Mexican petunia is a plant native to Mexico that grows prolifically in warm regions of the United States. Many gardeners make the mistake of adding Mexican petunias to flower gardens or landscapes without taking steps to contain this wildly spreading plant. If these plants are taking over, eradicate Mexican petunias by applying the herbicide glyphosate. If you prefer to avoid chemicals, eradicate the Mexican petunias by pulling them up by the roots.
Cut the Mexican petunia plants down to 1 or 2 inches above the soil level during the growing season. Dispose of all of the plant foliage in the garbage bag.
Choose a day that is sunny, above 60 degrees and calm. Apply the glyphosate to the remaining stems of the Mexican petunia plants. Saturate the entire growing area thoroughly, but make sure you do not overspray any other planting areas.
Monitor the Mexican petunia plants during the next three to four days. If you do not see obvious wilting and yellowing, reapply the glyphosate a second time to ensure you eradicate the plants.