Selective herbicides are used for weed control where crops are unaffected but weeds are wiped out. A chemical that is maize-selective, for example, would destroy all other weeds except the grass family, which maize belongs. Maize-like grasses would also be spared in this case. Non-selective herbicides wipe off both crops and weeds.
Pre-emergence herbicides are sprayed after land preparation and planting but before the seeds and weeds germinate. Some pre-emergence herbicides are sprayed on prepared land before the seeds or crops are planted or transplanted to retard emergence of weeds. Post-emergence herbicides, on the other hand, is applied after the weeds and seeds/plants have emerged. Selective post-emergence herbicides will, therefore, leave the seedlings or crops undamaged, while the weeds would be wiped out.
However, there have been concerns over deposits of chemicals on foods emanating from such a cultivation system and safety of the foods for human consumption. Professor Kolawole Adebayo, an extension specialist and Regional Coordinator of Bill and Melinda Gates Foundation-sponsored Cassava: Adding Value for Africa (C:AVA), while explaining dangers inherent in the indiscriminate use of herbicides, said when used on agricultural farmlands, they have implications for farm productivity and quality of farm products. These implications may be positive or negative.He said one of the primary reasons that farmers use herbicides is to reduce cost of weeding and ensure more profitable returns on farm investments.
He pointed out that where herbicides are properly used, following specific instructions and guidelines for safe use, problems to human health and natural ecology are usually contained. “Problems arise,” Prof. Adebayo added, “with misuse of herbicides. Wrong use, use of wrong dosages, non-adherence to prescriptions, among others, make chemicals to become adverse factors in the environment and the food systems.”
Prof. Adebayo also explained that diseases of the internal organs or even tumors of varying dimensions had been attributed to wrong use of herbicides, saying, “Indiscriminate and wrong use also have negative effect on local ecosystems and when these chemicals find their ways into water bodies, the problems tend to permeate downstream.”
Supporting the above, the Managing Director of the Lower Niger River Basin Development Authority, Ilorin, in Kwara State, Adeniyi Aremu, said humans who are exposed to herbicides through oral, skin, eye contacts or inhalation are at high risk of respiratory damage, irritation, eye problem, fatigue, vomiting, skin problems, dizziness, cancer, and severe damage to body’s immunity system.
“Herbicides also contaminate surface and ground water through runoff, spills, leakages and leaching,” Aremu added, saying, “In soil ecosystems, herbicides disrupt natural processes within the soil structure by killing some soil micro flora, altering biochemical processes and reducing microbial activities.”
Mr David Ayodele, an agribusiness consultant and land preparation specialist based in Ilorin, Kwara State, said the effect of herbicides on ecosystems and human health could not be overemphasized, especially in regions where there is less education and technical competence in handling them. Ayodele, like Aremu, said poor handling and use of herbicides could lead to ill health, contamination of water bodies and undue accumulation of salts in the soil. Farmers need to be properly trained on safe handling and appropriate application of herbicides to avoid misuse and death, he added.
“For example,” Ayodele said, “there are four major routes through which herbicides reach usable water. It may drift outside of the intended area when it is sprayed; it may percolate, or leach through the soil; it may be carried to the water as runoff, or it may be spilled accidentally or through neglect caused by poor knowledge of use and handling.”
Another agricultural specialist, Dr Akin Oloniruha, a former provost of the Federal College of Agriculture, Kabba, Kogi State, said there is no way one would release chemicals like herbicides on farmlands without negative effects on the ecosystem. “Safety is to ensure that herbicides are used according to specifications on the labels and adhere to safety standards. But unfortunately for us in this country, there is no agency regulating the use of herbicides. Even the workers using them are unaware that they need to put on protective coverings while using herbicides. Some of them are toxic to the skin, eyes, the respiratory system and the nervous system,” he said.
Oloniruha explained that the “residues of the chemicals end up in our underground and surface waters with deleterious consequences for human health and aquatic life, saying, “herbicides that are strictly for farm use are now used to control weeds in domestic areas where we have wells and boreholes servicing humans and livestock. In such cases, the chemicals will end up in our waters.”
He added that as the case with herbicides, people hardly use protective coverings while using pesticides. Some friendly insects like pollinators and other organisms also get destroyed by pesticides, he lamented, saying, “in Nigeria where there is apparently no one responsible for food safety (except packaged foods), there are heavy loads of pesticide residues in our farm produce. This explains why most of our farm produce cannot meet market standards in European and American markets.”He said most countries now adopt integrated pest control with less emphases on chemical control.
Dr Olugbenga Adeoluwa, the Vice-President of the Association of Organic Agriculture Practitioners of Nigeria (AOAPN) and the National Project Coordinator of the Ecological Organic Agriculture Initiative (EOAI) in Nigeria, said in an interview with The Guardian recently that organic agriculture was the answer to many challenges associated with synthetic agriculture.
Dispelling misconceptions about organic agriculture, AdeOluwa said, “It does not mean you cannot use fertiliser, high-yielding varieties or insecticides. What organic agriculture promotes is that, should it happen that you have to use these, you have to use organic fertiliser, pesticides, and improved seeds that have been done in natural ways.”
Source: The Guardian