Key Microorganism: Oomycetes

Also known as water molds, Oomycetes are filamentous organisms that resemble fungi, however they are not true fungi. Although they can take on roles as either saprophytes or pathogens, they have a cell wall composed of cellulose instead of chitin, as with fungi, and include some of the most notorious plant pathogens such as downy mildew, blights, phytophthora, pythium, etc.

Sporangia and sporangiophores protruding from the stomas of the grape berries. By David S. Jones, Patricia McManus - UW-Extension, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=45343445

Recommended levels

Along with oomycetes, we also include the biomass for potential disease-causing fungi in this group because they closely resemble one another morphologically and are indicators of anaerobic conditions. Their biomass should always be less than ¼ that of beneficial fungi.