Mexican petunia is another example of plant that is being sold over the internet and in garden centers as a flowering plant or “handy perennial edging plant for flower beds and as colorful groundcovers”. The problem is that the Mexican petunia is highly invasive and is listed as a Category 1 invasive species by the Florida Exotic Pest Plant Council. Mexican petunia received this classification because of its invasion and distribution within native plant communities.
Mexican petunia can thrive in a range of environments, including flatwoods, hardwood hammocks, prairies, rivers and pastures. The cultivars available for sale in the trade have been selected for their flower color or size (tall or dwarf), however there have been very few research projects dedicated to determining the invasive characteristics of the cultivated varieties.
Mexican petunia is a stalk forming perennial that stands up to 3 feet in height. Leaves are dark green; oppositely arranged and lance-shaped, roughly 6-12 inches long and 1/2-3/4 inches wide. Veins are prominent on the underside of the leaf. Leaf margins are can be smooth or wavy. Foliage appears a metallic blue/purple under full sun. Flowers are trumpet shaped (1 1/2 -2 inches in diameter), solitary or borne in clusters at the tips of the stems. There are numerous varieties with a plethora of color to choose from (white, pink, and many shades of blue). Dwarf varieties are also available. Cylindrical fruit containing 4 to 20 seeds are produced. Mexican petunia is capable of reproducing and spreading via seed, rhizomes, stem sprouts and cuttings.
Mexican petunia is able to tolerate a wide range of environmental conditions including variations in light, temperature, and moisture. Other characteristics that make Mexican petunia a successful invasive are its rapid growth rate, affinity for disturbed locations, prolific production of seed, and lack of germination requirements such as scarification. Mexican petunia can also resprout from crowns or rootstocks when cut back or killed back by frost.
Regular monitoring and rouging of plants can prevent the spread and establishment of Mexican petunia. Programs to educate homeowners on alternative plants to Mexican petunia in landscape settings will also reduce the spread of this species.
Native alternatives to Mexican petunia for use in home landscaping include wild petunia (Ruellia caroliniensis), blue curls (Trichostema dichotomum), butterflyweed (Asclepias tuberosa), or swamp milkweed (Asclepias perennis).
Hand-pulling and removal of entire plants is practical for small infestations. Aggressive tillage and mowing is effective, but impractical in many situations. Germination from seeds after tillage is likely, so follow-up control will be necessary.
Timing of application is critical to effectiveness. Foliar applications of glyphosate (1-2%) or cut back plants then treat with glyphosate. Evaluations of alternative herbicides for Mexican petunia control are currently being conducted.
Excerpted from the University of Florida, IFAS Extension, Circular 1529, Invasive Species Management Plans for Florida, 2008 by:
Greg MacDonald, Associate Professor Jay Ferrell, Assistant Professor and Extension Weed Specialist
Brent Sellers, Assistant Professor and Extension Weed Specialist
Ken Langeland, Professor and Extension Weed Specialist Agronomy Department, Gainesville and Range Cattle REC, Ona
Tina Duperron-Bond, DPM – Osceola County
Eileen Ketterer-Guest, former Graduate Research Assistant