What is a defining characteristic of glandular haired-alfalfa?

Glandular haired-alfalfa is specifically characterized by the presence of high densities of glandular hairs on its leaves and stems. These specialized structures serve as a natural defense mechanism against pests, acting as barriers that can deter insect herbivores. The resinous exudates from these glands may be unpalatable or even toxic to certain pests, thus enhancing the plant's ability to survive in the presence of various insect pressures.

This unique trait not only helps in reducing the reliance on chemical pest controls but also contributes to a more sustainable approach to pest management. By leveraging the plant's natural defenses, growers can improve crop health and resilience while minimizing environmental impacts associated with pesticide use. Hence, the defining characteristic of glandular haired-alfalfa is its adaptation to resist pest attacks effectively through its glandular hairs.

The other options, while they may have some relevance in discussions about alfalfa, do not capture the distinctive feature of glandular haired-alfalfa that makes it particularly valuable in integrated pest management.