Do not confuse Mexican primrose (Oenothera berlandieri) with garden primroses (Primula spp.). Grown in U.S. Department of Agriculture plant hardiness zones 5 through 8, Mexican primrose works well as a ground cover for erosion control. Its delicate pink or purple, cup-shaped flowers are especially appealing in cottage gardens. Despite its delicate appearance, the seeds and roots spread and can take over your garden. Because you're probably too busy to constantly fight aggressive garden plants, use a combination of cultural and chemical weed control methods to get rid of Mexican primrose.
Spray the entire plant with a ready-to-use glyphosate herbicide until the leaves are well coated, but not soaked to the point that it runs off the leaves and onto the ground.
Wait seven to 10 days for the herbicide to dry out the leaves and kill the Mexican primrose plant. Over the course of 10 days, the plant will wilt, shrivel and turn brown. Reapply the herbicide to green parts of the plant if it is not completely killed after the 10-day period.
Dig up the dead plants with a garden trowel or shovel to ensure you remove the entire root.
Pull up new Mexican primrose plants by hand as soon as they sprout. Young plants don't need herbicide treatment because they have small roots that don't anchor in the ground as well as established plants. Monitor the area frequently over the next year and pull up any new plants so you can be sure you have completely eradicated them.