won't kill them. Last season's Early Blight spores are only a problem if they splash back up onto new season's plant foliage during watering. Turn the soil over and you will bury any surviving spores. They can't do any damage underground.