Which type of chemical requires more frequent application for effective disease control?

Protective chemicals are designed to form a barrier on plant surfaces, preventing pathogens from penetrating tissues. To maintain this protective layer and ensure ongoing efficacy against diseases, these chemicals must be applied more frequently, particularly in situations where conditions are conducive to diseases or where rain and irrigation can wash away the protective barrier.

In contrast, systemic chemicals are absorbed by the plant and can provide longer-lasting disease control from within, reducing the need for frequent applications. Soil fumigants are used to sterilize soil before planting, and their effects can last for an extended period, also allowing for less frequent use. Herbicides, while needing regular applications based on weed cycles, differ in purpose from disease control and are not focused on protecting plant surfaces from pathogens. This clarity about application frequency and effectiveness helps underscore why protective chemicals require more regular application to manage disease effectively.