Dilemma for Brazilian farmers

Glyphosate burndown spray has failed to control ConyzaSoybean growers in Brazil are facing a dilemma. More land under no-till

Description

Also known as conservation tillage or zero tillage is a way of growing crops from year to year without disturbing the soil through tillage ie cultivating the soil usually with tractor-drawn implements.

Authoritative On-line References and Resources

No-till.com:  A portal for on-line information about no-till farming.
is saving its soil and reducing energy use, but many no-till farmers are now finding that glyphosate resistant weeds are threatening future success.
No-till cropping systems have now been adopted on around 70% of cultivated land in the country, particularly for soybeans. Brazil and the US lead the world in no-till farming, but this is threatened by the rise of glyphosate resistant weeds. A recent article highlighted how worried American farmers are becoming (read more). This is the first of two features looking at the problem in Brazil – and a success story involving a paraquat-based herbicide.

No-till and GM crops

Soybean production without soil cover is estimated to cause the loss of 55 million tonnes of topsoil in Brazil every year1. No-till cropping has been very successful in curtailing soil erosion

Description

Displacement of solids (soil, mud, rock and other particles) usually by the agents of currents such as, wind, water, or ice by downward or down-slope movement.

Authoritative On-line References and Resources

http://soilerosion.net/ This site brings together reliable information on soil erosion from a wide range of disciplines and sources. It aims to be the definitive internet source for those wishing to find out more about soil loss and soil conservation.
, with its roots in the 1970s when the British company ICI began experimenting with the use of paraquat for weed control. Later, glyphosate was introduced and, with its advantage of controlling perennial weeds

Description

Weeds that return year after year. Some die back in the winter but their roots remain alive and shoots reappear in spring; some don't die back and grow in size and stature the next season.

Authoritative On-line References and Resources

The International Weed Science Society represents individual associations around the world.
, has been used increasingly, year-on-year, for three decades. Also, the support of Brazilian machinery manufacturers, who developed no-till seed drills now used all over the world, helped the area under no-till cultivation grow to over 25 million hectares in 20062,3.
Glyphosate’s original use in soybeans was as a burndown herbicide to remove weeds before planting. However, since glyphosate tolerant GM crops became available glyphosate has also been used as a selective herbicide to control weeds competing with the growing crop. Areas of no-till crops and of glyphosate tolerant GM soybeans continue to increase in Brazil 3,4In 2009, Brazil became second only to the US in the area of GM crops grown4. The area increased by 35% in 2008 alone. Of 21.4 million hectares of total GM crops now grown in Brazil, 16.2 million hectares are glyphosate tolerant soybeans. This is 71% of all Brazilian soybeans, grown by an estimated 150,000 farmers. The use of glyphosate is forecast to continue to increase as farmers move to grow glyphosate tolerant corn and cotton in the coming years.  

Glyphosate resistant weeds

Although a simple glyphosate-based weed control system may initially seem attractive to farmers, weeds soon take advantage of the lack of diversity in control methods. Any single approach will cause changes in the spectrum of weeds present. Fields which have been sprayed mainly with glyphosate for just a few seasons will tend to have more broad-leaved weeds present as these are less easily controlled. In Brazilian soybean crops good examples are species of Ipomea (morningglories) and Commelina (dayflower). Worse than this, gene mutations conferring resistance to glyphosate, naturally present in rare individuals of otherwise susceptible weed species, can come to dominate weed populations. The result in Brazil has been a developing problem of resistant weeds in the southern soybean growing states of Paraná and Rio Grande do Sul. According to Embrapa (Brazilian Agricultural Research Corporation) some 2-3 million hectares are infested with weeds no longer controlled by glyphosate. Five weed species are now officially recognised as being resistant to glyphosate5. The major problem is with Conyza (fleabane and horseweed species). A recent survey in Rio Grande do Sul found that from 208 populations of Conyza sampled, 60% were resistant. Euphorbia heterophylla (wild poinsettia), another broadleaved weed

Description

The leaves are "broad" as opposed to the "narrow" leaves of grasses. Also called 'dicots' having two seed leaves, while grasses are 'monocots' having one seed leaf.

Authoritative On-line References and Resources

http://www.iwss.info The International Weed Science Society.
, is resistant too. Some populations of this weed are also resistant to soybean selective herbicides

Description

A chemical product used for eliminating certain types of weeds only (ie either grasses or broadleaved weeds) and not affecting specified crops.

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.
with ALS inhibitor mode of action (read more). There are also significant areas infested with the grass weeds

Description

The leaves are "narrow" as opposed to the "broad" leaves of broadleaved weeds. Also called 'monocots' having one seed leaf opposed to 'dicots' having two seed leaves.

Authoritative On-line References and Resources

The International Weed Science Society represents individual associations around the world. 
Lolium multiflorum (Italian ryegrass) and Digitaria insularis (sourgrass).
Using herbicides with different modes of action is an important way to fight weed resistance. In the next article to be posted on the Paraquat Information Center you can read about how ‘glyphosate’s bodyguard’ is helping Brazilian farmers resolve their dilemma over no-till and glyphosate resistant weeds.

References

  1. World Wildlife Fund
  2. UN Food & Agriculture Organisation
  3. Brazilian No-till Federation FEBRADP
  4. International Service for the Aquisition of Agri-biotech ISAAA
  5. International Survey of Herbicide Resistant Weeds