You definitely want to explain the grade somewhere in your application. Just briefly explain what happened, and then emphasize the positive (the fact that you earned much better grades later on). You can use the optional essay for this.
However, if you've got something else that you really want to use theoptional essay for (e.g., writing about an important hobby or achievement that didn't fit neatly into another essay), then use the optional essay for the "positive" story that will help make your app more interesting. In this case, you can submit the explanation for your grade in a separate, BRIEF letter.
Veritas Prep | GMAT Prep | MBA Admissions Consulting | Co-author, Your MBA Game Plan
Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
For a limited time, receive access to five Veritas Prep Computer Adaptive practice tests when you purchase a Veritas Prep GMAT book! Buy Now!
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.
Veritas Prep Reviews