how to use onCollision with Application.LoadLevel

[RavenMats3r]

i am trying to make a 2d game where the level ends after you hit a flag.
right now i have this code:
using UnityEngine;

public class endflag : MonoBehaviour
{

    // Use this for initialization
    void OnCollisionEnter(Collision col)
       {
        if (col.gameObject.name == "turtle")
        {
            Application.LoadLevel("mainMenu");
        }
    }
}

from everything i have looked at this should work
(the code is on the flag and the players name is turtle)
did i write something wrong or should i have the code on the player instead

[TBruce]

Application.LoadLevel() is obsolete you now need to use SceneManager.LoadScene(). To use the SceneManager class you need to add the UnityEngine.SceneManagement namespace to the uses clause.

using UnityEngine;
using System.Collections;
using UnityEngine.SceneManagement;

public class endflag : MonoBehaviour
{

    // Use this for initialization
    void OnCollisionEnter(Collision col)
    {
        if (col.gameObject.name == "turtle")
        {
	        SceneManager.LoadScene("mainMenu");
        }
    }
}