Not all postharvest diseases produce monocyclic epidemics, but in many cases the infections that result in storage rots have either already occurred before harvest or occur during the harvest and postharvest handling before the product goes into storage. The rot progresses during storage, and new inoculum may be continuously produced, but unless the stored product is handled again to disperse the inoculum and create new infection sites by making small wounds, there are no new infection cycles. Note that the pathogen is not inherently monocyclic but is constrained by the environment to produce only a single cycle of infection. In other environments, these same pathogens might produce polycyclic epidemics.

Fusarium root  rot of bean

Many of the root rots, vascular wilts, and other diseases caused by soilborne pathogens also produce only one infection cycle per crop cycle. The inoculum generally is some kind of survival structure resistant to desiccation or freezing, such as sclerotia, chlamydospores, or oospores in the soil or mycelium in crop residues. This inoculum is dispersed in the soil by plowing and fitting the land and turning under the crop residues. As the roots of the newly planted crop grow through the soil, they encounter the propagules of the pathogen embedded in the soil matrix and become infected. The epidemic progresses as new infections occur, but since any new inoculum that is produced is not dispersed until the soil is again cultivated, there is only one complete infection cycle per cropping cycle. To be sure, not all soilborne plant pathogens produce monocyclic epidemics, and one must be very careful to understand the life cycle of each pathogen before drawing conclusions about its epidemiology.

Demicyclic rusts. Some rusts produce no urediniospore stage (repeating stage) on a single host, and the inoculum produced on one host species generally must infect a different host species. This alternation of hosts appears to have evolved in adaptation to the annual growth cycles of the hosts, and we see one infection cycle on each host per year. An example is the cedar-apple rust, where all the inoculum that infects apples comes from galls on red cedars (junipers), and all the inoculum that infects red cedars comes from apple leaves and fruit. The epidemic on apples occurs during a four- to six-week period of basidiospore production in the spring. A second monocyclic epidemic on red cedars occurs during a brief period of aeciospore production in late summer.

Cedar-apple rust