Generally speaking this kind of fungus is harmless and fairly normal. However if you look very closely at the white stuff and you can see tiny insects hidden in it, then you have a bad case of root aphids. The cure for that is sadly chemical. You would need a systemic insecticide.

If the plants were healthy, this is not a problem - as Owdboggy says, these are fungal based life forms, in fact, mycelium. Many plants have a symbiotic relationship with mycelium and many can't survive or grow well without fungi.

Thank you to Owdboggy and Bamboo, very helpful.

It is true if the plant is healthy everything is fine, also if the plant IS healthy then this “white mold” called mycelium is actually better for the plant and the plants around it. Mycelium is also good for the environment.