Passiflora tarminiana
(banana passionfruit)

Although the species P. tripartita var. mollissima (formerly P. mollissima) and P. mixta have been reported as invasive in several countries, notably Hawaii, Australia and New Zealand, recent changes in the taxonomy of these species have meant that the distribution and invasiveness of P. tarminiana and other species of Passiflora is less clearly defined. However, P. tarminiana is now recognized as the only banana passionfruit taxon in Hawaii (HEAR, 2012) and, since its introduction there in the early 1900s, it has spread to infest thousands of acres of native forest (HEAR, 2012). PIER (2012) has assessed its weed risk assessment score at a very high 24.

The species’ climbing habit makes it hard to find and therefore control, and its seed is spread by feral pigs and native birds in Hawaii (PIER, 2012), and by introduced feral pigs and Australian brush-tailed possums in New Zealand (Beavon, 2007). It can spread rapidly and covers the ground, shrubs and even tall-growing trees, preventing regeneration, disrupting ecological processes and threatening biodiversity.

Rejmánek (2009) reported that the species can now be confirmed as invasive in California.

Coppens d’Eeckenbrugge et al. (2001) reported that P. tarminiana is the second most cultivated species in the Andes after P. tripartita var. mollissima (formerly P. mollissima); they found it ‘almost everywhere’ in the highlands of Colombia, the Venezuelan Andes, southern Ecuador and Peru. It has obviously been taken elsewhere – Réunion, California, Ethiopia – for cultivation and possibly also to Mexico and Panama (Coppens d’Eeckenbrugge et al., 2001). The species was presumably deliberately taken to New Zealand and Australia as a potential crop or as a garden specimen.

The risk of accidental movement of P. tarminiana is slight. The most likely avenue of introduction is deliberate actions by humans in importing seed or plants as a potential crop or as a garden ornamental.

P. tarmimiana is often cultivated in the Andes at elevations of between 2000 m and over 3000 m, a greater range than that of its relatives in the subgenus Tacsonia (Coppens d'Eeckenbrugge et al., 2001). Rejmánek (2009) reported that this species is not known from natural habitats but it is cultivated and spreading in disturbed habitats in Venezuela, Colombia, Ecuador, and Peru.

However, in Hawaii, and increasingly elsewhere, its vigorous climbing and scrambling growth makes it an aggressive and damaging invader of forest and scrub once these environments have been opened up by natural or human disturbance (Heenan and Sykes, 2001; Rejmánek, 2009; PIER, 2012; Weeds of Australia, 2012). It has proved capable of smothering even tall forest trees in both tropical and sub-tropical climates. According to Binggeli (1997, in ISSG, 2012), P. tarminiana ‘suppresses tree regeneration, topples shallow-rooted trees, kills standing trees through shading and lowers species richness’.

In Hawaii, Starr et al. (2003) described ‘P. mollissima’ (i.e. P. tarminiana; see Notes on Taxonomy and Nomenclature) as a serious pest in mesic forest between 850-2225 m (2789-7300 ft), on Kauai, Maui, and Hawaii, where it can be found in a variety of habitats including both open and closed forests of black wattle (Acacia mearnsii), koa (Acacia koa), and 'Ohia (Metrosideros polymorpha), as well as mixed native species associations and hapuu tree fern (Cibotium) forests (La Rosa, 1984).

Rejmánek (2009) reported that P. tarminiana has been observed in California 'climbing up to 12 m [high] on trees, including Alnus rhombifolia, Sequoia sempervirens and Umbellularia californica.'

Genetics

Ocampo (2010) reported the chromosome number as 2n=18. Coppens d'Eeckenbrugge (2001) reported that P. tarminiana hybridises readily with other species of the subgenus Tacsonia, producing fertile hybrids with P. tripartita var. mollissima and P. mixta. However, Segura et al. (2005) examined the isozyme variation in P. tarminiana, P. mixta and P. tripartita var. mollissima and found that all accessions of P. tarminiana formed a clearly differentiated group, although some introgression with P. tripartita var. mollissima was suspected.

Reproductive Biology

The species mainly outcrosses, although self-pollination can occur (ISSG, 2012). The large edible fruits contain numerous seeds.

In Hawaii, birds are commonly assumed to pollinate the flowers although La Rosa (1984) found little evidence to support this. In South America, hummingbirds pollinate flowers when probing for nectar located at the base of the long corolla tube. Although many nectivorous birds, both native and exotic, may be found in Hawaii, none possess a bill of sufficient length to gain access to the nectar of P. tarminiana (La Rosa, 1984).

In New Zealand, Beavon (2007) and Beavon and Kelly (2012) observed that germination of the related P. tripartita var. mollissima was effected by honeybees (Apis mellifera) and bumblebees (Bombus spp). They also found that excluding pollinators reduced fruit set considerably. Beavon (2007) suggested that bees are probably much less effective pollinators than humming birds because bees are able to collect pollen and nectar without having to brush the stigma of the large flowers.

La Rosa (1984) examined the germination behaviour of P. tarminiana. Seeds require a short period of after-ripening. Germination is staggered and most seedlings emerge within 4 to 12 weeks. Germination success is not affected by light intensity but the rate increases with higher temperatures that are associated with increasing light. At very low light intensities – 2.0% relative light intensity (RLI) – the germination rate is significantly inhibited.

La Rosa (1984) also found that growth of seedlings was slow by comparison with other stages in the life cycle. Heaviest mortality occurred between germination and the seedling stage. The juvenile phase was characterized by rapid growth (up to 3 m/yr) and distinctive morphology, which can also be found in rapidly-growing adult shoots. Survival from the juvenile to the adult phase of the life cycle is very high. Under favourable conditions, individuals may go from seed to reproductive maturity in a single year.

Physiology and Phenology

Plants can grow from seed to flowering in about one year (La Rosa, 1984). The same author found that in Hawaii all phases of flowering were concentrated in the drier summer months (May - August), and fruiting in the wet winter months (December - March). No strong correlations were found between climatic variables and phenological activity.

La Rosa (1984) observed that net assimilation rates and relative growth rates increased with increasing light intensity. Optimal growth occurred in full sun. Intermediate levels of shade (2-14% RLI) induced etiolation and resulted in rapid height growth, and greatest shade tolerance was exhibited at these intermediate intensities. At very low light levels (0.35% RLI) growth was severely restricted and some individuals were regularly below the compensation point of photosynthesis and respiration.

Longevity

According to Binggeli (1997, in ISSG, 2012), adult plants can reach 20 years of age.

Population size and structure

La Rosa (1984) found that seedling density in Hawaii ranged from 540 to 554,000 individuals per hectare and was considerably higher in areas of heavy pig activity.

Associations

P. tarminiana is commonly grown as a crop in its native Andean range, although wild plants are also found there, having escaped from cultivation. In Hawaii, the principal vegetation types infested with this species include open and closed forests of Acacia koa and Metrosideros collina, mixed native species associations, tree fern forests (Cibotium spp.) and pastures (La Rosa, 1984).

Environmental Requirements

Taken from ISSG (2013):

P. tarminiana tolerates both high and low light levels, although seedlings do not tolerate dense shade. It is tolerant of occasional frosts. P. tarminiana naturally occurs between 2000 and 3600 m above sea level in its native Andes, but can be found growing at sea level in its introduced range. It grows in areas with mean annual rainfall between 800 and 1300 mm and a mean annual temperature of 11.4 to 15.0°C.

As P. tarminiana has proved to be a serious threat to native vegetation in Hawaii and elsewhere, its natural habitat in the high Andes has been searched for its natural enemies. Coppens d’Eeckenbrugge et al. (2001) reported that P. taminiana seemed to be more resistant to fungi than the more commonly grown P. tripartita var. mollissima, and that oidia had not been observed on its leaves nor anthrocnosis necrotic spots on its fruits. They also reported that P. tarminiana is tolerant or resistant to fusariosis. Pemberton (1989) described some of the natural enemies found in South America, some of which have been subsequently tested and a few released in Hawaii. Natural enemies considered for biocontrol in Hawaii by HEAR (2009) include: Cyanotrica necyria, Josia fluonia and Josia ligata (Lepidoptera: Notodontidae); Pyraustras perelegans (Lepidoptera: Pyralidae); Septoria Passiflorae (Deuteromycetes, Dothidiaceae) and Zapriotheca nr. nudiseta (Diptera: Drosophilidae).

Environmental

• Ornamental

Human food and beverage

• Fruits

Other members of the subgenus Tacsonia (especially the very similar P. tripartita and P. mixta) differ from P. tarminiana in having larger, permanently-attached stipules, a longer calyx tube relative to the corolla length, a nectary chamber only slightly wider than the calyx tube, and flowers that are slightly different in colour. Coppens d'Eeckenbrugge et al. (2001) presented a table comparing these three species, which can be found at PIER (2013), and Heenan and Sykes (2003) provided a comprehensive key to the Passiflora species in New Zealand detailing the distinguishing characteristics of P. tarminiana.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

Movement of this species to countries where it does not already occur should be carefully controlled as it has clearly demonstrated its ability to aggressively invade natural ecosystems.

In Australia and New Zealand, members of the public are discouraged from planting the species in their gardens because of the danger it poses to nearby bush areas. New Zealand’s ‘Plant me Instead’ booklets (Weedbusters, 2012) recommend planting the native P. tetranda as an alternative.

Cultural Control

Cattle have reportedly been used to help control P. tarminiana in Hawaiian forests. In Hawaii the plant is often dispersed by feral pigs and has been recorded to decrease in number after the removal of pigs from an area (Scheffler et al., 2012).

Physical/Mechanical Control

Small plants can be hand pulled, but will regrow unless all the roots are removed.

Biological control

Biological control has been long considered the most practical, cost effective and sustainable approach to tackle P. tarminiana invasion in Hawaii. For this reason the native Andean habitats of P. tarminiana have been explored for possible biocontrol agents. Several problems have arisen in the search for suitable biocontrol agents. One has been confusion over the taxonomy of this and related species. Until 2001 the species of Passiflora present in Hawaii was thought to be P. mollissima, but it is now known to P. tarminiana. The early searches for biocontrol agents in the Andes were probably for those that attacked either the more commonly cultivated P. tripartita var. mollissima or P. tarminiana. Another problem has been the need to ensure that the often cultivated edible passion fruit P.edulis is not affected by the agents. 

The first agent to be introduced to Hawaii was the leaf feeder Cyanotrica necyria (Lepidoptera: Notodontidae) from Ecuador and Colombia, which was released in Hawaii in 1988. It established but had no demonstrable effect on the target species (HEAR, 2009).

Josia fluonia (Lepidoptera: Notodontidae), a defoliator, was recommended for release in Hawaii as a biological control agent, but experiments indicated it can survive on edible passionfruit (P. edulis f. flavicarpa). The insect did not appear to have a significant impact on the target plant (HEAR, 2009).

Pyraustras perelegans (Lepidoptera: Pyralidae), released in Hawaii in 1991, feeds on leaves and buds of P. tarminiana. It had little effect. It established on the Big Island, but population levels were extremely variable. The insect may have been unable to overcome the many generalist lepidopteran parasitoids in Hawaii, or it may have been susceptible to a fungus (Metschnikowia sp.) (HEAR, 2009).

The fungus Septoria passiflorae (Deuteromycetes: Dothidiaceae) was released in Hawaii in 1986 and had an apparently dramatic defoliating effect in Laupahoehoe (Big Island), but the cause of defoliation was not confirmed, and drought may have been a factor (HEAR, 2009). According to Trujillo et al. (2001) this fungus had proved to be an effective defoliator of the target weed with no apparent damage to surrounding forest species or to other Passiflora spp. in Hawaii.

In New Zealand, Septoria leaf spot fungus (Mycosphaerella populorum) was trialled as a biocontrol agent but, although the fungus proved to be virulent on the weedy species of Passiflora in New Zealand, it also infected the crop species P. edulis and was therefore not considered safe for release in New Zealand (Hayes, 2005).

Other biocontrol agents have been tested for host specificity and also found wanting because of their likely impact on P. edulis.

Chemical control

Herbicides that give effective control of Passiflora species include glyphosate and metsulfuron. They can be applied by knapsack, brush gun or by the cut stump method. Both herbicides will also kill or damage desirable plant tissue that they contact so they must be applied very carefully. Probably the best method of control involves cutting the vines back as low as possible in winter or early spring and then spraying the regrowth later in spring with herbicide. The cut vines should be left hanging in the tree to dry out before being removed to prevent them from re-growing if they contact the ground, and to prevent damage to the host tree.

For larger plants the cut stump treatment works well. This involves tracing the vines back to the root and cutting them off as close to the root as possible before immediately treating the cut surface with a suitable herbicide. This can be done by applying undiluted herbicide with a paint brush or, alternatively, gel formulations of either glyphosate or picloram are available in some countries.

Biocontrol is almost certainly the best means of control for vines like Passiflora spp. and searches for alternative agents should continue, along with the improvement of methods for testing host specificity and better methods of introducing and distributing such agents.

29/11/12 Original text by:

Ian Popay, consultant, New Zealand, with the support of Landcare Research.