Fig. Some commonly used glyphosate in India
Glyphosate, a weed killer, was introduced in the market by Monsanto Company during 1970s. It is a leading broad spectrum, non-selective, systemic herbicide for the control of annual and perennial weeds before the emergence of any agronomic crops. It is also used in non-crop and plantation crops. It is marketed under the trade name Roundup. Glyphosate is used against the annual broadleaf weeds and grasses that compete with the crops. When applied, it is absorbed through foliage and minimally through roots which means it is only effective on active growing plants and cannot prevent seeds from germinating. Recommended dose of application rates of glyphosate do not exceed 5.8 kg a.i. ha-1. After its application, it is readily transported around the plant to growing roots and leaves and this systemic activity is important for its effectiveness. Glyphosate has often been termed as a “once-in-a-century herbicide” because of its tremendous impact on weed management and the crop production industry.
Glyphosate is a weak organic acid, named chemically as N-(phosphonomethyl)glycine. It is usually formulated as the isopropylamine or trimethylsulfonium salt of glyphosate.
Advantages
• When applied appropriately, it can promote useful effects. In sugarcane, for example, glyphosate application increases sucrose concentration before harvest.
• In grain crops (wheat, barley, oats), uniformly dried crops do not have to be windrowed (swathed and dried) prior to harvest, but can easily be straight-cut and harvested. This saves the farmer time and money, which is important in northern regions where the growing season is short, and it enhances grain storage when the grain has lower and more uniform moisture content.
• Pure glyphosate is low in toxicity to fish and other wildlife, and it binds tightly to soil so is unlikely to contaminate groundwater.
• Use of glyphosate based herbicides reduces the need for labor-intensive weed control, reduce pest pressure and improve crop quality and yield.
• Use of glyphosate based herbicides reduces the need for conventional tilling thereby reducing carbon dioxide emissions.
• Glyphosate based herbicides have a shorter active life span and safer chemistry than many other herbicides, when used as per product label. It has been reported that glyphosate based herbicides have a typical half-life of only 47 days in soil and are inactive to plant life once they bind to the soil.
Disadvantages
• Glyphosate does not break down rapidly and may leave residue, cause resistance and pollution.
• Glyphosate can control weeds but being non-selective in nature, it can also effectively kill the main crops.
• Several studies have shown that the average of glyphosate application per hectare has shown a marked global increase associated with the appearance of a growing number of tolerant or resistant weeds.
• Glyphosate may be comparatively low in toxicity when judged next to other herbicides, but it is still toxic. Exposure to glyphosate can cause skin irritations, difficulty in swallowing, diarrhea and vomiting.
• Monsanto advertises that glyphosate is not considered a threat to drinking water since it is bound by soil and sediment and is rapidly biodegraded. However, glyphosate has the potential to contaminate the surface water if it is carried by soil particles suspended in runoff water.
Damaging effects on plants
• Because glyphosate is systemic, excess residue levels can persist in plants due to incorrect application and this may render the crop unfit for sale.
• Negative effects on non-target plants are of serious concern among producers. Glyphosate applied to control weeds can reach the non-target areas through several routes. The primary route is through undirected spray applications or “spray drift”, which can directly carry the herbicide chemical to crops. Although herbicide exposure during application drift would be considered sub-lethal, response can be potentially severe for susceptible crops. For instance, drift from glyphosate has been found to cause distorted fruit (often termed as “cat-facing”) to develop in tomatoes at sub-lethal rates of exposure.
• Excessive glyphosate application has been linked to disease development in many crops. For instance, glyphosate applications were found to be the main factor in the development of diseases such as Fusarium head blight in agronomic crops
• Glyphosate can also predispose plants to diseases indirectly by reducing the overall growth and vigor of the plants, modifying soil micro flora that affects the availability of nutrients required for disease resistance, and altering the physiological efficiency of plants.
Damaging effects on animals, insects and organisms
• Monsanto claims that extensive testing of glyphosate has shown that it has a low order of toxicity and exhibits no unusual toxicological effects in animals.
• Experimental research suggests that some important beneficial soil bacteria and fungi, including nitrogen-fixing bacteria and fungi responsible for breaking down organic matter, are affected by glyphosate. It has been also been found to inhibit the mycorrhizal fungi.
• Glyphosate has also been found to adversely affect earthworms, by reduction in growth, increase in maturity time, and increased in mortality.
• Some studies have shown that Roundup treatment reduces the numbers of spiders, and there was the large declined in the population of large carabid beetle species upon the glyphosate treatment.
Damaging effects on humans
• Human skin absorbs glyphosate poorly, and if glyphosate enters the body through the skin or mouth, it passes out of the body through urine or faeces within one day. However, other chemicals included in glyphosate products to aid their sticking, penetration and other effects can cause eye and skin irritation, and irritate the nose and throat if breathed.
• Swallowing a glyphosate product can cause nausea, vomiting and diarrhea, burns to the mouth and throat, and increased saliva. Pets and other animals can be at risk if they touch or eat plants treated with glyphosate products.
• As per it is being carcinogenic, most recently, in January 2020, the U.S. EPA published its Interim registration review decision on glyphosate and stated “EPA has thoroughly evaluated potential human health risk associated with exposure to glyphosate and determined that there are no risks to human health from the current registered uses of glyphosate and that glyphosate is not likely to be carcinogenic to humans”. In addition to the U.S. EPA, the European Food Safety Authority (EFSA), the European Chemicals Agency (ECHA), and the leading health authorities in Germany, Australia, Korea, Canada, New Zealand, Japan, and elsewhere around the world continue to conclude that glyphosate-based products are safe when used as directed and that glyphosate does not pose a carcinogenic risk.
Glyphosate is already the world’s most-used herbicide, and its use has been increasing year after year with the introduction of herbicide tolerant crops. Studies have shown that it has got both the risks and benefits, and in long term the risk might be alarming to both the living being as well as to the environment creating imbalance. So, an alternative approaches to weed management is the need of the hour, to reduced the alarming rate of glyphosate usage.
(Article contributed by Christy BK Sangma, Tolika Swu, Imtisenla Walling and Bendangjungla Pongener Scientist, ICAR-RC-NEHR, Nagaland Centre, Jharnapani, Medziphema)
