Alfalfa weevil are generally most damaging in the:

The larval stage of the alfalfa weevil is particularly damaging before the first spring cutting because this is when the larvae actively feed on the new growth of the alfalfa plants. This period, typically occurring in the early spring, aligns with the initial flush of new vegetation that is critical for the plant's growth and overall health.

During this stage, the larvae can cause significant defoliation, impacting the plant's ability to photosynthesize effectively, which is vital for its development. If left unchecked, the damage from the larvae can result in decreased yields and lower-quality forage.

The adult stage, while still harmful, does not typically lead to the same level of damage since adults primarily feed on mature leaves and are less destructive than the hungry larvae feeding on tender young shoots. This underscores the importance of management practices that target the larval stage to protect alfalfa yields in that critical early growth period.