Traditional (past), present, and future approaches to control pesticide residue in fresh produce
Introduction:
The major challenge that agriculture faces in the twenty-first century is the need to give food to the world’s quickly growing population. The selection of a high-yielding variety of crops has greatly helped mankind in reducing poverty and hunger. Reducing crop losses due to pests and diseases has mainly been dealt with by the use of synthetic pesticides. Modern agricultural practices partially indebted its success to the discovery and use of these chemicals. Over the past few decades, on the other hand, concerns have been developed over the environmental consequences and long-term sustainability. Indiscriminate use of synthetic pesticides has given rise to a number of problems, including the extensive development of resistance to pesticides, issues of pesticide residues, non-target activity, environmental pollution, and public concerns about the possible health risks.
The above information demands the need for safer, environmentally friendly management practices which, if possible, also be exhibiting new biochemical modes of action to reduce the development of pesticide resistance. Therefore, natural compounds have increasingly become the focal point among those who were interested in unearthing sustainable crop protection strategies. This paper focuses initially on the traditional and then on the present crop protection strategies followed by farmers in cultivation. It discusses the perspectives and challenges of sustainable alternatives in pest management approaches. The sustainable and ecofriendly management practices selected from the past as well as the present scenario has to be improved and refined further in the future along with new management strategies too. The present scenario demands the urge for developing innovative future strategies in crop protection with low residue problems and higher safety.
Traditional (past) approaches
There are four schools of thought to control pesticide residue according to Peshin and Zhang (2014). These include pesticide-free management, integrated management (IM), Integrated Management with chemical control as last measure, and the development of transgenic crops. The traditional crop protection strategies were more associated with the first school of thought i.e., pesticide-free management.
Traditional crop protection strategies
According to an African Proverb “When a knowledgeable old person dies, a whole library disappears.” Human communities have always generated, refined, and passed on knowledge from generation to generation. Traditional methods form basis of management of plant diseases in low input situations. The ancient Indian literature documents the use of plant products, animal products, and wastes for curing the diseases of human beings and plants. Early references to plant protection are found in the following literature:
- Vedas - Atharvaveda (c.1000 BC)
- Kautilya’s Arthashastra (c.300 BC)
- Krishi Parashara (c.400 BC)
- Brihat Samhita of Varahamira (c.600 AD)
- Surapala’s Vrikshayurveda (c.1000AD)
- Lokopakara by Chavundaraya (c.1108 AD)
- Sarangadhara’s Upavanavinoda (c.1300 AD)
- Viswavallabh of Chakrapani Mishra (c.1577AD)
Among these, Surapala’s Vrikshayurveda elaborates plant protection practices in a very systemic manner. He has mentioned from seed treatment to storage of grains. Traditional methods of plant protection are well explained in it including disease avoidance, seed treatment, and disease treatment.
Identified Indigenous Technical Knowledge in crop protection
Fresh cow dung suspension is sprayed to control the Bacterial Leave Blight (BLB). The cow dung suspension will have enormous amount of bacteriophages (bacteria scavenger viruses). The crop is even protected from cattle because they do not like to graze on cow-dung-treated crops. Another technique is the Application of suspension of neem leaves and grinded neem seeds with soap or surf and raw turmeric. The suspension produces a disagreeable odor and reduces the chances of occurrence of diseases (fungal and bacterial) wherein it acts as a precautionary measure.
Some of the local practices adopted in past for crop protection include planting across the wind direction to overcome the problem of some airborne disease, Tieing of areca nut seedlings with coconut and areca nut fronds to protect them from western sun scorching, Pasting of lime on areca trees to avoid ill effect due to sun scorching, Kotte tying for areca bunches to overcome problem of koleroga (fruit rot) of areca nut and watering of nursery beds during early morning for higher seedlings vigour and stand particularly followed in chilli and brinjal. Mixed cropping is practiced in Jowar with tur to prevent movement of mites which transmits sterility mosaic, a viral disease of pigeon pea. Moreover, it also helps to minimize the tur wilt.
For managing soil-borne pathogens including Pythium, Phytophthora, etc. several management practices were adopted which include burning nursery with leaf litter and farm waste, collection and burning of stubbles in the field, preparation of raised beds, fields, and ridges ('Chinampas / floating garden'), earthing up to overcome Pythium damping off in nursery in brinjal and tomato, flooding with water to overcome the problem of soil-borne pathogens by creating anaerobic conditions. eg: Fusarium oxysporum fsp. cubense causing Panama disease of banana, fallowing which is generally more effective in combination with rotations and summer plowing exposes the survival structures to hot sun and destroy them thereby reducing the problem of nematode infestation and soil-borne pathogens.
ITKs
- Diseases managed
- Cow dung suspension
- Bacterial Leaf Blight in rice
- Suspension of neem leaves and grinded seed with soap / surf & raw turmeric
- Fungal & bacterial diseases
- Dusting wood ashes
- Brown-spot disease in rice
- Shade regulation
- Coffee leaf rust & blister blight of tea
- Planting across wind direction
- Airborne disease
- Kotte tying for aareca nutches
- Rotting of arecanut
- Salt water treatment
- Seed-borne diseases
- Earthing up
- Pythium damping off
- Flooding with water
- Soil borne pathogens, nematodes
- Crop rotation
- Fallowing, Mulching
- Summer plowing
Application of organic amendments
In addition, organic amendments like oilcake were applied liberally in different crops to manage soil-borne diseases. It enhances the soil temperature and kill pathogens but enhances the population of beneficial organisms by serving as source of nutrients. Mulching is also done with green manure in paddy to overcome the problem of soil-borne disease. For example, Chromolaena odorata was used as mulching material to manage soft rot, bacterial wilt, and Fusarium dry rot in Ginger.
Organic preparations like Panchagavya, Dashagavya, etc were used in crop protection and crop production since time immemorial. In general, it provides nutrients to plants and resistance to diseases and pests. Panchagavya: ‘Panch’ means five and ‘gavya’ means related to cow- in Hindi. It is a preparation made out of five products of cow including – milk, ghee, curd, dung, and urine along with 4 other products like jaggery, banana, Tender coconut, and water. Used as source of nutrients as well as for crop protection. It is used even today. The rate of application is 5%. Dashagavya: ‘Dasha’ means Ten and ‘gavya’ – cow. It is yet another preparation with panchagavya and extracts of 9 plants having therapeutic and nutraceutical properties (IARD 6020 filed trip in Kerala).
Traditional crop protection measures have an important place for the use of botanicals. This includes use of botanicals like tulsi, onion, ginger, chromolaena, etc for crop protection. Tulsi was and still used in some preparations to control blast of rice and insects in sapota and guava. Onion was used for pest and disease control in maize and sugarcane. Similarly ginger is also having effect against pathogens as well as pests. It is used against some viral and bacterial diseases. The preparation of ginger in the cows' urine was used to spray in tomato against Tomato mosaic.
In addition to these botanicals, salt, milk, etc also have beneficial effects on crops. Salt sprays helped to control wilt in Pigeon pea. It was also used against Khaira disease in Paddy. A diluted solution (10 times) of fermented cow’s urine was used against bacterial wilt in tomato, potato, and chilies (Ralstonia solanacearum). Turmeric powder (100 gm) in indigenous cow urine (1.5 L) and water (100 L) is used to manage powdery mildew in vegetables and fruit crops.
The dissemination of ITK has faced many constraints. It has to be passed orally and held in the heads of practitioner. There is a non-availability of material input, and non-availability of labor and the ITK's are usually known to uneducated, aged people in villages. Moreover, it is found in remote villages and tribal tracts. There is a need for awareness creation. Travelling to remote places, staying there, documenting the details, and publication require funds. Translation from local language into English and other regional languages is needed, which is a tedious process. Traditional practices have been developed through practical experience of the local population of the particular region. The methods have been designed with great ingenuity.
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Since, ITKs are eco-friendly and organic in nature, so proper documentation, scientific validation, and refinement with modern technical knowledge is essential to conserve this knowledge and use effectively for sustainable crop cultivation. ITKs are cheap, easy to adopt, locally available, and reduce the input of chemical pesticides in our food chain and the environment.
Introduction of Pesticides In Crop Protection
The terminology originated from two ‘Latin’ words namely ‘pestis’ meaning plague or pest and ‘caedo’ means to kill. In agriculture, it means any chemicals that are used to eliminate organisms which are harmful and undesirable in field conditions as well as during the storage of crops or agricultural produces.
History of pesticide use
The oldest and most differentiated group of plant protection chemicals are insecticides. The application of insecticides can be even traced in the very distant past. First record documented dates back to 2500 BC where in the Sumerians used Sulphur compounds against insects by rubbing it on the skin. Even in 1200 BC, the Chinese used lime, sawdust, etc., and insecticides of plant origin to ward off pests especially the storage pests from seeds.
Pesticides in Agriculture- Pre-Green Revolution
Till 1940s inorganic substances like sodium chlorate, sulphuric acid, organic chemicals derived from natural sources were used extensively in pest management strategies. Some of the pesticides were derived out of the by-products of coal gas production and other industrial processes. The organ chemicals such as nitrophenols, naphthalene, chlorophenols and petroleum oils were then used for fungal as well as insect pests management, at the same time the chemicals such as sodium arsenate, ammonium sulphate, etc.were used against weeds asherbicides. The main drawback of these chemicals were the high rates of application, lack of proper selectivity and phytotoxicity to host plants.
The use and manufacturing of synthetic pesticides accelerated during 1940s. Many efficient pesticides appeared during this period including captan, DDT, BHC, aldrin, dieldrin, endrin, chlordane, parathion, and 2,4-D. These products were effective and at the same time inexpensive also, with DDT being the most popular chemical owing to its broad spectrum of activity (K.S. Delaplane, 2000). The insecticidal properties of DDT was invented by Paul Muller in 1939. DDT initially appeared to be low in toxicity to mammals and reduced pests and insect-borne diseases. Synthetic pesticides began to develop after this period. In 1946 first case of resistance to DDT was reported in house flies (Ankersmit GW, 1953). The indiscriminate use of pesticides leads to the pesticide residue problem which in-turn resulted in harm to nontarget plants and animals. Even though the use of synthetic organ chemical pesticides helped in reduction of pest and disease incidence it also paved the route for serious issues like pesticide resistance, pest resurgence, and pesticide residue problems.
A glance into the past provides numerous examples of the adverse impact of human activities conducted in injudicious or rude manner became a danger to human survival in a short span.
Pesticides in Agriculture - Post Green Revolution
Till the end of 1950s, the consumers, as well as the policymakers, were not very anxious about the possible health risks (Bill Ganzel, 2007). The concern has budded when some cases of harm from misuse of the chemicals aroused. But comparatively the new pesticides in the market seemed rather safe, particularly compared to the metallic insecticides like arsenic which killed many people in 1920s and 1930s. Nevertheless, the problems can take place due to the unsystematic and indiscriminate use. Pesticide use increased nationally as well as globally during 1960s (CropLife Canada, 2002).
Green revolution commenced in the early 1960s. Modern technology and agricultural practices gradually replaced the traditional agricultural practices followed in India. The Green Revolution was initiated in India to raise the food production and supply food to the millions of half-starved people all over the nation. Although the dependence on chemicals in Green Revolution agriculture has contributed to the incredible gains in the food grains production in the world, particularly in developing countries, the widespread use of fertilizers and pesticides has caused severe public health and environmental problems (Pimentel, 1996; WRI, 1992).
In 1962, Rachel Carson in her book ‘Silent Spring’ addressed the problems linked to the indiscriminate use of pesticides and lined the way for safer and more environment-friendly pesticides (Rachel Carson,1962). Research in developing safer pesticides continued and in 1970s and 1980s new pesticides were introduced in the market. In the class of Herbicides, glyphosate, sulfonylurea, imidazolinone, dinitroanilines, aryloxyphenoxy propionate, and cyclohexane- diones families were the new introduction. In the case of Insecticides synthesis of a 3rd generation of pyrethroids, avermectins, benzoylureas and Bt (Bacillus thuringiensis) took place. Fungicides like triazole, morpholine, imidazole, pyrimidine, and dicarboxamide families also made their appearance in this period. Agrochemicals introduced at this time had peculiarities like single mode of action, more selectivity, and less resistance to pesticides (Smith and Secoy,1976).
The researches in pesticides during 1990s concentrated more on finding new chemicals with better selectivity and improved environmental and toxicological status. The then released chemicals include triazolopyrimidine, triketone isoxazole, etc. in the category of herbicides, fungicides including strobilurins, azolone, etc., and insectides like chloronicotinyl, spinosyn, fiprole, and diacylhydrazin. The highlighted feature of these chemicals was the low rate of application (used at grams rather than a kg per hectare). Hence this period showcased the introduction of newer, more user-friendly, and environmentally safe formulations (Abhilash and Singh,2009).
Integrated pest management systems, which make use of all accessible and available pest management measures in order to discourage the increase of pest populations and reduce the use of pesticides to levels that are safer and economically acceptable, have also contributed to dropping pesticide use. There is growing public worry that no one is aware of the extent of pesticide contamination on local, fresh produces like fruits and vegetables purchased daily which may lead to possible, lasting, undesirable health effects on consumers.
Positive Impacts of Green Revolution
The benefits of green revolution includes increase in agricultural production, economic upliftment of farmers, Import of food grains reduced, generation of rural employment, capitalistic farming, and Growth of industries. Along with these benefits, there are obvious and at times hidden issues which show the negative side of the green revolution.
Toxic Consequences of the Green Revolution in India
The benefits of the Green Revolution were attached with unexpected detrimental consequences from chemical pollution. The rise in bad health along with other ailments such as renal failure, stillborn babies, and birth defects are attributed to the overuse and exploitation of pesticides. In several cases, rural farmers were unaware of the proper usage, handling, and disposal methods, without using protective outfits or equipment when using extremely toxic chemicals. In some cases, even the pesticide containers are sometimes reused as household containers. The majority of the farmers think that applying more pesticides and herbicides is better, without understanding the fact that the heavy use is progressively poisoning the soil and water supplies (Pimentel, 1996).
Prof. R. K. Mahajan, an agricultural economist at Punjabi University once quoted that “The Green Revolution is not as green as it was earlier; it has now become brown and pale”. Pesticides used during the cultivation often lead to the occurrence of pesticide residues in fruits and vegetables even after harvest. The presence of pesticide residues on fresh produce is a distress for consumers.
Conclusion
Today the pest management toolbox has expanded to include use of genetically engineered crops designed to produce their own insecticides or exhibit resistance. These include herbicide tolerant crops like soybeans, corn, canola, and cotton and varieties of corn and cotton resistant to corn borer and bollworm. In addition, the use of Integrated Management (IM) systems and biological control discouraged the development of pest populations and reduce the use of pesticides. Combining the best of traditional agricultural methods with the best of modern agriculture should go a long way toward sustaining agriculture (Thurston, 1990).
References
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