Which of the following is a drawback of using growth regulators on turfgrass?

Using growth regulators on turfgrass can pose several challenges, one of which is the potential for phytotoxicity, especially in sensitive species such as Kentucky bluegrass. Phytotoxicity refers to toxic effects that certain chemicals can have on plants, which may manifest as stunted growth, discoloration, or even death of the grass if not applied correctly. Kentucky bluegrass is particularly susceptible to these effects due to its specific growth characteristics and environmental preferences.

When growth regulators are applied, they alter hormone levels in the plant, which can lead to unintended stress responses, especially in breeds that are more sensitive to chemical treatments. This underscores the importance of recognizing the compatibility of growth regulators with specific turf species and understanding the proper usage to mitigate any adverse reactions.

The other options either highlight advantages of growth regulators or imply universal efficacy across different grass types, which doesn't accurately represent the nuanced responses different grass species may have to these chemical treatments.