Error in Inserting the Date + ORACLE

Imports System.Globalization
Imports System.Data
Imports Oracle.DataAccess.Client

Partial Class _Default
    Inherits System.Web.UI.Page

    Dim con As New OracleConnection("Data Source=XE;User Id=user_test;Password=sarvagya;")
    Dim cmd As New OracleCommand
    Dim da As OracleDataAdapter
    Dim ds As DataSet
    Dim query As String

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            query = "Insert into Practise2 values(:DOB)"
            cmd = New OracleCommand(query, con)
            Dim formats As String() = {"dd/MM/yyyy", "d/M/yyyy"}
            Dim dt As DateTime


                cmd.Parameters.Add(":DOB", "TO_DATE('18/07/2011','dd/mm/yyyy')")

            If con.State = ConnectionState.Closed Then
                con.Open()
            End If
            cmd.ExecuteNonQuery()
        Catch ex As Exception
            MsgBox(ex.Message)
        Finally
            If con.State = ConnectionState.Open Then
                con.Close()
            End If
        End Try
    End Sub
End Class