Which statement is true regarding the control of monocyclic diseases?

The correct answer highlights the nature of monocyclic diseases, which are characterized by having only a single infection cycle per growing season. The primary inoculum is the initial source of the disease, and if it is effectively controlled, the disease cannot initiate or progress further. This means that by managing the primary inoculum, growers can often prevent the disease from developing altogether, since there are no secondary cycles to perpetuate the infection. Thus, controlling the initial source of infection is a crucial strategy in managing monocyclic diseases.

In contrast to this, the other options focus on aspects that don't align with the nature of monocyclic diseases. For example, the need for controlling both primary and secondary inoculums is more applicable to polycyclic diseases, where multiple cycles can occur and secondary infections play a significant role in disease spread. The statement regarding intensive chemical treatments does not reflect the typical management strategy for monocyclic diseases since, once the primary inoculum is dealt with, there is often less need for ongoing treatment. Furthermore, stating that control can be achieved after multiple infection cycles does not apply to monocyclic diseases, as they do not have multiple cycles in a season to manage.