Which of the following is NOT a common application method in aquatic weed control?

Soil drenching is considered not a common application method in aquatic weed control because it primarily pertains to terrestrial applications where the pesticide is applied directly to the soil to control weeds or pests. In aquatic environments, the focus is generally on controlling weed growth in water bodies directly, as the applications need to be effective and suitable for an aquatic habitat.

Handgun sprayers, deep water injection, and aerial applications are all established practices used in managing aquatic weeds. Handgun sprayers allow for targeted applications in shallow waters or along the shoreline. Deep water injection is specifically designed to treat areas of significant water depth, ensuring that the pesticide reaches aquatic plants effectively. Aerial applications are commonly employed for extensive areas where physical access is limited, allowing for the efficient coverage of large water surfaces.

Therefore, the use of soil drenching is not typical for aquatic weed control practices, thus making it the correct answer in this context.