Bacteria, nematodes, and spores, sclerotia and mycelial fragments of fungi present in the soil are disseminated by rain or irrigation water that moves on the surface re through the soil. All bacteria and the spores of many fungi are exuded in a sticky liquid and depend for their dissemination on rain or irrigation water, which either washes them downward or splashes them in all directions. Raindrops or drops from overhead irrigation pick up the fungal spores and any bacteria present in the air and wash them downward where some of them may land on susceptible plants. Water dissemination is more efficient in that the pathogens land on an already wet surface and can move or germinate immediately. Aphids and leafhoppers are primary vectors for viruses.
Leafhoppers are the main vectors for mycoplasmas and fastidious bacteria.
The Dutch elm disease also depends on the a bug. In these vectored diseases, the pathogen is completely dependent on the vector. Humans -within a field, machinery, tools, airplane. When the host tissue dies, whether an annual or perennial plant, the pathogen survives until the new season. Annual plants- mycelium in infected plant debris, as resting spores, sclerotia, on seeds, tubers.