OF parthenium CONTROL
Ever since the weed became a menace in different parts of the country, several methods are being recommended in containing the growth of parthenium. But none of them appear to be satisfactory, as each method tried during the period from mid sixties to eighties suffered with one or the other limitations such as inefficiency, high cost, impracticability, polluting the environment, temporary relief etc. However, integrated approach recommended in the late eighties seems to be promising. Thus various methods - manual, chemical, biological and integrated methods together with their merits and demerits are discussed in this article. Further, people need to be aware of how the weed spreads in order to take preventive measure to contain it. Therefore, field days, awareness camps and meetings with interested landholders are to be regularly carried out. Further, it is very important to educated people about how the plant looks like and the hazards associated with it. Education to students as well as workers from construction companies who may work with contaminated machinery around is also very important. Most important is to pass on the current knowledge obtained through research carried out on the weed to the youth in order to educate them for managing the area in future.
i) Manual method
Removing parthenium plants by hand has been employed for the past several years but with disappointing results. In small areas and isolated pockets such as flower beds, lawns, kitchen garden and in intensively cultivated agricultural fields, hand weeding can be really effective and should be preferred. The plants should be uprooted (not cut or broken) before flowering and burnt or composted. If uprooting is done after the flowering stage, the pulled out plants are to be burnt without transporting to far off places, to avoid seed dispersal. Manual method also finds a place in the integrated approach in order to achieve quick results. When biocontrol methods are adopted, there will always be certain proportion of plants left unchecked which is typical of any biocontrol method. Physically removal of such remnants (left out plants) will supplement the biocontrol efforts in checking the growth of parthenium to a satisfactory level. But manual method is neither economical nor practicable in vast areas with heavy infestation. In limited situations the method can work, that too by engaging persons insensitive to parthenium allergy to uproot the plants. Even in such cases, with safety measures such as wearing of hand gloves and nose covers are necessary. However, it should be noted that the relief expected from this method alone is only temporary and needs to be repeated as and when the weed appears.
ii) Chemical Method
Several selective herbicides, soap water and salt water have been tried in experimental plots and subsequently under actual parthenium infested field conditions. Chemicals like 2,4-D sodium salt arsenate compounds, paraquat, bromacil, glyphosate or sodium chloride in recommended dose kill the standing parthenium populations and to some extent suppress immediate germination of the seeds deposited in the soil. In cropped areas, herbicides have been recommended in different crops to control parthenium in respective crops. Here, care needs to be taken to avoid spray drift reaching adjoining sensitive crops.
80% sodium salt of 2,4-D at 5.0Kg a.i./ha as post-emergent spray gave complete control of parthenium at all stages of its growth within a period of 20 days after spray. In Karnataka (India), the following spray schedule has been recommended in non-cropped areas.
a) Young parthenium seedling before flowering should be sprayed with 2,4-D sodium salt@5Kg/ha or MCPA@5Kg/ha of MSMA@5 litre/ha in 1000 litres of water.
b) For grown up parthenium plants, spray 2,4-D sodium salt @ 2.5 kg.+MSMA @ 5 litres/ha or 2,4-D acinal @ 7.5 kg/ha+teepol @ 2.5 litres/ha or urea @ 5 kg/har or MSMA @ 20 litres/ha in 1000 litres of water.
Herbicidal effect of chemicals does not last long; it ends with only one germination. Some times the plants so suppressed by chemicals have regenerated after remaining dormant for a few days. Thus killing of established plants clear the way early only for the next flushes of parthenium plants to emerge. Also chemical treatment repeatedly can kill the existing plants but cannot prevent the entry of seeds getting deposited from outside. The remnant seeds found in several thousands per every square meter of the invaded land as well as newly deposited seeds are always ready for germination with a slight moisture becoming available to them in the soil medium. Because of continuous seed production without any interval in the entire calendar year, reinvasion of the areas can hardly be avoided unless the seed source itself is checked. Since parthenium is more a waste land weed, there will be hardly anybody to invest on chemical treatment just for temporary relief. Even in the agricultural production the chemicals are found expensive and not within the reach of an average farmer. Further, repeated applications either of common salt, soap water or any herbicide with affect other beneficial plants, besides changing soil characters and polluting the environment due to cumulative residual effects. Even handling of chemicals needs expertise, training of skilled workers and adequate caution throughout the process of treatment. Hence, chemical method can not be relied upon even for a reasonable period of freedom from parthenium. Nevertheless, there may arise situations where the vast stretches of already invaded parthenium plots require to be relieved of it immediately for emergencies wherein chemical control method only with have to be resorted to with the knowledge that it gives only temporary control and does not ensure a longer parthenium free period. Further, in the integrated approach also, at the time of sowing and initial establishment of Cassia sericea and other plant enemies and one or two selective herbicide sprays would speed up the process of parthenium replacement.
iii) Biological method
Biological control is the use of living organisms to control pests on animals or plants. A natural enemy such as parasite or predator or disease causing organism is introduced into the environment of pests or if already present is encouraged to become more effective in maintaining the number of pest organisms below the level of economic damage to crops or danger to human health. Of the several methods of pest control in crop production as well as in the living environment, biological approach is considered to be relatively less expensive and free from harmful side effects to the environment and the organisms habituated in the natural course. Insect pests, undesirable plants and many diseases were successfully controlled biologically in the past.
However, parthenium control through biological agents cannot be as simple as in other successful cases because, parthenium is a hardy plant with exceptional adaptability to a wide range of ecosystems. The successful cases are the only ones involving the host organism having very specific adaptability. Use of more than one agent in an integrated approach is essential in suppressing this obnoxious weed. The research on the biological control has revealed that at this point, there are both plant and insect enemies that can contain the growth of this weed. Use of biological agents such as virus and mycoplasma like organisms is still in the experimental stage. Eight species of exotic insects have been introduced into Australia for the biological control of parthenium weed, of which four are established but only one, the moth Epiblem strenuana, is exerting significant control on the weed.
The use of plant and insect enemies is described below:
a) Botanical agents
There are two approaches in using plant enemies in the control of parthenium. One is maintenance of naturally occurring biodiversity and the other is planting selected plant species in target areas.
Maintenance of natural biodiversity
Protecting the naturally existing flora forms is one of the three biocontrol aspects suggested in the Integrated Parthenium Management. A botanical survey in relation to parthenium control across the country has revealed an interesting factor that the parthenium can not penetrate into areas where the natural flora have not been disturbed. Wherever there is indiscriminate destruction of naturally existing plant species, the chances of parthenium proliferation are more. For instance, in areas around cities and urban pockets like Hubli city (Karnataka) where most of the waste land plant species were destroyed in the process of clearing parthenium, parthenium continued to perpetuate, whereas in Dharwad city where no such parthenium control measures were undertaken, parthenium density is very less, because, Cassia sericea, Cassia tora and other waste land species have been preventing the entry and spread of parthenium as can be seen even today.
In Maharashtra, Stylosanthes scabra Vogen has been found to compete with parthenium though allelopathic effect. This has been confirmed by the field observation made by the Officers of the Department of Forests, Karnataka.
An experiment carried out in the University of Agricultural Sciences, Bangalore has revealed that parthenium seeds when sown on (i) barren (vegetation cleared) land and (ii) vegetation covered lands, established to the extent of 100 per cent in the former and only to the extent of 13.8% in the latter. Several other plant species were also identified as having similar impact but with varying degrees. The strongest ones among the so listed species in the order are (i) Cassia sericea (ii) Tephrosia purpurea (iii) Stylosanthes scabra (iv) Croton sparsifiorus (v) Hyptis spp. (vi) Cassia tora (vii) Amaranthus spinosus. The author has observed higher intensity of parthenium in residential and industrial areas but almost zero in lands away from such areas. Further, parthenium growth is very intensive in places where new constructions (like extensions in cities and towns) are going o. All these observations lead to the conclusion that maintenance of biodiversity, that is natural flora wherever possible, is important to check parthenium entry/invasion and its growth as weed.
Parthenium and Cassia
During the visit to Dharwad in October 1982 and 1983, the author observed in and around the city that Cassia sp. was gradually replacing parthenium plants in small pockets. During 1983, replacement of parthenium by Cassia sp. had taken place to a larger extent compared to the previous year. Since the observation was of much interest, the observed Cassia species was got identified as C. sericea (Synonym : uniflora) and a research project proposed was approved by the University of Agricultural Sciences, Bangalore forming a team for studying different aspects in the subject parthenium control. It was further discovered that the new waste land weed Cassia sericea which is a native of Latin America, entered India on its own in late seventies and started colonizing here and there in Dharwad, Bijapur and Belgaum districts gradually replacing parthenium. By 1988, it could spread to other parts of these districts substantially suppressing parthenium growth, Besides, as observed by the author during 1991, it has started spreading to the neighbouring districts like Chitradurga, Shimoga, Raichur, mostly on its own and partially through the efforts of local voluntary workers sowing Cassia sericea seeds with the intention of suppressing parthenium growth.
Further, research at the University of Agricultural Sciences, Bangalore, confirmed that the plant Cassia sericea could exert allelopathic impact by hindering seed germination, and suppressing growth of parthenium both in green house and natural habitat. It was further revealed that the leachates from leaves, pod walls and seeds were more effective than roots in causing such inhibitions. The plant leachates of Cassia sericea have "kolines" (compound of plant origin affecting germination and growth of other plant species) which accumulate in the soil consequent to death of the plant and interfere with germination and growth (mechanism is termed as "Interference") of only parthenium.
The visual observations on growth of these two plants (Parthenium and CS) over three consecutive seasons revealed that there was a gradual decrease in parthenium population and increase in C. sericea population in the three locations experimented. Even the vigour of the parthenium plants growing amidst C. sericea colonies was much low being slender and weak with reduced number of heads. Further, as observed in plants growing in three locations during 1989 rainy season, the parthenium plants growing amidst C. sericea colonies weighed (both fresh and dry) as low as half or even less as compared to those growing in places where there was no influence of C. sericea plants as can be seen from The reduced vigour also reflected in the number of heads per plant which was about half the normal number. In one location where parthenium plants were pulled out in the first year of study, parthenium population was reduced in number much faster, showing a ratio of 1:15, 1:33 and 1:150. In other two locations the reduction of parthenium population followed a different trend, being comparatively low. From this, it may be concluded that the CS plant is capable of replacing parthenium gradually over years and the replacement can be faster if parthenium plants are pulled out in the initial stages of competition.
The scientists of the University of Agricultural Sciences, Bangalore and the voluntary organizations like PROPEL (Programme for Parthenium Elimination) individually and jointly studied this method under field conditions and found promising results in many parts of Bangalore (SKF, Hosakote road, Sarakki layout, Jakkasandra, Thindlu village, Hebbal railway station, Domlur, Koramangala etc.) and also in Tumkur and Mysore districts. Cassia sericea, if established initially by sowing its seeds at the start of rainy season and uprooting and destroying of parthenium before and after sowing, can suppress parthenium faster and substantially and perpetuate on its own in subsequent years.
Promoting growth of CS in abandoned and non-agricultural lands in parthenium infested orchards would be rewarding and should be preferred for the following reasons. It has in its system allelopathic compounds suppressing germination and growth of only parthenium and not other plants and agricultural crops. It has other economic importance such as utility of green plant as (a) soil cover (to prevent erosion), (b) green manure and (c) centering material in civil constructions, dry plant as fuel and seeds as raw material for gum production. Unlike parthenium, CS does not have any adverse effects on human beings, livestock and plant species other than parthenium. As per the work carried out (unpublished) at the University of Agricultural Sciences, Bangalore, the CS leaves contain 22-28% crude protein and 3.5 to 6.5% fat on dry weight basis. This is comparable to the chemical constituents of Cassia tora, a sister species of Cassia sericea Therefore, there is a possibility that the latter can also be substituted in pelleting fish feeds by mixing it at 25% without affecting the quality of the feed i.e., about 17&. This of course needs to be confirmed through experiments.
In case the CS growth is undesirable, it can be easily eradicated since the seeds are heavy and are disseminated through agents that can be controlled and also the seedlings can be identified in the initial stages and uprooted. However, such a situation may not arise, since the plant is harmless from all angles.
Limitations of planting Cassia sericea
Although Cassia sericea is growing on its own replacing parthenium, the process in the natural course is slow. It has taken about 10 years to cover sparsely about five districts in North Kamataka. Further, the CS finds it difficult to establish in very dry areas and also in elevated places, where the soil moisture retentivity is poor. If the species is grown in a particular area, the leachate accumulated from the plants exert allelopathic impact and suppress the germination and growth of parthenium. By chance, if the soils where the leachates have accumulated are removed, there will not be any effect of Cassia sericea. Therefore, the parthenium will start growing. This beneficial plant can not be established amidst lawns and flower beds since it is an annual plant and dries after the completion of its growth and gives a bad appearance thereafter till a fresh growth occurs. It takes time to establish in the initial one or two years which discourages the organizations expecting quick results in controlling parthenium. There is further delay if the seed dormancy is not broken when sowings are taken up in a fresh area.
There are a good number of insect and non-insect pests controlled through biocontrol approach. Control of Opuntia in India through the introduction of Cochineal insect from Australia is a successful instance in India.
In 1978, in Australia, the Commonwealth Institute of Biological Control was contacted by the Queensland Department of Lands to carry out a 3 year study on insects attacking Parthenium hysterophous in Mexico. One of the insects from Mexico, a leaf-feeding chrysomelid, Zygogramma sp. nr. malvae Stal, was shown to be host-specific. A second species, the seed-weevil, Smicrony Iutulentus Dietz also proved host specific in preliminary testing (McClay, 1980) and in December 1979, it was introduced in Queensland. The weed is under control in Australia.
Insects feeding on parthenium
Many insects are observed to feed on parthenium. Some of them as reported form different places are mentioned below.
Limitations of using the beetle
c) Virus and MLOs
Some scientists have held the view that there may be few viruses that can be used in biocontrol of parthenium. Parthenium phyllody disease is very common on parthenium weed in India. The incidence varies from 10 (February-June) to 100% (August-December). The leafhopper (Orosius albicinctus) population in the field is positively correlated with the incidence of this disease. The phyllody disease of parthenium is transmitted by O. albicinctus and the active transmission is found to be 55%. The minimum acquisition access period is found to be 20 minutes and the inoculation access period is 15 minutes. Incubation period in the vector varies from 15 to 20 days. The pathogen persists throughout the life of the O. albicinctus. Parthenium phyllody was transmitted by O. albicinctus to aster, cowpea, blackgram, greengram, horsegram, Limabean, redgram, sunhemp, fieldbean, soybean and wingedbean. Mycoplasma diseases occurring naturally on these crop plants were transmitted to parthenium by O. albicinctus. Scientists researching on this area feel that there is no hope of using this as a biocontrol method in the near future, but their efforts continue work with the hope of positive results in future.
iv) Other methods
Some scientists have advocated two more methods viz., cultural practice and growing competitive crops. These are impracticable for the following reasons. Operations such as ploughing, passing of cultivator/harrow and interculture cannot be practiced in the lands with heavy parthenium infestations which are usually waste lands or no man's lands. Also such operation incur heavy recurring expenditure. The only situation where cultural practice can work is orchards like guave, coconut, mango etc. where usually such operations are done traditionally and all weeds including parthenium are controlled in routine way with scheduled seasonal operations.
Growing competitive crops is also not practicable because parthenium is not such a big problem in cultivated lands where regular weeding operation is done. Further, cropping pattern has to be decided based on the suitability, cropping sequence, crop compatibility and marketability and changing the crop for the sake of parthenium control is not going to become practicable. One possibility of using a plant enemy in intensively cultivated land to control parthenium is only growing of Stylosanthus scabra and Tephrosea spp. in lands exclusively devoted to forage production. Some information of relevance to this aspect can also be found in the section relating to biological control of parthenium through plants.
Dr. M. Mahadevappa, born on August 4, 1937, in Madapur, Chamarajanagar district, Karnataka, India, hails from rural agricultural family. He completed Bachelor degree in Agriculture, Master and Doctorate degree in Genetics and Plant Breeding in succession from 1960. Dr. M. Mahadevappa, as a researcher has been instrumental in releasing nine high yielding rice varieties and has been the architect in developing a Hybrid rice. Sustained efforts made by him over two decades has lead to development of Integrated Parthenium Weed Management (IPWM) strategy, an ecofriendly and sustainable approach.
As a teacher for over 13 years, he has guided 16 Ph. D. and 41 M.Sc. (Agri) students.
The author has served in various capacities in the field of agricultural research and education of 3 decades. He has served as Vice-Chancellor, University of Agricultural Sciences, Dharwad, Karnataka from 1994-2000. He is a Fellow of National Academy of Agricultural Sciences, Member of ICAR governing body and Chairman of Several Research Advisory Committees and Quinquennial Review Team. Currently, he is the President of Association of Indian Agricultural Universities.
Among several awards conferred on him, Rajyotsava Award of the Karnataka Government and the Hooker Award of the Indian Agricultural Research Institute, New Delhi are outstanding ones. He has visited more than 12 countries and presented research papers in National and International Conferences. He has published more than 200 scientific articles in reputed journals and organized two International Conferences. He has a great vision to foresee the future and plan for the development of Science & Technology.
Effect of Parthenium on human health and livestock
(Source : Mahadevappa, M. (1999). Parthenium
and its management. Pbl. Publication Center, University of Agricultural Science, Dharwad -
580 005, India p. 46)
(Source : Mahadevappa, M. (1999). Parthenium and its management. Pbl. Publication Center, University of Agricultural Science, Dharwad - 580 005, India p. 46)