Plants provide us with food and fiber, decorate our yards and gardens, and provide habitat for wildlife. However, when plants grow where they are not wanted, we call them weeds. To home owners, weeds may be unwanted plants in lawns or gardens. To farmers, weeds are plants that interfere with raising crops or livestock. To biologists who manage natural areas, weeds are plants that interfere with the functions of natural communities.
Natural area weeds are often exotic plant species (plants whose natural range does not include Florida and were brought here after European contact, about 1500 A.D.) that have become naturalized (capable of reproducing outside of cultivation). Invasive exotic plants are weeds that alter the functions and value of natural areas by displacing native species (plants whose natural range included Florida at the time of European contact) and disrupting ecosystem services. Natural area managers must remove invasive exotic plant species to maintain the integrity of natural areas.
Air potato is an invasive plant species in Florida that should be removed from public and private properties to help protect the state's natural areas. It has been listed by the Florida Exotic Pest Plant Council as one of Florida's most invasive plant species since 1993 and was added to the Florida Noxious Weed List by the Florida Department of Agriculture and Consumer Services in 1999 (5b-57.007 FAC). Plants on the Florida Noxious Weed List may not be introduced, possessed, moved, or released without a permit.
Air potato can quickly engulf native vegetation in natural areas, climbing high into mature tree canopies (Figure 1). It produces large numbers of bulbils (aerial tubers), which facilitate its spread and make it extremely difficult to eliminate because new plants sprout from even very small bulbils. It invades a variety of habitats, including pinelands and hammocks of natural areas (Langeland et. al. 2008).
Native to tropical Asia and sub-Saharan Africa, air potato was spread by ancient Polynesians throughout much of the South Pacific where it is now considered invasive. It was brought to the Americas from Africa during the slave trade (Coursey 1967), and introduced to Florida in 1905 (Morton 1976). It is found throughout the state from Escambia County in the Panhandle to the Florida Keys (http://www.plantatlas.usf.edu/maps.asp?plantID=1726).
Air potato is a member of the yam family (Dioscoreaceae). Yams are cultivated for their edible underground tubers in western Africa, where they are important commodities. However, uncultivated species—such as air potato—are generally bitter and even poisonous.
How to Recognize Air Potato
Air potato is a vigorously twining herbaceous vine, often arising from an underground tuber. Freely branching stems grow to 60 ft. in length. Stems are round or slightly angled in cross section and twine to the left (counter-clockwise). Aerial tubers (bulbils) freely form in leaf axils (Figure 2). Bulbils are usually roundish with mostly smooth surfaces, and grow up to 5 in. x 4 in. (Figure 2). Leaves are long petioled (stalked), alternate; blades to 8 in. or more long, broadly heart shaped, with basal lobes usually rounded and with arching veins all originating from one point (Figure 3, Figure 4). Flowers are rare (in Florida), small, and fragrant, with male and female flowers arising from leaf axils on separate plants (i.e., a dioecious species) in panicles or spikes to 4 in. long (Figure 4). Fruit is a capsule; seeds are partially winged.
Winged yam (Dioscorea alata), often mistaken for air potato, is similar in appearance and is also a non-native invasive species. Climbing up to 80 ft. in length, stems are square in cross section with "winged" corners that are often red-purple tinged, and twine to the right (clockwise). Winged yam has opposite leaves that are more triangular and larger than those of air potato. Figure 5 shows air potato and winged yam growing alongside each other. Though not as widespread as air potato, winged yam nonetheless ranges from Escambia to Miami-Dade counties (http://www.plantatlas.usf.edu/maps.asp?plantID=1750) and is probably more widespread than has previously been recognized. Winged yam can produce massive edible tubers (Figure 6), some of which have been recorded to weigh over 100 pounds.
Three other introduced species of Dioscorea may be encountered in Florida: Chinese yam (D. polystachya), Zanzibar yam (D. sansibarensis), and wild yam (D. villosa). None of these is considered to be invasive. Our native wild yam (D. floridana) is infrequent in hammocks and floodplains of northern and western Florida, never forms aerial tubers, and has leaf blades that rarely reach 6 in. long.
Controlling Air Potato in Florida
For many years, air potato has been manually controlled by digging the tubers (Figure 6) and collecting and destroying the bulbils produced in the leaf axils (Figure 7). As many bulbils as possible must be removed from infested sites (Figure 7). Those which remain will produce new vines. All plant material, including bulbils, must be disposed of in such a way that they do not spread the vines to new areas (for example, in a landfill or where they will be incinerated). Plants become dormant in winter (during short day-length). Locating and removing bulbils is easier during winter months when air potato and other vegetation are not as dense as during summer. Air potato bulbils cannot tolerate freezing, and placing them overnight in a freezer is the best way to prevent them from starting new infestations. On a larger scale, coordinated bulbil collection events, such as the city of Gainesville's Air Potato Roundup, have resulted in the collection of thousands of pounds of bulbils. These types of volunteer events have been very useful for increasing public knowledge of invasive plant issues and in controlling air potato in many city parks. However, a new biological control for air potato has greatly reduced the need for volunteer efforts in many situations.
The air potato leaf beetle, Lilioceris cheni Gressit & Kimono (Coleoptera: Chrysomelidae), native to Nepal and China, was first released in Florida in 2011 (Figure 8). The insect is specific to air potato and does not harm native plants. The insect has been widely distributed throughout Florida at over 2000 release sites. The air potato leaf beetle feeds on the leaves and causes a skeleton like appearance (Figure 8). The damage can be so severe that aerial bulbil production, the climbing ability, and competitive nature of air potato are all greatly reduced. The insect does not eradicate air potato, but the damage it inflicts makes this insect a growing success story for biological control in Florida. More information on the biology and ecology of the air potato leaf beetle can be found in two additional EDIS publications: Classical Biological Control of Air Potato in Florida (https://edis.ifas.ufl.edu/in957) and Air Potato Leaf Beetle (suggested common name), Lilioceris cheni Gressitt and Kimoto (Insecta: Coleoptera: Chrysomelidae: Criocerinae) (https://edis.ifas.ufl.edu/in972).
For areas where the air potato leaf beetle has not established, the herbicide glyphosate can be used for air potato control. Glyphosate is effective for foliar applications but does not kill aerial bulbils that have already been produced. The high climbing growth also makes foliar treatment difficult for applicators and only partial control is achieved. Additionally, glyphosate is not effective in completely killing the underground tubers, which resprout following foliar treatment. This generally results in the need for multiple treatments. The optimal treatment timing is in the fall, when downward translocation of the herbicide to the roots and tubers is maximized. Air potato is susceptible to frost and poor control is likely if plants experience a cold period just before or shortly after treatment.
Coursey, D.G. 1967. Yams: an account of the nature, origins, cultivation, and utilization of the useful members of Dioscoraceae. London: Longmans, Green and Co. Ltd.
Langeland, K. L., H. M. Cherry, C. M. McCormick, and K. A. Craddock Burks. 2008. Identification and Biology of Non-Native Plants in Florida's Natural Areas, 2nd edition. SP 257. Gainesville: University of Florida Institute of Food and Agricultural Sciences. In press. (http://plants.ifas.ufl.edu/node/613).
Morton, J.F. 1976. "Pestiferous Spread of Many Ornamental and Fruit Species in South Florida." Proc. Fla. State Hort. Soc. 89: 348-353.