In order to identify "Pythium irregulare" it is necessary to isolate the organism and observe it microscopically. First, it is important to identify that the microbe is an oomycete by looking for characteristics that are specific to oomycetes, such as coenocytic hyphae, zoospores, and oospores. After that, one can identify the microbe as being in the genera "Pythium" by observing disease symptoms, host range, as well as the presence of a vesicle, where zoospores form, which is attached to the sporangia. In contrast, most other oomycetes do not have a vesicle and the zoospores form in the sporangia. Finally, once the genera has been identified, it is helpful to use a dichotomous key to identify the species. Some of the key identifiers for "P. irregulare" include oogonia with irregular shaped, cylindrical projections, sporangia that occur singly, sporangia that are not filamentous, and oogonia smaller than 30 μm. There are also many genomic tests that can be done to determine species based on specific DNA markers. It is also important to note that many diagnosticians do not identify to the species level because it can be difficult to find all necessary microscopic structures and many management techniques can be applied to all "Pythium" species.