They are fungal-like because of their similar life cycles, but differ in that the resting stage is diploid, they have coenocytic hyphae, a larger genome, cellulose in their cell walls instead of chitin, and contain zoospores (asexual motile spores) and oospores (sexual resting spores).

[1] Pre-emergence damping off occurs when P. irregulare infects seeds before they emerge, causing them to rot and turn brown, thus preventing successful growth.

[3] This will initially cause necrotic lesions, which leads to chlorosis, reduced yield, poor growth, and stunting due to inadequate water and nutrient acquisition by the roots.

[2] After that, one can identify the microbe as being in the genus Pythium by observing disease symptoms, host range, as well as the presence of a vesicle, where zoospores form, which is attached to the sporangia.

[7][8] Pythium irregulare has a very broad host range, including many agronomically and horticulturally important crops and is found on every continent except for Antarctica.

[8] Alternatively, the hyphae within the dead plant material may also continue to grow and develop “male” and “female” haploid mating structures, known as antheridium and oogonium, respectively.

[1] The antheridium then transfers its genetic material to the oogonium (fertilization), resulting in the diploid oospore, which overwinters and starts the infection over again in the spring.

Pythium irregulare requires very specific environmental conditions to produce disease, so control of environment is the first step.

[4][8][9][10] Additionally, in greenhouses scenarios it is important to sanitize soil, work benches, and tools with heat or chemicals as well.

[8] Finally, if you have had previous problems with Pythium irregulare, you can take preventative measures by mixing fungicides into the soil, although this is more easily achieved in a greenhouse scenario.