How to Subtract the score

Hey guys, I'm making a prototype game for one of my uni module's. Its a simple game where the player has to try and catch the spawning object. I've got the score to increment by 1 but how do I go about taking the score away if the player misses the object.

code using UnityEngine; using System.Collections;

 public class Score : MonoBehaviour 
 {
     public GUIText SugarProductionText;
     private int SugarProduction;
 
 
     // Use this for initialization
     void Start () 
     {
         SugarProduction = 0;
         SetSugarProductionText();
     
     }
     
     // Update is called once per frame
     void OnTriggerEnter(Collider other)
     {
         if(other.gameObject.tag == "Sugar")
         {
             other.gameObject.SetActive(false);
             SugarProduction = SugarProduction + 3;
             SetSugarProductionText();
         }
         else if(other.gameObject.tag == "Terrain")
         {
             other.gameObject.SetActive(true);
             SugarProduction = SugarProduction - 1;
             SetSugarProductionText();
         }
     }
 
     void SetSugarProductionText()
     {
         SugarProductionText.text = "SugarProduction" + SugarProduction.ToString();
     }
 }

I tried applying a tag to the terrain, so if the object spawning touches the terrain the player score would go down, but it doesn't.