«La naturaleza está a menudo escondida,
a veces dominada, raramente extinguida.»
Francis Bacon, 1561.1626, filósofo,
abogado y escritor inglés.

Commelina benghalensis

Una especie de mucho cuidado y que se ha venido diseminando en distintas partes del mundo es Commelina benghalensis L., integrante de la familia de las Commelinaceae, las que se caracterizan por flores funcionales por un día, polinización mediante abejas o avispas, muy atraídas por sus flores, que aparentan tener más polen del que en realidad poseen, fenómeno provocado por sus estaminodios, o sea estambres rudimentarios, estériles o abortados, que en realidad no contienen polen. No obstante, se sabe que algunas plantas de esta familia y género son capaces de autopolinizar. Otra característica es la monofilia, lo que indica que estas plantas han evolucionado de una población ancestral común, donde todos los descendientes están incluidos en la familia.

Los géneros más comunes dentro de esta familia son Commelina con 230 especies, Tradescantia con 74, Aneilema con 60, Murdannia con 45 y Callisia con 20.

Entre las especies más comunes del género Commelina, se hallan Commelina diffusa Burm. f. y Commelina erecta L.,, ambas del hemisferio occidental y muy comunes en muchos cultivos de esas regiones, mientras que Commelina benghalensis L., Commelina forskalaei Vahl son oriundas de África Tropical y del sur de Asia, además de Commelina africana y sus variedades krebsiana  y africana, comunes en África. Todas ellas guardan una fuerte similitud y pueden ser confundidas con facilidad. Una clave al efecto ha sido elaborada por WIKTROP (v. abajo).

C. benghalensis se distingue de las demás por las flores azules, el tallo corto de la flor que no se extiende por encima de la espata, cuyos márgenes están parcialmente unidas y los pelos de color marrón rojizo en la vaina de la hoja. No obstante, C. diffusa, la más común de las demás especies, tiene pétalos azules, pero con la espátula abierta a lo largo de un borde, hojas más estrechas, semillas suaves y sin estolones. Commelina erecta L., también conocida como Commelina elegans Kunth., es capaz de adoptar un porte erecto, mientras que presenta una combinación de dos pétalos azules con uno pequeño blanco, los pelillos en la vaina de la hoja son blancos. C. forskalaei tiene estolones y semillas ásperas, y espátula sellada, pero las hojas son más estrechas, tienen una longitud de hasta 4 veces el ancho y posee bordes ondulados, pero no posee pelillos rojizos en la vaina de la hoja.

Concretamente C. benghalensis o COMBE, comúnmente conocida como la florecilla de Benghal, araña tropical o judía errante es planta decumbente y suculenta, que produce abundante cobertura, sus tallos aéreos son cilíndricos, ligeramente pubescentes, con tallos subterráneos blancos, separados por nudos a partir de los cuales se producen ramificaciones. Rizomas carnosos, blanquecinos, con pocas hojas y flores modificadas, que producen semillas subterráneas formadas a partir de flores modificadas, las que son pocas pero permanecen viables más tiempo que las semillas producidas sobre la superficie del suelo. COMBE posee raíces adventicias derivadas de sus nudos en contacto con el suelo. Las hojas poseen vainas membranosas, protectoras de las yemas, Las flores, como ya se dijo, son espatas de color azuloso. De cada espata surgen tres flores, Sus frutos son cápsulas ovoides, al igual que las semillas.

Su propagación es sexual y asexual. Una planta puede producir más de 1500 semillas, las que usualmente se producen pasadas las primeras 6 semanas de su emergencia, y poseen latencia, cuya germinación se facilita inmediatamente después de la escarificación. Las semillas aéreas son capaces de germinar en los primeros 5 cm del suelo, pero las subterráneas lo hacen hasta 14 cm. Los tallos fragmentados permanecen viables en suelo por varias semanas, aunque si la humedad es óptima forman hojas a las dos semanas.

La planta es perenne en clima tropical o sub-tropical y anual en zonas templadas, lo que demuestra la variabilidad de ploidía, COMBE es hexaploide en medio tropical y diploide en templado. La hexaploide raramente tiene flores subterráneas.

La distribución de la planta aparece en el mapa a continuación elaborado por CABI. COMBE está presente en países con clima templado, tales como Bután, Japón, Corea y Argentina. Se le ha encontrado también en Egipto. No debe confundirse COMBE con Commelina communis L., especie encontrada en varias partes de Europa, incluida Rusia (Webb 1980). En Italia septentrional y en Croacia se encuentra la especie Commelina virginica, la que es oriunda del sur de los EE.UU. El mapa no presenta la presencia de COMBE en Europa, especie vista por primera vez en España por Sanz Elorza et al (2004), pero no encontrada en otras partes de Europa occidental y central. En 2004, Milovic et al (2010) hallaron individuos de COMBE en el puerto de Gazenica (Zadar), Croacia, planta que llegó en cargamentos de soja y cereales. La especie está en esos alrededores, pero afortunadamente no se ha diseminado.  El autor tiene duda que la especie esté reportada en Rusia y que se confunda con C. communis.

Mapa de distribución de Commelina benghalensis (según CABI)

Esta especie suele abundar en todo tipo de suelos y pH, crece en suelos saturados y secos, lo mismo invade cultivos a campo abierto que plantaciones perennes. En India y Filipinas es maleza en arrozales, es muy común en plantaciones de té del Este africano y de India.

COMBE es una especie muy difícil de remover por vía manual, lo cual está dado por ser carácter rastrero. Manualmente lo mejor es desenterrarla conjuntamente con sus raíces y rizomas, algo que es tedioso y lleva tiempo dependiendo de la cobertura existente. Es tolerante a las aplicaciones de glifosato, herbicida que le facilita la competencia con otras malezas, ya que logra predominar en los campos tratados. Paraquat es también ineficiente para su eliminación. Algunos herbicidas fenoxiacéticos como 2,4 D, otros como bentazon y metribuzin suelen efectivos aplicados sobre plantas en sus primeros estadios de crecimiento.

Sobre el control químico, el autor visitó una plantación de cítricos, intercalada con canales para la cría de peces, en Tailandia, donde glifosato se usó bastante y COMBE terminó cubriendo el terreno firme de los árboles. El agricultor buscó consejos para controlar la maleza y se le orientó por algún comerciante local usar fluroxypir, herbicida reportado como de baja toxicidad en peces. Al parecer, el afectado no aplicó bien el herbicida o la dosis no era la adecuada, por lo que al siguiente día de la aplicación, que fue cuando se realizó la visita, una extensa cantidad de peces flotaban muertos en los canales. Por lo tanto, el control químico, con herbicidas no muy conocidos y sin una buena asesoría a la hora de su aplicación, no debe ser practicado para la eliminación de COMBE.

Para control biológico, se ha visto que el hongo Kordyana celebensis afecta tanto a C. diffusa como a C. benghalensis. No obstante, no se sabe si este desarrollo ha continuado.

La planta es usada para alimentar conejos y cerdos en Zimbabwe. En India y Filipinas hay poblaciones que comen la planta, sobre todo en períodos de hambruna, mientras que en casi toda Africa al sur del Sahara se usa para tratar afecciones de la garganta, de los ojos y quemaduras en la piel.

Por su amplia distribución, su ploidía, es conveniente evitar la introducción de la planta en aquellos territorios aún ausente, por lo que se deben chequear aquella importaciones de origen vegetal que vengan de países, donde la especie abunde, en este caso de África y del Asia tropical. Algunos emigrantes africanos, que llegan en pateras a las costas del Mediterráneo europeo, pudieran traer semillas de plantas consigo, con probabilidad de contaminación con semillas de esta maleza u otras inexistentes. En tales casos, lo mejor es tomarlas y destruirlas en el punto de entrada.

Fuentes

Budd GD; Thomas PEL; Allison JCS, 1979. Vegetation regeneration, depth of germination and seed dormancy in Commelina benghalensis L. Rhodesia Journal of Agricultural Research, 17(2):151-154.

Chivinge OA; Kawisi M, 1989. The effect of node numbers on the regeneration of wandering jew (Commelina benghalensis L.). Zimbabwe Journal of Agricultural Research, 27(2):131-138.

CABI. Invasive Species Compendium. https://www.cabi.org/isc/datasheet/14977.

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm

Milenko Milovic, Bozena Mitic y Alegro Antun. 2010. New neophytes in the flora of Croatia. Nat. Croat. Vol. 19(2), 2010

Sanz Elorza M., Dana Sánchez E.D. y E. Sobrino Vesperinas (editores). 2004. Atlas de las plantas alóctonas invasoras en España. Dirección General para la Biodiversidad, Madrid.

Webb D.A. 1980. Commelina L. In:  Tutin, T. G., Heywood, V.H.,Burges, N.A.,Moore, D. M., Valentine, D.H.Walters, S.M.& D.A.Webb (eds). Flora Europaea 5  Cambridge, University Press, Cambridge, p. 117.

WIKTROP. Commelina africana var. krebsiana (Kunth) C.B.Clarke. https://portal.wiktrop.org/species/show/70

Escrito por Ricardo Labrada, 18 diciembre de 2018

“We all have a responsibility to protect endangered species,
both for their sake and for the sake of our future generations.”
Loretta Elizabeth Lynch (83rd Attorney General
of the United States 2015-2017)

The genus Prosopis comprises 44 species worldwide, several of them introduced in Africa, India and Near East in the past 4-5 decades. Prosopis africana is native to Africa, while Prosopis farcta (Syrian mesquite) is found from India to Iran, spread to the Middle East, and occurs in Cyprus, Turkey, Ukraine and along the North African coast as far as Algeria. Prosopis cineraria is distributed in dry and arid regions of northwestern India in Punjab, West Rajasthan, Gujarat, Uttar Pradesh, in dry parts of central and southern India, extending into Pakistan, Afghanistan, Iran, and Arabia, usually at low elevations. The rest of the species are typically native to the Americas and introduced in several arid zones of the world. Inadequate management and lack of good husbandry practices have seen the plant escape from areas of introduction to invade lands previously used for crop production and/or for grazing livestock.

Prosopis juliflora[1] is generally credited as the most noxious of invaders with characteristics that make it a highly successful competitor for land and water. A prolific seeder and with seeds that are highly palatable to livestock, plants It is a thorny shrub, native to Mexico, South America and the Caribbean. It is a contributing factor to continuing transmission of malaria, especially during dry periods when sugar sources from native plants are largely unavailable to mosquitoes. The vulgar names of the plant in their area of origin are bayahonda blanca, cuji y aippia although all these species are called algarrobo. The plant grows to a height of up to 12 m.  and has a trunk with a diameter of up to 1.2 m. Its leaves are deciduous, bi-pinnate, light green, compounded with 12 to 20 leaflets. Flowers appear shortly after leaf development, and are long green-yellow cylindrical spikes. Pods contain between 10 and 30 seeds per pod. A mature plant can produce hundreds of thousands of seeds, palatable to livestock, so mesquite can be spread by ingestion and excretion. Seeds remain viable for up to 10 years. The tree reproduces by seeds. Its roots are able to grow to a great depth in search of water, they were discovered at a depth of more than 50 m. in North America.

Species of mesquite grow successfully in a variety of different environments given properties of self-incompatibility (that promote hybridization), an ability to compete and to suppress other species and the copious quantities of seed produced. Seed remain in a well-protected seedpod with dormancy imposed by a thick seed coat. Seedpods remain unbroken when mature and do not release seed until minimal growing conditions are met. This results in a huge and persistent seed bank in the soil. Similarly, plants have been quick to colonize previously uncontaminated waterways on productive lands. Flood and/or overland flow of seasonal waters can transfer viable seeds many hundreds of kilometres from the mother tree (i.e. seeds are well-adapted to endozochrory or spreading by water).

Grazing livestock help further spread the plant with seeds passing undamaged through the digestive tract of the animals. Mesquite can grow vigorously under the most disadvantaged conditions. It coppices well and was originally appreciated for plasticity, qualities of survival, sand-fixing potential and, not least, for the off-take available to local communities – for fuel wood, construction timber, livestock feed and food for people. For more than 60 years during the first part of the 20^th century the plant has been considered a front-line option for controlling the desertification of farmlands in several dryland areas.

The problem of these species in some of the countries, where they have been introduced:

Ethiopia. Prosopis juliflora has become one of the most serious invaders of agricultural lands since its introduction during the early 1990s. Estimated more than 16 000 ha of reasonable productive lands have been lost to the plant in the Afar and Somalia Regions of Eastern and SE Ethiopia. This is predominately livestock grazing country but the plant has, in addition, successfully occupied cropping lands and infrastructure such as irrigation canals, roads and village areas. The plant is found with moderate level infestation elsewhere in Central and Northern Ethiopia. Prosopis is resilient and adaptable and cannot easily be eradicated by local communities without external assistance.

India. P. juliflora, introduced in 1876, has evolved as a naturalized exotic species in large parts of arid and semi-arid India. It is wide ecological amplitude has contributed for its explosion in saline areas such as Rann of Kutch in Gujarath state as well as the sand dunes of the Thar Desert in Rajasthan. Initially, it was observed to occur in areas of 150-750 mm mean annual rainfall. However, invasions have been recorded in large rice growing stretches of Cauvery River Delta in Tamilnadu state with mean annual rainfall of 1500 mm and where the occurrence of floods and inundation are common. In the southern dry districts of Tamilnadu, where Tank irrigation is the popular and only source of irrigation and village tanks serve domestic water supply, large catchments reservoirs wherein the rainwater during monsoon rains would be stored for use in subsequent drier seasons, have been invaded by of P. juliflora. The species is able to withstand submergence in water for prolonged periods and come up protruding above the water surface with appreciable canopy and branches.

Kenya. The introduction and expansion of Mesquite has followed similar patterns whereby dry land areas in need of environmental protection have been planted with robust cover plants such as Mesquite. For all the best of reasons, those introducing the plant expected to be able to manage it and to handle any issues of invasiveness. Introductions have taken place over more than 35 years. According to the local communities, the main problems attributed to Mesquite are in the following order of importance: long (powerful and poisonous) thorns, invasion and colonization of habitats, elimination of other vegetation, effects on animal health (tooth decay and death from starvation), obstruction/hindrance to communication (blockage of roads, footpaths and punctures), losses in fishing industry, refuge to thieves (including livestock predators and rustlers) and host of crop pests (during intercropping).

South Africa. Several species of thorny Mesquite have become invasive in the arid northwestern parts of South Africa over the past decades. Originally introduced from North and South America in the late 1800s, they were promoted as useful trees and widely distributed and planted until 1960. Widespread, deliberate planting provided multiple sources of seed which were spread far and wide, both endozoochorously and through flooding events. These invasive trees now occur over several million hectares in the Northern Cape, Western Cape, Free State and North West provinces, forming extensive, impenetrable thickets over large areas. Besides overrunning grazing land, consuming excessive quantities of ground water and negatively affecting biodiversity, the plants within dense infestations no longer provide the services that make them useful (i.e. they have no flowers or pods, they are too small and diffuse to provide shade and their trunks are too thin to be useable for timber, fuel-wood or charcoal).

Sudan. Mesquite (Prosopis juliflora) was first introduced into Sudan in 1917. Tolerance to drought and an ability to fix sand dunes quickly made it a success and encouraged further use throughout the country such that by 1938 the plant had been widely introduced into central, northern, eastern and western Sudan. In 1947, a shelterbelt of trees was constructed around Kassala Town – much of it comprising Prosopis. as the result of widespread invasion of natural land habitat and civil infrastructure – watercourses, floodplains, highways, degraded abandoned lands and well-cultivated and irrigated lands, Mesquite has been labeled a noxious weed. Estimates suggest 230 000 ha have been invaded with more than 90 percent of this land in eastern Sudan. This comprises the areas of the Gash Delta to the borders of Eritrea, the Atbara River basin, Khor Baraka and the water collecting areas along the Port Sudan-Gadarif Highway.

Yemen. This country suffers desertification, erosion and soil degradation, and to reduce them, and prevent further degradation and increase soil fertility,  two leguminous shrubs Prosopis juliflora (Sw.) DC and P. chilensis (Molina) Stuntz were introduced five decades ago. These plants were officially introduced into Yemen in 1974, and both species, but more P. juliflora, rapidly spread covering large fertile agricultural and marginal areas. Other species of Prosopis in the country is P. glandulosa Torrey var. glandulosa, in addition to natives P. cineraria (L.) Druce and P. koelziana Burkart normally found in different parts of coastal area of Yemen. The main areas invaded by Prosopis in Yemen are: one in Avian close to Aden, the second in the Hodeidah Governorate and the third one in Hadramut. Mesquite has invaded areas of orchards and sorghum fields, where farmers currently hand pull new shoots of the plants. In a heavy thicket of Mesquite, animals and humans are likely to be pricked by the stems. Barefoot children risk to be seriously wounded if they are pricked by long thorns of the plant. In addition, pollen from Mesquite normally causes allergic reactions in humans. Pods of Mesquite have high sugar content, and animals, particularly sheeps, eating the pods experience teeth decay and die some time later. Agriculture of Yemen is mostly irrigated, and Mesquite spread affects the irrigation canals, where its establishment and growth impedes the correct flow of water. In the regions affected by this species, the main irrigated crops are cotton, onions, watermelons, wheat and various vegetables. The Government has spent more than 2 US$ million for the for the control of Mesquite in the canals before the rainy season. However, the stand of Mesquite is so heavy that the canals are not cleaned at the right time and the normal flow of water is hindered. Acacia is the main tree in Yemen: it is a native plant and it is popular with farmers because of its honey and wood. The people in Yemen assert that honey and charcoal from Acacia are much better than from Mesquite.The reality is that Mesquite is more aggressive in its growth than Acacia, and the latter is being excluded largely by Mesquite. Acacia only becomes green at the start of the rainy season, while Mesquite has the advantage to be an evergreen plant.

Numerous methods have been explored and used for eradication and for preventing infestation of new lands. A key logical feature for control is prevention; with restriction on planting into new areas. Similarly, eradication effort has to be prompt and enduring to prevent newly established plants from taking over. In the low-income countries control is typically a mix of manual clearing and burning. Where additional resources are available, larger-scale mechanical clearing with use of heavy equipment may have a role; and followed by chemical treatment to kill re-growth.

Utilization of Prosopis and products is not generally a method of control, but more one of management tolerance. Communities typically need to be shown how to grow productive stands of Prosopis for the extraction of commercial goods, and to promptly eradicate unwanted growth.

The magnitude of distribution and mass of material produced across complete tracts of land makes Prosopis virtually impossible to eradicate once established. Control becomes an approach that has to be shared within the whole community that people understand the many complex issues for containment, for use of lands that remain vulnerable to encroachment and for intensive management of lands that have been cleared. Given the extent of current knowledge within most rural communities, pragmatism suggests that the tree will continue to extend into new lands during the next period.

Control. Mechanical or manual control strategies are essential to remove dense stands of Prosopis. For manual removal chainsaws or other tools may help, while for mechanical control heavy machinery will be required. Manual removal of unwanted trees is hard work and requires much labour. Mechanical removal requires access to heavy machinery, skilled operators and management and to the fuels, replacement parts and other consumables required of mechanization practices. These are resources that are not typical of small-scale landowners, and normally available from the state. Any removal programme based on the use of large scale mechanization should be evaluated and budgeted prior to beginning – that sufficient resources are available to see the programme through to conclusion.

Land clearance. Mechanical land clearance has been undertaken in Australia with ‘chaining’ land clear of scrub. Chaining is dragging heavy chain stretched between two bulldozers/tractors with a change of direction to ensure that the monotypic woodland stands of Prosopis land cover have been destroyed in two directions (Meadly, 1962). Up to 40 ha can be cleared daily according to Rentz (1993), but this has to be followed up with herbicide treatment to prevent re-growth of suckers. Methods such as this may be effective in some regions but it cannot be recommended more widely, because of the risk of re-invasion by alien plants. Further, there is considerable environmental damage to flora, fauna and to the soils, which are then exposed to the elements. Chaining as a technology for land clearing has fallen out of favour in recent times.

In Yemen, it was found that ploughing killed a high proportion of Prosopis roots. However, some re-growth may follow which will then need to be removed and/or treated chemically. Light ploughing with farm equipment can only handle low-growing shrubbery and then there is the likelihood of damage to tyres and plant. Manual land clearance is a well proven if difficult task, but highly practical where plant infestation is light to moderate. Even here it is more productive to spray auxyn-like herbicides directly on to the plant to hasten the likelihood of kill. Issues of legislation may arise with the use of use of herbicides in some areas.

Burning. Fresh stumps can be treated either with an appropriate herbicide or other means to avoid re-growth. In Kenya, for example, the stump is burned with a mixture of goat manure, twigs and firewood, while in Yemen the application of kerosene over the stump followed by burning has shown to provide good suppression of the plant.

Biological control. To avoid the spread of the plant biological control can be used. The most effective agent and method available is the use of insect seed feeders (such as Algarobius prosopis). In principle, the insect will damage the seeds of the plant – and reduce germination potential – but it will not control it (and, it follows, it will not eradicate the plant from an area).

Chemical control. Basal bark treatment with an herbicide sprayed around the base of the lower stem(s) of the plant is a practice used in the USA. The herbicides commonly used for this purpose are 2,4 D, picloram, triclopyr or mixtures. Methods of this kind may not be feasible in countries where herbicide application is severely restricted; and it may not be practical where people have neither access to the chemicals and equipment required nor to the funds with which to purchase them. Treatments of this kind can only be practised in areas far from other broad leaf crops (that may be susceptible to spray drift) or where there are crops that are generally not affected by the herbicide formulations used.

Replacement crops/cover. It is extremely important not to leave land uncovered after clearing it of unwanted mesquite stands. If there is no natural regeneration then an appropriate forage grass or similar fast-growing crop should be planted across exposed lands. This will help prevent issues of soil erosion and provide competition from regenerated mesquite suckers and runners. Controlled grazing will further limit re-growth.

Prevention. There are other preventative measures available to avoid future problems of mesquite infestation. One logical approach is to strictly prevent the introduction of new mesquite plants into the area – deliberately or inadvertently. Ensure that any livestock moving in from infested areas are corralled and given time to excrete any ingested seeds prior to relocation on cleared and/or non-infested lands. This is simply good land husbandry practice.

Monitoring risk. It is sensible to undertake regular weed risk assessments to evaluate any future problems that may arise from the introduction of exotic plants into new habitats (FAO, 2005). This is normally undertaken with the guidance of specialists from the Ministry of Agriculture-with experienced people able to reject or approve the propriety of newly introduced species (whether Prosopis or other invasive species).

Utilization. It is not a control method, however it is a component of management in areas densely populated by Prosopis is an important component of management. Utilization requires that people are taught to plan and establish suitable gardens of plants and to train them in the correct manner (for the production, for example, of timber).

References

FAO. 2005. Weed Risk Assessment. FAO, Rome, Italy. 16 pp.

FAO. 2006. Problems posed by the introduction of Prosopis spp. in selected countries. Plant Production & Protection Division, Rome, 39 pp.

FAO. 2007. Increased Food Security Control and Management of Prosopis. Proc. Regional Meeting, Awash, Ethiopia, 15-19 Oct 2007.

Meadly, G.R.W. 1962. Weeds of Western Australia Mesquite (Prosopis juliflora DC.). J. Agric. Western Australia. 3, pp.729-739.

Pasiecznik, N. M, Felker, P., Harris, P. J. C, Harsh, L.W., Cruz, G., Tewari, J. C, Cadoret, K. and Maldonado, L. J. 2001. The Prosopis juliflora – Prosopis pallida complex: A Monograph. HDRA, Coventry, UK. pp 162.

Rentz, D.C.F. 1993. Orthopteroid insects in threatened habitats in Australia. In: Gaston, K.J., New, T.R. and Samways, M.J. (Eds) Perspectives on insect conservation, Intercept, Andover, USA; pp. 125-138.

Zachariades C., Hoffman J.H. & Roberts A.P. 2011. Biological control of mesquite (Prosopis species) (Fabaceae) in South Africa. African Entomology Vol. 19, No. 2, pp 402-415.

[1] It is not only P. juliflora, there are other species of this genus also as invaders in Africa and elsewhere.

Additional note: This article has been prepared in English since most of the countries affected by Mesquite are in areas where English is a common language.

Written and prepared by Ricardo Labrada, Dec. 6, 2018

“Estas especies exóticas en el nuevo lugar terminan
desplazando a las especies nativas, ya sea porque tienen
diferentes capacidades competitivas o por la ausencia
de enemigos naturales”.
Dra. Karina Boege Paré, Instituto de Ecología de la Universidad
Nacional Autónoma de México (UNAM).

Una de las especies de planta de mayor diseminación en los últimos 50 años es la asteraceae Parthenium hysterophorus (PTNHY), más conocida como «amargosa, escoba amarga, artemisa o manzanilla» en los países hispanohablantes, o como White top, congress weed y ragweed parthenium en los anglohablantes.

Se trata de una planta oriunda de América Tropical, muy diseminada en la costa atlántica mexicana y en el Caribe, que con el trasiego de mercancías de origen vegetal de un hemisferio a otro, ha logrado establecerse en el sur asiático, en partes de China, Vietnam, Corea y Japón, de África oriental y meridional, así como en Australia y otras islas del Pacífico. Para colmo, la especie ha aparecido en países de clima templado como Bélgica y Polonia, donde se halla en fase de erradicación.

Distribución global de Parthenium hysterophorus (EPPO)

En su área de origen, PTNHY se convierte en un serio problema en aquellas plantaciones tratadas repetidamente con paraquat, mientras que en otras donde se aplica usualmente glifosato, PTNHY es capaz de evolucionar en biotipos resistentes a este herbicida. Con esto debe quedar claro, que el método químico no suele siempre ser la solución para reducir las poblaciones de parthenium a mediano o largo plazo. Igualmente es tolerante a otros herbicidas, como son trifluralin, difenamida y otros utilizados en leguminosas y hortalizas en campo abierto.

PTNHY es una planta erecta anual con hojas alternas, profundamente disecadas, que puede crecer hasta 2 m de altura, con inflorescencias ramificadas que portan cabezuelas florales blancas y aquenios negros, obovoides y suaves. Sus diminutas semillas no suelen germinar inmediatamente después de la germinación, ya que los aquenios antes necesitan dispersarse y liberar algunos inhibidores de la germinación, por lo regular sus máximos de germinación ocurren de 1 a 6 meses después de la maduración. En el Caribe, esta maleza florece a los 30-45 días después de la germinación y el ciclo completo de la planta se alcanza en alrededor de 5 meses, con una producción promedio de 810 cabezuelas florales por planta (Labrada 1988).

Ciclo de Parthenium hysterophorus (Labrada 1988)

Esta planta crece bien en pastos, huertos de árboles frutales y áreas cultivables sobre suelos neutros y ácidos. Gusta de áreas irrigadas, pero es capaz de establecerse en otras menos húmedas. Sus semillas pueden permanecer latentes en condiciones de arrozales con riego por inundación durante años. Una vez se cambia el sistema de irrigación para cultivar otra planta que no sea arroz, PTNHY puede aparecer.

El potencial alelopático de esta planta es alto. Varios autores han reportado la liberación de sustancias fitotóxicas, tales como los ácidos ferúlico, caféico, vanílico, clorogénico, p-cumárico y p-hidroxibenzoico, partenina, ambrosina y coronopilina, inhibidores de la germinación y el crecimiento de algunas plantas cultivables y árboles de multi-propósito. Ese poder alelopático le permite a PTNHY desplazar la vegetación presente y prevalecer en los campos que la misma invade.

También la maleza, al entrar en contacto con la piel del agricultor o de algún animal doméstico, también causa dermatitis alérgica y problemas respiratorios. En este último aspecto de la alergia que provoca en los seres humanos, cabe indicar que el autor sufrió en carne propia erupción de la piel al tocar el follaje de esta planta, pero no al extremo que muestran algunas fotos de la India. Por lo que cabe suponer que el comportamiento de PTNHY sea más agresivo en los nuevos hábitats invadidos.

PTNHY aparece como la maleza más importante en terrenos bajos en Etiopía, y es la peor maleza en las altitudes de la parte oriental de este país.

El control de la planta es factible con labranza profunda en áreas densamente infestadas. En áreas pequeñas de cultivo, la escarda manual durante los estadios tempranos de crecimiento previene la floración, pero debe hacerse tempranamente y así evitar su regeneración a partir de sus yemas en la corona de la planta.

Las áreas europeas del Mediterráneo son un perfecto hábitat para el establecimiento de PTNHY, por lo que debe haber controles permanentes de aquellas producciones agrícolas, sea semillas u otros propágulos de plantas, que puedan venir contaminados con semillas o aquenios de esta maleza. Cargamentos de cereales, semillas de pastos y de otros cultivos anuales de México, del Caribe, de la Florida, EE.UU., así como de la India o Paquistán, pueden ser portadores de semillas de la planta. Si PTNHY logra establecerse en algún punto del Mediterráneo, la erradicación será necesaria y en este caso habrá que utilizar algún herbicida, de forma local, que pueda estar prohibido su uso por la Unión Europea. Los más efectivos sobre esta maleza son: oxadiazon, linuron, fomesafen, ametrina, prometrina y metribuzin.

El control biológico de la maleza es aconsejable cuando hay que sobrevivir con la planta. Los agentes de control efectivos son:

• La polilla perforadora del tallo, Epiblema strenuana (Lepidoptera: Tortricidae), insecto con un nivel de reproducción relativamente alto en cortos períodos de tiempo y su efectividad ha sido comprobada en las alturas centrales de Queensland, Australia.
• El crisomélido, Zygogramma bicolorata (Coleoptera: Chrysomelidae)
• El picudo taladrador del tallo Listronotus setosípennis (Coleoptera: Curculionidae).

Todos estos organismos son originarios del Brasil y México, por lo que requieren evaluación previa en los países afectados por la escoba amarga.

La planta tiene sus atributos medicinales. Por ejemplo, en Cuba, existe una preparación a base de extractos de hojas de PTNHY recomendada pars su uso en el control del insecto Pediculus humanis var. capitis en seres humanos. En América del Sur, sus raíces son utilizadas para preparar una cura de la disenteria amebiana, mientras que en zonas rurales de Jamaica se prepara una decocción de la planta para su uso como repelente de mosquitos.

Fuentes

Basak S.L. 1984. Parthenium – a big threat to agriculture and health in 1980s. Indian Agriculturist 28: 137-143.

EPPO. Parthenium hysterophorus (PTNHY). Global Database. https://gd.eppo.int/taxon/PTNHY/distribution

Labrada R. 1988. Complemento al estudio biológico de Parthenium hysterophorus L. Resumenes IX Congreso ALAM, julio 26-30, Maracaibo, Venezuela.

Labrada R. 1994. Parthenium hysterophorus. Manejo de Malezas para Países en Desarrollo. Edit. Labrada R. C.Parker y J.C. Caseley, FAO. (Estudio FAO: Produccion y proteccion vegetal No 120). http://www.fao.org/docrep/T1147S/t1147s09.htm#parthenium%20hysterophorus%20l.

Swaminathan C., R.S. Rai y K.K. Smesh 1990. Allelopathic effects of Parthenium hysterophorus on germination and growth of a few multi-purpose trees and arable crops. International Tree Crops Journal 6: 143-150.

Escrito por Ricardo Labrada, 21 noviembre de 2018