Weed control

Taro: potato of the Tropics

Paraquat in Samoa is not only helping farmers to provide a staple food but is also enabling taro to become a very important export crop.  Ever wonder what fuels the impressive size and power of the awesome Pacific Island rugby players? Look no further than taro. Taro is a tropical starchy root crop which is a staple food in many subsistence communities, particularly in the Pacific islands. And while the rugby team members most likely have a broad selection of meals from which to choose, for many people living in these areas taro is an essential part of their diet.
As a tropical crop, protecting taro from weeds is critical. Weeds thrive in such hot and humid climates, robbing yield. Hand hoeing crops is one option, but, not only is this time consuming and labour intensive, but it means other opportunities, particularly for education in poorer communities, may be missed. Using the right choice of herbicide provides an effective alternative. Weed control is critical in dryland taro, particularly in the first 3 months.

FAO expert stresses weed menace

Weeds do not hit the headlines like droughts, insect plagues or even swine flu, but cause substantial human misery, quietly and constantly, notes one of the UN Food and Agriculture Organisation’s (FAO) most renowned weed experts. Ricardo Labrada-Romero quotes figures produced by leading environmental organisation Landcare Research (New Zealand) which indicate that uncontrolled weeds cause crop losses equivalent to 380 million tonnes of wheat every year.

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.

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.

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.

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 and sustainable agriculture

Paraquat and sustainable agriculture, by Richard H. Bromilow
In his paper “Paraquat and sustainable agriculture,” author Richard H. Bromilow studies the role paraquat plays in supporting sustainable agriculture around the world.
Abstract: Sustainable agriculture is essential for man's survival, especially given our rapidly increasing population. Expansion of agriculture into remaining areas of natural vegetation is undesirable, as this would reduce biodiversity on the planet. Maintaining or indeed improving crop yields on existing farmed land, whether on a smallholder scale or on larger farms, is thus necessary.
One of the limiting factors is often weed control; biological control of weeds is generally of limited use and mechanical control is either often difficult with machinery or very laborious by hand. Thus the use of herbicides has become very important.

Paraquat for rice

In Asia alone, more than two billion people obtain over 60% of their calories from rice. It is the most rapidly growing source of food in Africa and is critical to food security. Long grain rices are typically of the indica race and include the fragrant Jasmine rice from Thailand and Basmati rice from India. Short grain rice, typically japonica, is usually more sticky than long grain and is favoured in Japan. Saki rice is grown in Japan to make rice wine, and in Indonesia there are red and black grained varieties. About 80% of the world's rice is grown by smallholders in these places. In Asia, women are often responsible for rice farming as men have moved to work in the cities.
Efficient and productive rice-based production systems are essential for economic development and for improved quality of life for much of the world's population. Plant breeding, crop protection, water management and fertilization have increased productivity and reduced the costs of production.
Weeds can reduce the yield and quality of rice by competing with the crop for light, nutrients and space; and their seeds can contaminate the harvested grain. Some of the most widespread and aggressive weeds are the Echinochloa species (barnyardgrass). Infestations of only ten of these weeds per square metre have been recorded to reduce yields by 25%.

Will farming and soil quality collide?

Will farming and soil quality collide?
World Agriculture and the Environment is an important new book addressing the fear that increasing demand for food and fiber is on a “collision course” with soil quality.
This article is in two parts. In Part One, some of the main issues discussed in the book are reviewed. Part Two then explains how more than 40 years of research and practical use have shown that controlling weeds with paraquat can help provide improved and sustainable crop management practices to improve soil quality.
Part One: What ‘World Agriculture and the Environment’ says
In World Agriculture and the Environment authorJason Clay (World Wildlife Fund-US vice president, Center for Conservation Innovation) reviews the production and environmental impact of 21 of the world’s major food commodities. The main threats to the environment posed by crops, fish and meat are identified and explored, as well as the trends that shape those threats.
Major Issues
A fundamental acknowledgement in the book is that low intensity cropping can not support current, let alone future, levels of world population. There are two underlying reasons. First, using more land for farming destroys natural forests and grasslands.