Talk about multitasking: Rhubarb (Rheum x cultorum, Rheum rhaponticum, Rheum rhabarbarum) grows as a vegetable, lends a tropical touch to an ornamental garden and supplies the delightful tang in strawberry-rhubarb pie. Gardeners in search of organic insect control can add one more credential to rhubarb's resume. The oxalic acid that makes its ruffled, rounded red-stemmed leaves toxic to people and pets also kills plant-infesting bugs like aphids when processed into pesticide spray.
Place harvested rhubarb leaves on a cutting board and chop them coarsely with a sharp knife. Clean the board and knife thoroughly when finished so oxalic acid from the leaves doesn't contaminate other food.
Pour 4 cups of water into a ceramic, anodized aluminum or stainless steel saucepan. (Oxalic acid from the cooking damages other metals.) Add the chopped leaves, set the pan on the stove top and bring the water to a boil.
Let the uncovered pan continue boiling for 30 minutes, adding water as necessary to replace what evaporates. Take it off the stove and set it to cool where kids or pets won't reach it.
Strain the cooled liquid into a 2-quart bowl. Using a fine-mesh strainer, press down on the leaves with a large spoon to release all their insecticidal compounds.
Dissolve 2 teaspoons of liquid dish soap in 1 cup of cold water. Add the solution to the strained liquid, blend thoroughly and funnel the mixture into a plastic spray bottle. Label the bottle with its contents and mark it as poison. If any of the mixture is left, store it in a sealed, labeled plastic container away from kids or pets.
Things You Will Need
- Clean, sharp knife (optional)
- Household bleach (optional)
- Chopping board
- 1-quart anodized aluminum, stainless steel or ceramic saucepan
- Fine-meshed strainer
- 2-quart bowl
- Large spoon
- 1-teaspoon measuring spoon
- Measuring cup
- Liquid dish soap
- Spray bottle with blank label
- Container with lid (optional)
- Rhubarb insecticidal spray works well in controlling and preventing aphid infestations, especially on roses. Cover all portions of the plant with the rhubarb insecticidal spray mix.
- If the rhubarb leaf harvest weighs less than 1 pound, make up the difference with grocery-store rhubarb leaves.
- Harvest rhubarb when its stalks are deep red and measure between 1 and 1 1/2 feet long. Rhubarb is perennial in U.S. Department of Agriculture zones 3 through 8, but it won't emerge in spring until temperatures are consistently above 40 degrees Fahrenheit.
- Hand-harvest stalks by grabbing them at their bases and twisting as you pull them up. Alternatively, use a clean, sharp knife cut the stalks as close to the soil as you can without damaging the plant's crown. Expect 1 pound of leaves to yield 1 quart of pesticide. To avoid spreading disease, rinse the knife in a solution of 1 part household bleach to 9 parts water between cuts and after harvesting.
- North Carolina State University Extension: Rheum X Cultorum (R. Rhaponticum, R. Rhabarbarum)
- Pesticide Action Network UK: Aphids -- Least Toxic Control
- Naturally Hamilton: Questions -- Low-Risk Pesticide Products
- Cornell University: Growing Guide -- Rhubarb
- North Dakota State University Extension: Pucker Up for Rhubarb Season