Yes. Log in to the mobile app and click the “Cards” icon in the lower navigation bar.   Locate the Card you’re looking for in the list, then slide the green toggle for that Card to the left. This temporarily disables the Card and prevents it from being used for purchases.
To permanently disable a card, click on the three dots in the upper left corner of the Card, then select “Block Card” from the list of options. The app will guide you step by step through the process.