public function validate($messageManager)
{
$field = $this->form->getField($this->fieldName);
$fieldValue = $field->getValue();
if (!is_null($fieldValue)) {
if (date('Y-m-d', strtotime($fieldValue)) < CoreUtils::getDate()) {
$messageManager->addMessage('dateInThePast', array($this->fieldName => $field->getCaption()));
}
}
}