Weed resistance

First case of glufosinate resistance recorded

The first weed species to develop resistance to the non-selective herbicide glufosinate has been recorded by researchers in Malaysia.
Preliminary experiments have confirmed concerns that an aggressive grass weed is developing populations which are no longer controlled by glufosinate.
Weed scientists from the University of Malaya have been investigating reports of weed control problems in an oil palm nursery in the state of Pahang. The weed in question is goosegrass (Eleusine indica), a globally important weed of many warm climate crops.
In Malaysia it is a particularly serious problem in oil palm and rubber plantations, and on smallholdings growing fruit and vegetables.
Goosegrass has already developed resistance to several herbicide modes of action (MOA) in a number of countries around the world. It was the second weed species to be recorded as becoming resistant to glyphosate, also in Malaysia1. To keep weed resistance at bay, and avert the threat it poses to food production, it is vital to use integrated weed management practices. These involve using herbicides with different MOA. Like paraquat and glyphosate, glufosinate has a very distinctive MOA.

Paraquat fights glyphosate resistant Palmer amaranth

This season has seen a redoubling of efforts to fight the spread of glyphosate resistant Palmer amaranth (Amaranthus palmeri) in US crops. The key to resistance management is to use herbicides which have different modes of action. When it comes to achieving a broad-spectrum effect like glyphosate, the choice of alternatives is extremely limited. Paraquat’s unique mode of action1 together with its broad-spectrum weed control and fast action, make it an invaluable tool in the fight against weed resistance to glyphosate.
Palmer amaranth is one of several important weed species in the same genus (Amaranthus) commonly known as pigweeds or waterhemps. It is a major problem in many southern states, particularly in Georgia, where it is considered to be the number one weed problem in cotton.
Weed scientists at the University of Georgia estimate that an average of just two Palmer amaranth plants in every 6 m (about 20 feet) length of cotton row can reduce yield by at least 23%. Furthermore, when a single plant can produce an alarming 450,000 seeds, you can bet the problem will be worse the next season.
Already, as much as 400,000 ha (one million acres) in Georgia and South Carolina are estimated to have become infested with glyphosate resistant Palmer amaranth since it was first noticed in 2005.

How do herbicides work?

Knowing how a herbicide works in detail - its 'mode of action' (MOA) - is important to understanding how to use it most effectively. Herbicide MOA is a major factor in weed control spectrum, crop selectivity and weed resistance.
Herbicides control weeds by interfering with how they grow. Different MOAs all ultimately either stop seeds from germinating or establishing as seedlings; prevent plants from making essential carbohydrates, proteins or lipids (oils and fats); or desiccate leaves and stems.
Paraquat’s MOA involves diverting the flow of energy captured from sunlight in photosynthesis to produce highly reactive free radicals which destroy cell membranes to quickly desiccate leaves. This happens within hours in bright sunlight because of the high levels of energy running out of control. Almost all green plants are affected by paraquat making it a broad-spectrum, non-selective herbicide.

Mode of action: how herbicides work

Introduction
Herbicides control weeds by interfering with how they grow. This is achieved by a number of different ‘modes of action’ (MOA) which all either ultimately stop seeds from germinating or establishing as seedlings; prevent plants from making essential carbohydrates, proteins or lipids (oils and fats); or desiccate leaves and stems. Knowing a herbicide MOA is important to understanding how to use a herbicide most effectively. It is a major factor in both herbicide selectivity and weed resistance.
The symptoms observed on weeds sprayed with herbicides express the MOA. In herbicide R&D, when new chemicals are screened experts carefully observe the detail and timing of the appearance of symptoms to gain clues as to the MOA. Fully understanding a MOA may take years of research by plant physiologists, biochemists, molecular biologists and many other scientific disciplines. The precise MOA of paraquat is very well understood - for more information, click here.
The more that is known about MOA, the more safely and effectively herbicides can be used. There are even examples of pharmaceuticals being developed as a result of research into herbicide MOA . For example, the drug nitisinone has now replaced the need for a liver transplant as the first-line response to type 1 hereditary tyrosinaemia, a rare metabolic disorder in children.

Integrated weed management in no-till systems

Integrated weed management and no-till are advanced agronomic tools with common aims to improve efficiency and profitabilty, while reducing the environmental impact of crop production. Although advanced in concept, these tools are straightforward and can be adapted for use in all cropping systems, from highly mechanised ones to subsistence farming, all around the world.
Tillage is a well proven means of controlling weeds, so are other methods good enough to use in an integrated approach to weed management in no-till systems? This article examines how farmers can reap the rewards of both techniques together.

Farmers around the world know just how hard it is to control weeds. They tend to come back with a vengance, especially when the many elements causing weed problems have not been appreciated and addressed. Aiming to manage weeds rather than control them is not only more realistic, but if Integrated Weed Management (IWM) is applied properly, it can reduce costs, protect the soil, and support pest and disease control.
No-till systems also provide economic and environmental advantages. However, in no-till, the traditional means of weed management by ploughing to prepare a field for cropping is not used.

No-till and biofuel crops

“America is addicted to oil” as President George W. Bush acknowledged in his 2006 State of the Union Speech. And, it is not just a US problem, nor is the addiction only to oil. Oil, coal and natural gas are the fossil reserves which power our planet, but now the spotlight is on crop biomass to provide a significant alternative source of energy and materials.
No-till farming and paraquat have a vital role to play in producing enough biomass while sustaining food production and protecting the environment.
At present, biofuels are manufactured from the parts of crops otherwise harvested for food, eg grain. This leads to two problems:

Not enough fuel
Potentially not enough food

The yield of fuel – biodiesel or bioethanol – from the oils or starch found in seeds is relatively low. With the economic and environmental motivation to grow more crops for biofuels, in future, they may take up valuable land that should be used for growing food, especially in poor Third World countries. Already, in Mexico the rising price of corn tortillas, a staple food for many poorer people, has been a problem. This has been due to the higher price of US corn, driven-up by the demand for ethanol.
To address both fuel and food issues, it would be much more attractive to use unharvested parts such as corn stover or wheat straw for biofuel production.

Weeds and weed control

Paraquat is used to control a huge range of weeds worldwide, but to control weeds effectively and sustainably it is important to understand them.
Why does a plant become a weed? How can different types of weeds be described? What are the features of weeds and the way they grow which can be targeted by herbicides for successful control?

Paraquat - a unique contributor to agriculture

Mr. Prasanna Srinivasan of New Dehli, India, is a recognized expert in the field of economics, policy and regulatory development and specializes in the impact of global environmental treaties on developing countries. Syngenta commissioned Mr. Srinivasan to provide a balanced assessment of the benefits and risks of pesticides in general and paraquat in particular. Mr. Srinivasan recently completed this review entitled, “Paraquat: A unique contributor to agriculture and sustainable development.
Please click on this link to download a copy of the review:
Paraquat: A Unique Contributor to Agriculture and Sustainable Development

Soybean cropping

Soybean stands out from other major crops: broad leaved rather than a grass; a legume, so plants supply their own needs for nitrogen fertilizer while increasing the fertility of the land; soybeans are rich in oil, protein and carbohydrate; and the crop has been highly developed by plant breeders and agronomists. This makes soybean arguably the world’s most versatile crop.
With such a broad nutritional base, soybeans are a staple food and animal feed. Whole beans provide flours; soya oil is used in cooking and food; protein-rich soya meal left after oil extraction is an important livestock feed; and soya protein is used in drinks, baby food, noodles, and as a meat and dairy substitute.
A significant amount of soybean production in the US, in particular, now goes to make biodiesel (5 to 10% each year). Biodiesel is not soya’s first connection with motor vehicles. In 1941, Henry Ford’s enthusiasm for finding industrial uses for crops resulted in the manufacture of the ‘Biological Car’ made for an exhibition. The vehicle’s entire bodywork was made from plastic derived from soybeans!
Paraquat is an essential tool for soybean farmers
Paraquat is an important tool in the soybean farmer’s battle against weeds, while also having a good environmental profile and creating opportunities in rural communities.

Paraquat for soybeans

Soybeans stand out from other major crops: broad leaved rather than a grass; a legume, so plants supply their own needs for nitrogen fertilizer while increasing the fertility of the land; and soybeans are rich in oil, protein and carbohydrate.
In the US, soybeans are grown on half of the 30 million hectares on which no-till farming is practiced. In Brazil, no-till has also been widely adopted for soybeans. Broad-spectrum herbicides, led by the introduction of paraquat in the 1960s, allowed the adoption and growth of no-till which does not rely on controlling weeds by burial from ploughing.

Soybean fact file

102 million hectares grown worldwide in 2010
90% or more of all soybean fields in USA and Argentina are GM
106% increase in productivity since 1995
40% of bean weight is oil rich in monounsaturated oleic acid
7% of US soybeans were used to make biodiesel in 2007
13 million hectares under no-till in USA

No-till systems save cash, time and fuel, improve soil structure, reduce erosion and provide havens for wildlife. Paraquat is deactivated on contact with the soil meaning that it can be sprayed to burndown weeds before planting without risking crop damage from root uptake. Paraquat works well even in cold and rainy weather.