This is a puffball. It is a fungus, and a type of mushroom. The name is in reference to the way the spores are disseminated. When pressure is exerted from the outside, as from raindrops or a
small animal passing by, the multitude of spores inside burst like a puff
of dark smoke. Most puffballs are small like a marble or golf ball. But there
is one, the giant puffball (Calvatia) which measures one foot in diameter.
Puffballs feed on organic matter, often times living in the soil on the remains of trees that have been cut down. The puffball as pictured, is the fruiting body of the organism; as mushrooms are. The rest of the organism is thread like, growing in the soil.
They are not plant pathogens, and therefore, no treatment is necessary. Most puffballs are edible. Some larger ones are sold in various markets.
Caution: some puffballs, however, are poisonous. Do not eat any puffballs or other mushrooms that come up in the garden!
Photo: Puffball dispersing it's spores. Wikipedia