Which of the following is true about thistles?

Thistles are a group of plants that can be either biennial or perennial, meaning they can live for two years or multiple years, respectively. This life cycle allows them to thrive and reestablish themselves in various environments, making control methods more challenging.

Additionally, their growth habits and ability to produce a significant number of seeds contribute to their persistence and difficulty in management. Effective control often requires a combination of methods, such as mechanical removal and herbicide application, ideally employed before the plants can flower and set seed. Understanding their growth patterns and life cycle is crucial for anyone involved in turf pest management, as it directly impacts the strategies used for effective control.

The other options do not accurately represent the characteristics of thistles; for instance, they are not typically easy to control, and they have various leaf shapes depending on the species, and they do not generally fall into the category of winter annuals.