Check your plants frequently under the leaves for egg sacks and remove them immediately. If the damage is visible, lay a cloth under the plants and shake the stems until the beetles fall off the plant. Collect them on the cloth and dispose of them. There are organic sprays that can be used in cases of severe infestation such as Rotenone and Pyrethrum. Always use all pesticides, even organic ones as directed on the bottle.
Improper use can kill off bees and other beneficial insects which are needed in the garden.