Opuntia engelmannii
(cactus apple)

O. engelmannii is a species of cactus, and one of many Opuntia species that have been introduced from their native ranges in the Americas and become naturalized and invasive, particularly in Australia, southern and eastern Africa, and the Mediterranean region. However, O. engelmannii is also reported as a noxious weed in Texas and elsewhere in its native range, where it has undergone control for almost a century. Contrastingly, in other US states such as Arizona it is noted as potentially endangered. Noting new records (e.g. Saudi Arabia), further occurrences not yet reported in other countries are possible, and further spread is likely. However, where it is invasive in Australia and South Africa, it has been successfully brought under control, as with other Opuntia species, with the use of biological control agents.

O. engelmannii is native to south-western and some southern and central states of the USA, and to Mexico. In the USA, the centre of diversity appears to be in Texas, where most varieties are reported to occur, but the range spreads from California to Mississippi, and north to Missouri. USDA-NRCS (2015) provide separate distributions in the USA for most of the accepted infraspecific taxa, with O. engelmannii var. engelmannii having the widest distribution, from Texas to California. O. engelmannii var. lindheimeri (=subsp. lindheimeri) overlaps in the eastern part of this range, in New Mexico and Texas, but also stretches east to Louisiana and Mississippi and north-east to Missouri. O. engelmannii var. linguiformis is recorded only in Texas, and thus the centre of diversity for O. engelmannii appears to be in this state.

In Mexico, USDA-ARS (2015) record it as present, and presumably native, to the states of Chihuahua, Coahuila, Nuevo León, San Luis Potosí, Sonora, Tamaulipas and Zacatecas, and south to Guanajuato, Hidalgo and Querétaro.

It has been introduced to Spain, Italy, Saudi Arabia, Kenya, South Africa and Australia, with a further record from Panama. In Australia, it is found mainly in South Australia, around and north of Adelaide, with isolated occurrences in south-western New South Wales and Western Australia (Council of Heads of Australasia Herbaria, 2015). In South Africa, O.engelmannii is reported as spreading and invasive, ‘of particular concern’, and classified as a CARA category 1 weed. O. engelmannii is reported as invasive in parts of Kenya including Loisaba in the north. There are no known records of it in Uganda and Tanzania, although this does not necessarily mean that it is absent from these countries (BioNET-EAFRINET, 2015).

O. engelmannii, like all Opuntia species, prefers hot and dry conditions, and is native to sub-tropical regions in North America. It is more frost tolerant, however, than many other species of Opuntia (Felker et al., 2009). In its native range, O. engelmannii is a true desert plant of rocky or shallow soils e.g. in western Texas, whereas subsp. lindheimeri appears to prefer deeper soils and somewhat more humid conditions as found in central and eastern Texas.

Genetics

Both O. engelmannii and subsp. lindheimeri are hexaploid.

Reproductive Biology

Flower longevity interacts with other variables such as pollinator visitation, temperature and plant resources to control fruit set and seed production of O. engelmannii. Observations in Arizona, USA reported that flowers can open on a single day or on two consecutive days, and that patterns of daily opening and closing appeared to reduce the risk of poor or no pollination (Bowers, 2004). Although flowers opening for the second time offered significantly less nectar and pollen than freshly opened flowers, rewards on the second day were still high enough to encourage visits by potential pollinators (Bowers, 2004).

Visitors to flowers of subsp. lindheimeri reported by Grant et al. (1979) included beetles, which were considered to probably not contribute to pollination, and 10 species of bees, 4 of which are oligoleges of Cactaceae. Small bees (Dialictus and Perdita) were classed as 'pollen thieves', whereas larger bees were effective pollinators, including species of Agapostemon, Melissodes, Diadasia, Lithurge, Megachile, Ceratina and Xylocopa.

Seeds of O. engelmannii that had passed through the digestive tracts of cattle exhibited mean germination rates about 1.5 times higher than control seeds. Germination was improved when temperature was a constant 25-35 degrees Celsius, after soaking in cold water for 12 hours, and after scarification in sulphuric acid (Potter et al., 1984).

Physiology and Phenology

Reproductive maturity occurs after 9-11 years (Bowers, 2005). Flowering in the North American native range is in April and May, with each bloom lasting only one day, opening at about 8 am and closing 8 hours later.

Either flowers or new cladodes are produced from areolar meristems, and plant size was observed to control the number of flowers initiated each spring by O. engelmannii in Arizona (Bowers, 1996). The proportion of flowers that developed and did not abort was thought to be determined by rainfall in the months before flowering, with more developing in wetter years.

Longevity

Individual plants may persist for up to 56 years. Seed can remain viable in the soil for at least 19 months, and probably longer (Bowers, 2005). 

Population Size and Density

Age-based population dynamics of O. engelmannii were studied by Bowers (2005) at a Sonoran Desert site in Arizona, protected from grazing since 1907. Moderate longevity (13-56 years) and per capita annual survival (0.93) were associated with fairly rapid turnover, and cycles of population growth and decline were evident over relatively short periods. Establishment peaks occurred in the late 1970s, the mid-1980s, and early to mid-1990s, coinciding with increased winter moisture in the years before germination, adequate summer rain in the year of germination, and decreased drought in the years after germination, reflecting favorable conditions for fruit production, seed germination and seedling survival. However, even with virtually identical climates, due to local factors, subpopulations a few kilometres apart were seen to exhibit significantly different age structure and density (Bowers, 2005).

Environmental Requirements

O. engelmannii is native to arid and semi-arid regions, often in areas with a short summer rainfall period. However it is also present in the Mediterranean, where winter rainfall is more common. It is reported to prefer clay loams in Texas (Box, 1961), but sandy and gravelly soils in East Africa (BioNET-EAFRINET, 2015). However, the wide genetic variability and broad native range means that varieties will have their own specific preferences. It is one of the more frost hardy species of Opuntia, and hybrids of O. engelmannii have been artificially bred to increase cold tolerance (Wang et al., 1997).

Environmental

• Amenity
• Boundary, barrier or support
• Ornamental

Human food and beverage

• Fruits

Ornamental

• Potted plant

Following Opuntia Web (2014):

O. engelmannii can be readily distinguished from subsp. lindheimeri if side by side. Notable differences include the spines, which in subsp. engelmannii are chalky yellow with orange or red shades and without annular lines, whereas in subsp. lindheimeri they are translucent or shiny spines, never chalky, dull white to dull yellow or brown, and annular lines are generally visible. The bases of spines in subsp. engelmannii may be dark red-brown, brown or black, whereas in O. lindheimeri they may be red-brown, rust-brown with purple or pink shades and only rarely brown or black.

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.

Physical/Mechanical Control

Winter burning of sites infested by O. engelmannnii has been shown to control the plant (Ruthven et al., 2003).

O. engelmannii may be controlled by cutting the main root 5-10 cm below the soil surface, and then stacking all the material in piles to rot. However, Hoffman et al. (1955) considered the use of bulldozers and drags as unsatisfactory, as many pads became scattered in the process, leading to further reinfestation.

In the USA, Gay (1968) reported that light infestations or scattered clumps could be removed by hand-clearing with heavy hoes before piling the plants to decay, or by burning followed by cattle grazing then clearing again. Mechanical clearing of scattered clumps was also successful by tractor, and dense stands were treated by scraping with a bulldozer blade during dry weather or by pulling heavy railroad rails behind or between machines. It was also found better if cattle were fenced into treated areas, to force them to eat regrowth and reduce re-infestation. Reseeding with native grasses may be required if the ground has been highly disturbed.

Contrastingly, Montemayor et al. (1991) found that subsp. lindheimeri density and canopy cover was actually greater in disced areas compared to untreated strips, indicating that discing was not at all effective. Similarly, Gonzalez (1990) found that subsp. lindheimeri density was not reduced by root ploughing, and even the sowing of grass following mechanical brush manipulation had no major long-term effect on brush reinfestation. Furthermore, reinfestation was negatively correlated to rainfall, suggesting faster rate of brush reinfestation in drier years.

Biological Control

The introduced insect agent Dactylopius opuntiae, together with sporadic chemical or mechanical control, was successful in slowing the invasions of subsp. O. lindheimeri in South Africa (Moran and Zimmermann, 1991). Associated factors for success were: the recognition of this species as a weed before it became widely distributed or of much economic importance; timely initiation of biological control; and the presence of O. engelmannii mainly in hot dry areas that enhanced the debilitating effects of cochineal insects on the plants. The reductions in the levels of control observed later were considered to have been due to relatively isolated, refuge populations, which escaped colonization by the biological control agent.

The moth Cactoblastis cactorum has been used as a biological control agent of several Opuntia species around the world and is widely assumed to be a generalist on host plants within the genus. Larval survival from egg to pupation on O. engelmannii was very high at 58, second only to that on O. ficus-indica of all species tested (Mafokoane et al., 2007). The recent arrival and spread of C. cactorum on the North American mainland has raised concerns for the native species of Opuntia that are being utilized as hosts by the moth. To assess these risks, Jezorek et al. (2010) undertook a study aimed at determining if ovipositing females demonstrated a preference for any of 14 common Opuntia spp. native to or naturalized in Mexico and the southwestern USA. Results from a field experiment showed that female moths preferred O. engelmannii var. linguiformis and O. engelmannii var. engelmannii for oviposition.

Cactoblastis cactorum was also reported to have been introduced to Tanzania but it appears to have not become established (BioNET-EAFRINET, 2015). Unidentified cochineal insects have also been observed feeding on Opuntia in East Africa. 

Chemical Control

Much work has been done regarding the chemical control of O. engelmanii and subsp. lindheimeri in the USA, especially in Texas during the past 100 years, and many chemicals and treatments have proved effective. Darrow (1957) found that 2,3,6-TBA was effective as a foliage spray on O. engelmannii, while Kolberg (1969) found MSMA to be effective.

Picloram, when applied either as an undiluted liquid formulation, as granules, or pellets applied broadcast, was found to be the most effective herbicide on subsp. lindheimeri by Meyer and Bovey (1980). Mayeux and Johnson (1989) also found picloram to be effective, although the research showed that most uptake was through the pads, conflicting with the general view that soil applications were more effective.

28/1/15 Original text by:

Nick Pasiecznik, Agroforestry Enterprises, France