Focus on paraquat in Mexico
Mexico plays a pivotal role in global food security despite most Mexican farmers being smallholders. Not only is agriculture an important sector in the country’s economy, but also Mexico is home to CIMMYT, one of the world’s leading agricultural research centers and the place where the crop production ‘Green Revolution’ of the 1960s and 1970’s began. Paraquat is a valuable tool for Mexican farmers, enabling reduced tillage systems and inter-row weed control, especially in corn, the most widely grown crop.
This article looks at how paraquat fits into cropping systems in Mexico and the contribution that Mexico has made, and continues to make, to feeding the world.
Mexican agriculture and paraquat
Around half of Mexico’s farmers cultivate five hectares or less, with over 60% growing corn and dry beans (Phaseolus vulgaris) of various types1. The number of Mexican farmers is steadily decreasing as many seek better paid jobs in the cities. Therefore, labor-saving farming practices and technologies are important to maintaining food production.
A diverse range of crops is grown including those also found elsewhere in both temperate and tropical climates. By far the largest area is cropped with corn (Figure 1). Markets for corn in Mexico comprise yellow corn for livestock feed and industrial uses, eg for the production of high-fructose corn syrup; and white corn for making flour, eg for tortillas. Most corn grown in Mexico is white corn, with yellow corn being imported from the US2. Mexico has not allowed the commercialization of GM corn to date.
Grown on a far smaller area, but slightly more valuable than corn is sugarcane. Sugar is Mexico’s largest agricultural industry. However, like corn, the small size of farms limits the efficiency of the industry. Especially valuable per hectare are tomatoes, chilli peppers, bananas, avocados and guava.
Paraquat is used to control weeds growing in a wide variety of crops in Mexico:
Paraquat cannot penetrate bark, so can be confidently sprayed around trees to control weeds in plantations and orchards. It is important to prevent weeds from competing with the trees for water and nutrients, to remove pest refuges and to allow easy access for harvesting.
- Agricultural row cropsDescription Annual crops traditionally grown in wide rows such as corn, soybeans and cotton. Authoritative On-line References and Resources The US national associations for those involved in the production of, and trade in, corn, soybeans and cotton: http://www.ncga.com http://www.soygrowers.com http://www.cotton.org : corn, soybeans, sunflower, safflower, sugarcane, potatoes, pineapple
- Horticultural row crops: cucumber, lettuce, melon, cabbage, watermelon, tomato, peas, onions, asparagus, beans, broccoli, carrots, cauliflower, zucchini
Paraquat can be used to control weeds growing in between the rows of the above crops, using a shield around the spray nozzle if necessary. However, paraquat is a contact herbicide and spray droplets landing on crop leaves cause only minimal local damage because there is no translocation to growing points.
- Forage: alfalfa
Paraquat can be used to control weeds in this perennial crop after harvest when the crop is dormant.
As a broad-spectrum, non-selectiveDescription A chemical product used for eliminating all types of weeds (annual and perennial grasses and broadleaved weeds). Authoritative On-line References and Resources http://www.weeds.iastate.edu/ An invaluable source of contemporary information about herbicides and weeds from Iowa State University. herbicide, deactivated immediately on soil contact, paraquat can be used to burndown weeds before planting any crop (see below).
Products that include both paraquat and diuron are also sold. Diuron is a photosynthesis inhibitor that enhances the activity of paraquat on some tough weeds.
Mexico’s role in global food security: CIMMYT
Mexico is home to CIMMYT (Centro Internacional de Mejoramiento de Maiz y Trigo)4, where the ‘Green Revolution’ of the 1960s and 1970s began. The mission of the research and training center is to sustainably increase the productivity of maize and wheat systems to ensure global food security and reduce poverty.
The most famous scientist to work at CIMMYT was Dr Norman Borlaug who was awarded a Nobel Prize in 1970 for his work on increasing the yield of wheat.
The citation for the Nobel Prize was that by his work he saved the lives of one thousand million people. Borlaug identified genes for disease resistance and shorter stems and incorporated these into wheat varieties to be grown initially in Mexico, followed by India and Pakistan, in particular.
Besides being resistant to the devastating stem rust disease (Puccinia graminis), the ‘semi-dwarf’ varieties were able to remain standing when receiving higher rates of nitrogen fertilizer.
CIMMYT together with other partners in CGIAR (Consultative Group on International Agricultural Research), the global consortium that brings together agricultural research organisations and funders of their work), also has a worldwide program on conservation agriculture. This involves developing agronomic practices to reduce tillage, retain adequate coverage of soil with vegetation and harvest waste, and to introduce diversified crop rotations to prevent erosion and improve soil quality.
Non-selective herbicides like paraquat are important tools for farmers practising conservation agriculture because weeds need to be controlled without the use of the plow. Where glyphosate is used for weed control, it is important to use paraquat as an alternative in integrated weed managementDescription A decision support system for crop protection which focuses on long-term prevention or suppression of pest problems with minimum impact on human health, the environment, and non-target organisms. IPM takes into consideration all available pest control techniques and tactics (cultural, mechanical, biological, chemical). IPM emphasizes the growth of healthy crops for better productivity with the least possible disruption to agroecosystems. Authoritative On-line References and Resources http://www.ipmcenters.org "The USDA's National Site for the Regional IPM Centers' Information System provides information about US commodities, pests and pest management practices, people and issues." (IWM) systems that will reduce the likelihood of weeds becoming resistant to glyphosate. Reduced tillage systems, such as no-till, lead to benefits including reduced water use, lower energy inputs and emissions, and lower labor requirements and costs.
Some examples of how farmers in Mexico are benefiting from conservation agriculture can be found on the CIMMYT website. Read more here
Brand names of the leading paraquat products in Mexico are Gramoxone and Gramocil (paraquat + diuron).