I found these paragraphs at the Virginia Tax Dept website in the instructions to Virginia 2018 Form 760 (Resident Individual Income Tax Booklet) at this link:
https://tax.virginia.gov/sites/default/files/vatax-pdf/2018-form-760-instructions.pdf
"Extension for Filing Income Tax Returns: All taxpayers are granted an automatic 6-month extension of time to file their income tax returns. No application for extension is required; however, any tentative tax due must be paid with an extension voucher, Form 760IP, by the original due date for filing the return. You can file and pay your tentative tax online using the Department’s eForms or Individual Online Services. Payments are made electronically and you may schedule payments to be made on a future date."
and
"Extension provisions - Virginia law provides an automatic 6-month filing extension for income tax returns. No application for extension is required. The extension is for filing the return, not for payment of the tax; therefore, you must pay at least 90% of your tax by the due date, May 1 for calendar year filers, to avoid penalty. To make a payment of tentative tax, use Form 760IP."