Final answer:
Heat, ultraviolet light, and water deteriorate a pesticide's ability to work.
Step-by-step explanation:
The three things which deteriorate a pesticide's ability to work are heat, ultraviolet light, and water. Heat can cause the breakdown of chemicals in a pesticide, reducing its effectiveness. Ultraviolet light can also break down the chemicals in a pesticide, rendering it less potent. Water can dilute the concentration of pesticides, making them less effective.