Most species are plant parasites, but Pythium insidiosum is an important pathogen of animals, causing pythiosis.

[2][6] Many Pythium species, along with their close relatives Phytophthora, are plant pathogens of economic importance in agriculture.

is often limited to the area affected, as the motile zoospores require ample surface water to travel long distances.

Additionally, the capillaries formed by soil particles act as a natural filter and effectively trap many zoospores.

[10] Several Pythium species, including P. oligandrum, P. nunn, P. periplocum, and P. acanthicum, are mycoparasites of plant pathogenic fungi and oomycetes, and have received interest as potential biocontrol agents.