Certified Crop Advisor Practice Exam

Which type of pesticides exert their action when placed on a plant?

1. Systemic

2. Fumigant

3. Contact

4. Herbicide

The correct answer is: Contact

Contact pesticides are designed to exert their action when they physically come into contact with the target pest on the plant. They can kill insects, fungi, or weeds immediately upon application, as they act primarily on the outer surfaces of the plant. This means that for effective control, the pesticide needs to cover the area where the pest is present. Unlike systemic pesticides, which are absorbed by the plant and move throughout its tissues, contact pesticides require direct application on the plant to achieve their intended effect. This characteristic makes them particularly useful for targeting pests that are on the surface of plants. Systemic pesticides, in contrast, enter the plant and are distributed through its vascular system, providing internal protection against pests. Fumigants work by vaporization and penetrate the soil or other mediums but typically do not involve direct surface contact with the plant itself. Herbicides, while they can be systemic or contact-based, specifically target unwanted plants or weeds rather than pests, making contact pesticides the most relevant answer for this question regarding direct action on a plant.