The most common plant pathogens on ornamental plants in Ohio are fungi, bacteria, viruses, and nematodes. Fungi are by far the most common type of plant pathogens. Plant pathogenic fungi cause many different symptoms, including leaf spots, wilts, curled leaves, dieback, enlargements or galls, and stunted or dead plants. Fungi can spread through rhizomorphs, sclerotia, or by microscopic spores.
Rhizomorphs are rootlike or cordlike masses of hyphae that can contaminate soil and plant parts.
Sclerotia are compact masses of hyphae that can persist for relatively long periods in soil. Sclerotia, rhizomorphs, and some types of spores may survive for long periods in or on plants or in soil. When and where conditions such as temperature, moisture, and the presence of a host plant are suitable for growth, they produce new fungal hyphae and infect the plant. If they are large enough to be seen with the naked eye or a hand lens, signs such as mycelium, masses of spores, and spore-forming structures such as mushrooms, help in identifying fungi. Bacteria are microscopic, one-celled organisms that obtain their food from living plants or other organic matter.