Which of the following is not a control method for algae?

The choice indicating that using resistant turf cultivars is not a control method for algae is correct because algae are not directly impacted by plant cultivars. Algae thrive in aquatic environments and are often encouraged by factors such as excess nutrients (especially nitrogen and phosphorus) and poor water circulation. Using resistant turf cultivars can be beneficial for controlling weeds or diseases in turfgrass but won't directly influence algae populations.

Improving soil drainage and copper sulfate application are effective methods for controlling algae. Improved drainage helps reduce stagnant water, making conditions less favorable for algae growth. Copper sulfate is commonly used as an algaecide to directly target and kill algae in water bodies. Fungicide application, while primarily aimed at fungal pests, does not control algae and thus verifies that turf cultivars do not serve as an effective control mechanism for algae compared to other options listed.