Air potato
Scientific: Dioscorea bulbifera L.
Common: air potato, potato yam, aerial yam, air yam, bitter yam, cheeky yam, bulbil-bearing yam
Family: Dioscoreaceae
Introduction History: Native to Africa and Asia [4, 21, 25, 37]. Introduced to Florida in the early 1900s as an ornamental and food plant [23, 30].
General Description: Perennial, counter-clockwise twining vine typically found growing into tree canopies [8]. Sometimes produces spherical tubers within the top few inches of soil. Produces brown or tan aerial bulbils (>2 inches diameter) along the stem at the leaf axils [11, 14, 25, 30].
Habitat: Occurs near ponds, marshes, drainage canals, in disturbed woods and thickets, forests, floodplains, waste areas, and urban landscapes [30]. Can invade undisturbed habitats, but it is less common in pine woods and coastal areas [11]. Prefers moist soils high in organic matter [21].
Invaded Range: Most widespread species of Dioscorea globally. In the United States, it is present in TX, LA, MS, GA, HI, PR, and FL [27, 39]. Most abundant in central and south Florida, due to more mild winter temperatures [11, 27]. Also present in other tropical and subtropical regions globally.
Leaves: Ovate-cordate leaves 2-10 inches in length and width, alternately arranged with prominent venation (5-11 main veins) and glabrous surface. Leaf base orbicular. Petiole with clasping base. Leaf margins entire. Apex long-acuminate [30].
Flowers: Dioecious – distinct male and female individuals. However, Florida populations are dominated by female plants, so sexual reproduction is rarely observed [12]. Inflorescences produced axillary. Pistillate inflorescencesare singly or in fascicles up to 6 per axil, spicate. Spikes measure 2-16 inches with 50 flowers irregularly arranged. Flowers are not showy with greenish-white perianth. Flowering occurs between late summer (July) to early fall (September) [30]..
Fruit: Trilocular, capsule fruit measuring up to an inch long and usually about 0.5 inch wide [8, 11, 14, 30].
Seeds: Unilaterally winged seeds measuring less than an inch [30].
Other (Congeners):
Superficially similar in appearance to herbaceous Smilax clade (Nemexia) but readily distinguished by the following: Smilax (section Nemexia) has 3-5 main veins, the central 3 veins rejoining at the leaf apex, and secondary veins form a reticulate pattern; Dioscorea has 7-13 main veins, and secondary veins form a simpler pattern mainly perpendicular to main veins.
Within the Dioscorea genus, there are two natives and five invasive species known to be present in Florida (See 11 or 27 for detailed comparison).
The two natives (D. floridana and D. villlosa) are both rhizomatous, lack bulbils produced at the leaf axil, leaf margins are entire or repand, petiole bases not clasping, and produce inflorescences regularly. D. floridana and D. villlosa are present only in north and central Florida [42].
D. dodecaneura, D. polystachya, and D. sansibarensis are considered eradicated in Florida [27] and easily distinguished by leaf color or lobed leaves [42].
D. alata is distinguished by its broadly winged, 4-angular stems, opposite or suboppositely arranged leaves, and seeds winged all around. Compared to the terete, usually unwinged stem, alternately arranged leaves, and seeds with only one wing [11, 42].
Listed as a State Noxious Weed in Florida (FDACS). Not currently listed as a Federal Noxious Weed. UF IFAS Assessment “Prohibited”. FISC Category I.
Do not move propagules (tubers or bulbils) of air potato. Report infestations in natural areas to responsible managers. Responsibly dispose of any reproductive plant material through incineration, freezing, or municipal yardwaste/landfill if local facilities are equipped to do so.
Mechanical control methods can be used to reduce spread and asexual reproductive potential, and therefore should be a first step approach to the management of air potato. Manual control techniques consist of cutting climbing vines, excavation of tubers, and removal of bulbils. Vines should ideally be cut prior to bulbil formation (typically late summer). Collection of bulbils is most effective in winter months when they are more easily located due to the lack of dense vegetation. Viable plant material (tubers and bulbils) must be responsibly disposed of to prevent further spread [12]. These methods combined with follow-up treatments yield the most consistent success.
There are currently two biocontrol agents introduced to Florida for controlling air potato; air potato leaf beetle (Lilioceris cheni) and Lilioceris egena.
The air potato leaf beetle (Lilioceris cheni) is established in Florida and suppresses air potato through vigorous herbivory of the leaves. This reduces the growth potential and asexual reproductive capability of the plant [6, 7, 10, 12, 20, 29, 34, 41].
Lilioceris egena predates on the bubils of air potato [24, 29].
There exist varied results from chemical treatment research for the control of air potato [27].
Foliar:
Foliar applications are recommended for controlling air potato and best applied late in the growing season (August-October) [18]. Reportedly effective herbicides include:
Glyphosate: 1-3% v/v [12, 28]
Triclopyr amine: 1.5% v/v [13]
Cut-stem:
Vines which have been cut at the soil surface can be controlled with subsequent chemical applications carefully applied to the cut surfaces. Reportedly effective herbicides include:
Triclopyr amine: 50% v/v [3, 16]
triclopyr ester: 10% v/v [3, 16]
This approach may be useful in situations where target plant foliage is not accessible by applicators (growth into canopy) or non-target plant foliage is heavily mixed with air potato vine.
Basal bark:
Although not a trunked plant, directed applications of oil-carrier solutions may be effective for controlling air potato when applied to bulbils or exposed tubers [3]. Such methods would only be applicable in areas with exceptionally dense or remote populations of air potato such that manual collection and disposal of bulbils is not practical. Non-target damage and herbicide drift risk is high with this method, especially in areas prone to flooding.
Frequency and Timing:
Repeated annual chemical treatments over 4-5 years are essential to ensure all potentially viable propagules are eliminated [12, 18, 27]. Differences between trialed treatment timing may suggest that triclopyr may be more effective for earlier season treatments, while glyphosate is more effective for late-season treatments [27].
Depending on the vegetative community present at the target site, certain herbicides may cause damage to non-target plant species. Furthermore, dense growth into tree canopies may cause logistical issues with foliar treatment. Earlier treatment timing will help mitigate these issues.
