Eradicants are often used:

Eradicants are chemicals used to eliminate pests that are already present rather than preventing them from occurring in the first place. This makes them crucial in various situations related to pest management.

The reasoning for each context is as follows:

Using eradicants when protectants are too expensive or unavailable is valid because it provides an alternative means to manage a pest situation without incurring significant costs or delays associated with preventive measures. Similarly, if protectants have not been applied on time, eradicants can be utilized to deal with pests that have already invaded the area, ensuring responsiveness in pest control efforts.

Moreover, when a disease breaks out unexpectedly, eradicants serve as an immediate option to combat the issue and protect the surrounding ecosystem or crops from further damage. This adaptability in using eradicants allows for prompt action to safeguard plants or structures, especially in cases where protectants might not have been feasible for initial preventative use.

Therefore, the correct answer encompasses all these scenarios, demonstrating the versatility and necessity of eradicants in pest control strategies.