Hello, 

The basil is safe to use if you have used the 'Concentrate' formula for rose, listed fruit, and listed veggies and you applied the amount on the label. Basil is on the list of crops it can be used on, and it can be used until day of harvest.  I do not find basil on the 'Ready to Spray' formulation label.

If the dark leaf spot on the basil is a result of the spray, it means the plant is sensitive to the spray. The fancy name for that is phytotoxic. If you used the Ready to Spray formula, that is probably why it affected the plant.

The label on all pesticides is the place to find out what you can spray and how much to spray on your plants.  It is also the law. You should read and follow the label carefully.