Weeds

Paraquat has been an essential tool for farmers in protecting sustainable cropping systems for more than 50 years. Its unique properties have enabled the development of vital new crop production techniques, especially no-till.
This section includes in-depth features that cover topics including:
Paraquat's role in sustainable agriculture
All about weeds and weed control
Important crops and their production systems
Paraquat led to a revolution in land preparation that has had profound economic, social and agronomic effects around the world.
The herbicidal properties of paraquat were discovered by ICI (a legacy company of Syngenta) in 1955 and was introduced to world markets in 1962 under the brand name GRAMOXONE®. Paraquat quickly gained acceptance as a tool for controlling weeds in emerged row crops and tree crops. However, it was the realization that paraquat could replace time- and labor-intensive plowing, which in the 1960s and 1970s led to an expansion of research around the world on a scale unprecedented for a single agricultural chemical and to a revolution in farming.
Why is paraquat such an unique product and why is it so valuable to farmers? Before we can answer that we have to consider the importance of weeds.
Weeds have existed as long as man has farmed. Weeds hinder planting a crop and once the crop has emerged they continue to compete for water, light, nutrients and space. Weeds need to be removed before planting and controlled thereafter.   There are several ways to control weeds:
Hand Weeding is hard, debilitating and tedious work. It can occupy the farmer and his family for many hours of the day.  In many parts of the world hand weeding is the most time-consuming human activity aside from sleeping.
Mode of Action
Paraquat acts in the presence of light to desiccate the green parts of all plants with which it comes into contact. After application, penetration through the leaf surface occurs almost immediately. This absorption is increased by high light intensity and humidity and by added non-ionic adjuvant in the formulation which ensure good spray retention and wetting of target foliage.
The site of action for paraquat is in the chloroplast. The chloroplasts contain the photosynthetic systems of green plants, which absorb light energy that is used to produce sugars. Paraquat is known to act on the photosynthetic membrane system called photosystem I, which produces free electrons to drive photosynthesis.
The free electrons from photosystem I react with the paraquat ion to give the free radical form. Oxygen rapidly reconverts this free radical and in that process produces super oxides. Chemically highly reactive, super oxides attack unsaturated membrane fatty acids, rapidly opening up and disintegrating the cell membranes and tissues. The paraquat ion/free radical process then recycles producing further quantities of super oxide until the supply of free electrons ceases.
Controls weeds
Paraquat is an important tool for weed management. It controls many species and can be used with most crops. Its mode of action means that it is especially valuable where intensive use of glyphosate has caused, or threatens to cause, the development of glyphosate resistant weeds.
Case Study
The extensive adoption of glyphosate tolerant GM crops has led to farmers over-relying on glyphosate.
Although glyphosate is encouraging the continued adoption of no-till, with all the benefits to soil conservation that brings, up to three million hectares in Brazil are now estimated to be infested with glyphosate resistant weeds.
However, an integrated weed control system involves continuing to spray glyphosate for burndown, but following just before or just after planting the crop with an application of a paraquat-based herbicide.
Read more …
 
 
Acts fast
Paraquat acts fast in all seasons, no matter what the conditions: hot, dry, wet, early season or late. Paraquat is rainfast in 15 - 30 minutes.
Case Study
In West Bengal, India, using paraquat to burndown weeds in a no-till system means farmers can transplant a new rice crop after only four days compared to the usual 12 days. Traditionally, fields are plowed and farmers have to wait for buried weeds to decompose sufficiently to allow a final cultivation.
Articles in this section are about specific examples of how paraquat is being used and new uses explored in sustainable cropping systems.
The case studies show how farmers, their families and their land can benefit by farming with paraquat; and how this enables them to grow better crops.
Use
Paraquat is one of the most widely used herbicides in the world, marketed globally under the brand name Gramoxone by Syngenta. A list of other brand names under which paraquat is sold can be found here.
Paraquat is used in nearly 90 countries either to prepare the land for planting or for controlling weeds in more than 100 crops, including major food crops: corn, rice, soya, wheat, potatoes; major fruits: apples, oranges, bananas; beverages: coffee, tea, cocoa; and processed crops: cotton, oil palm, sugarcane, and rubber.
In this section you can find information about crops for which paraquat is an essential production tool and a selection of case studies illustrating the benefits from using paraquat in some very different cropping systems.
The crop reviews describe the crop, where it is grown and what it is used for; crop production methods and weed, insect pest and disease problems; and the key benefits from using paraquat. They are summarised here and more extensive articles can be found in the Knowledge Bank.
The case studies demonstrate why paraquat is an essential tool for use in sustainable agriculture, and one which many farmers around the world rely upon for their livelihoods and to support their families.

Paraquat has been a valuable tool for farmers all over the world for nearly 50 years. Its speed of action, rainfastness and now its role as a weed resistance fighter are unsurpassed.
However, paraquat’s importance and benefits go beyond simply weed control. Its unique property of being locked onto soil so tightly on contact, and the consequent biological inactivation, mean that it has become a key component in conservation tillage systems, especially no-till.
Paraquat plus reduced tillage improves soil structure and fertility, timeliness of operations, biodiversity and the overall profitability of farming. It is also unique as a non-selective herbicide in being able to be sprayed between the rows of growing crops without fear of crop damage.
In this section you can find out about the specific benefits paraquat brings on the farm, for the environment and in rural communities.
 
Key benefits of paraquat
On the farm For the environment In rural communities Controls weeds
Reduces [no-glossary] soil erosion
Creates opportunities
Acts fast
Increases soil organic matter
What is Paraquat?
Paraquat is a herbicide (chemical weed killer) used to control a very broad range of weeds (unwanted plants) in more than 100 crops, including cereals, oilseeds, fruit and vegetables, growing in all climates. Weeds shade crops, take their water and nutrients, and make harvesting difficult. The leading manufacturer of paraquat is Syngenta, which (as ICI) developed the active ingredient (AI) in the early 1960’s. Since then, paraquat has made possible many innovations in sustainable farming systems, based on its simplification of crop production by effectively controlling weeds and, in doing so, removing the need for ploughing to bury them. This has freed up farmers’ time and also helped care for the soil. Paraquat is one of the most widely used herbicides in the world. It has been approved for use by authorities in nearly 90 countries. When used as recommended, paraquat is effective and safe to users, consumers and the environment.
Key facts about the safe and effective use of paraquat are noted below. This fact sheet also contains a list of referenced scientific papers and other publications and a summary of technical information.
Why Farmers Use Paraquat
Spraying paraquat lets millions of farmers grow better crops more easily, while respecting the environment. Paraquat has a unique set of characteristics: