Poison sumac (Toxicodendron vernix) contains a toxic chemical called urushiol in its sap. All parts of the plant are poisonous, and the sap causes severe irritation when it comes into contact with bare skin. For this reason, the plant, which is hardy in U.S. Department of Agriculture plant hardiness zones 3b through 8b, is considered highly undesirable.
Killing it with Chemicals
Using glyphosate may be the most common way to kill poison sumac, but many home gardeners prefer homemade, non-toxic choices. Although glyphosate is considered safe for use around children and pets, it is very toxic to aquatic life. A substitute for herbicides that contain glyphosate is vinegar.
Using Vinegar as an Herbicide
A study by the U.S. Department of Agriculture (USDA) Agricultural Research Service concluded that vinegar is effective in killing weeds. It's the acetic acid in the vinegar that makes it so deadly to plants. Household vinegar usually contains 5 percent acetic acid. Vinegars with higher acetic acid percentages -- up to 20 percent -- were much more effective in killing weeds. Killing poison sumac may require using a food-grade vinegar that has a 20 percent concentration of acetic acid.
Mixing Up a Homemade Weedkiller
A homemade weedkiller solution containing vinegar can be made by mixing about 4 ounces of lemon juice with 1 quart of vinegar. White or cider vinegar can be used. Mix the two liquids together, and place the resulting solution in a spray bottle. Spray the poison sumac with the solution on a hot, dry day, coating the plant's leaves with the spray as thoroughly as possible. Reapplying the spray daily until the plant dies may be necessary.
Getting to the Root of the Problem
Unfortunately, the USDA study found that vinegar is more likely to kill small plants than large, established plants. A University of Washington Botanic Gardens website article states vinegar kills plant leaves but not roots; small plants die after contact with vinegar because their small root systems don't have enough stored energy to regrow, and more vinegar applications may be necessary to kill larger plants. Poison sumac can grow to a height of 20 feet, which means a full-grown plant probably will not be killed easily by any homemade weedkiller. If you want to get rid of a mature poison sumac tree, consider hiring a professional tree removal company.