Ruellia brittoniana

Mexican petunia

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Introduction

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.

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Description

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.

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Impacts

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.            

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Management

Preventative:

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.

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Cultural:

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).

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Mechanical:

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. 

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Biological:

There are no known biological agents for Mexican petunia.

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Chemical:  

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.

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Helpful Notes:

Surfactant – 0.25% is the standard rate for all foliar herbicide applications, 2 teaspoons per gallon.

Dry time – generally 4-6 hours is adequate, but the longer the better for glyphosate

Pay particular attention to herbicide labels near wetlands or bodies of water.

The use of trade names in these publications is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label.

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References and Useful Links:

Unites States Department of Agriculture Naturla Resources Conservation Service Plants Database

Invasives and Exotic Species of North America

University of Florida Center for Aquatic and Invasive Plants

University of Florida’s Cooperative Extension Electronic Data Information Source

Langeland, K.A. and K. Craddock Burks. 1998. Identification and Biology of Non-Native Plants in Florida's Natural Areas. IFAS Publication SP 257. University of Florida, Gainesville. 165 pp.

Pacific Island Ecosystems at Risk (PIER). Plant Threats to Pacific Ecosystems

Floridata Homepage

The Hillsborough County Invasive Species Task Force
Identification and control of non-native invasive plants in the Tampa Bay Area

Krumfolz, L.A. and S.B. Wilson. 2002. Varying growth and sexual reproduction across cultivars of Ruellia brittoniana. University of Florida, Department of Environmental Horticulture. SNA Research Conference, Vol 47, p. 99.

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