Let me begin by saying my Veterinary Knowledge on geese is not so good since I am into dogs and cats treatment, but I have an opinion.
There is a worm that affects turkeys, found in the intermediate hosts that are worms(Nematodes easily found on the ground )picked from the ground.
The domestic fowl is also involved in this life cycle. The protozoa causing this disease is Histomonas Meleagridis. Worm called Heterakis gallinarum , that is regularly eaten by the Domestic fowl from the ground .
Often the disease is called the Blackhead Turkey Disease. You can read more about the disease from Wikipedia
Based on this argument you should implement the following effective control measure for your geese:
Dimetridazole can be used in the drinking and feeding troughs
Cleaning premises and ensuring Bio Security measures are implemented in the Farm.
Dead Birds should be buried or burnt after PM examination
I hope this partially answers your question