What are products that assist herbicides without being directly toxic to plants called?

The correct choice is adjuvants, which are substances added to herbicide formulations to enhance their effectiveness without being directly toxic to plants. Adjuvants can improve the overall performance of herbicides by increasing their dispersion, absorption, or adhesion to the target plants, thereby ensuring better weed control. They play a significant role in how herbicides interact with the environment, making them more efficient in controlling unwanted vegetation.

In contrast, fertilizers are primarily used to provide nutrients to plants rather than aid herbicides. Regulators typically refer to plant growth regulators that can influence plant development but do not assist in herbicide application or effectiveness. Insecticides are chemicals designed to kill or control insects and do not have a direct role in the application of herbicides. Thus, out of all the options presented, adjuvants uniquely serve the purpose of assisting herbicides in a non-toxic manner to plants.