I recommend the utilizing the DateTime.TryParse method before constructing your SQL objects. Ensure you have quality input before having a conversation with your database.
http://msdn.microsoft.com/en-us/library/ch92fbc1%28v=vs.110%29.aspx
Below is a sample from my own code for an asp.net application
// Validation
DateTime dtOut_StartDate;
if (!DateTime.TryParse(txtStartDate.Text, out dtOut_StartDate))
{
Message = "Start date is not a valid format.";
txtStartDate.CssClass = ErrorCssClass.TextBox;
txtStartDate.Focus();
return false;
}