Enable/ disable custom textbox on pageload

Hello, I just added a new custom textbox field to Customer Maintenance. When the page loads, all the controls are disabled by default (except my new custom textbox) until a customer is selected. How can I get my custom textbox to be disabled by default like the other controls unless a customer is selected?

When you bind that textbox to a UD field, it should behave like the other textboxes.