The leaves of a rhubarb plant will effectively battle insects like spider mites and aphids in the garden. Once you save the leaves of the rhubarb plant, they need to be steeped in boiling water to remove the oxalic acid. The oxalic acid works to kill the insects on your plants, but the leaves and solution need to be handled carefully because the acid is also dangerous to humans. The solution can be applied to your plants as needed to control the pests.
Wear rubber gloves to protect yourself from the poisonous leaves. Chop 0.454kg. of rhubarb leaves with a sharp knife.
Fill a cooking pot with 1 qt. of water.
Add the rhubarb leaves. Boil the water and leaves for 30 minutes.
Add 1 tsp of liquid dish soap to the water.
Place a bowl under a sieve. Strain the solution into a bowl, and discard the rhubarb leaves.
Pour the solution into spray bottle. Spray the solution onto the plant. Cover the undersides of the leaves, stems and canes to control the insects. Wear gloves when applying the spray to avoid contact with your skin.
Never apply the rhubarb spray on edible plants as the solution is poisonous and can cause death or severe illness when ingested. Always wash your hands and cleaning utensils with warm and soapy water after handling the rhubarb leaves.