You could also do it with your SQL statement,

Code:
            Using con As New OleDbConnection(My.Settings.waterConnectionString), da As New OleDbDataAdapter("Select crop, count(*) as cnt from groups group by crop", con),
                    dt As New DataTable
                da.Fill(dt)

                For Each row As DataRow In dt.Rows
                    Dim str As String = row("crop").ToString & "  " & row("cnt").ToString
                    MessageBox.Show(str)
                Next
            End Using
I tested this on a table called "groups" and a field called "crop". You will need to use your own table and field names.