Which of the following is a method for applying pesticides?

A backpack sprayer is an effective method for applying pesticides. This tool allows for precise application, which is important for targeting specific areas and minimizing drift. The backpack sprayer is versatile, enabling users to apply various types of pesticides, including liquids, in different formulations tailored to the treatment needs. Its design provides mobility and ease of use, allowing the applicator to reach plants and spots that might be difficult to access with larger equipment.

The other options, while they may serve specific purposes in gardening or turf management, are not suitable for applying pesticides efficiently. A watering can is generally used for watering plants and might not provide the desired precision or coverage for pesticide application. A grain spreader is designed for spreading seeds or granular fertilizers and would not effectively apply liquid pesticides. Similarly, a fertilizer injector is meant for injecting fertilizers into irrigation systems, not for pesticide application. Thus, the backpack sprayer stands out as the most appropriate method for pesticide application.