"Killer Weed" Becomes Focus Of Biotech Debate

by Danielle Knight

Advocates of genetic engineering say the technology could eliminate the parasitic weed Striga -- commonly known as witch weed or "buda" in the Swahili language -- which has devastated crops in East Africa especially.

Critics counter that the new method would be too expensive for poor farmers and that improving soil health would better control the weed, which grows to about 15 centimeters in height and ravages corn, millet, and sorghum -- all regional staples.

Agricultural studies estimate that the weed destroys 40 percent of Africa's total cereals harvest -- at a time when hunger, already widespread, is increasing.

In a badly infested field, Striga -- which seeks out the roots of nearby crops and then robs them of water and nutrients -- can destroy most of the harvest. According to agricultural researchers, it causes several billion dollars in losses each year throughout East Africa.

Because each Striga plant produces as many as 20,000 seeds that can lie dormant for decades, eradication has so far been considered near impossible.

Biotechnology advocates argue that the solution to the parasitic weed is to engineer varieties of African staple crops to resist herbicides, so that farmers can spray their infested fields with chemicals to kill the Striga without also killing their crops.

This is the same approach that biotech company Monsanto has taken in engineering corn, soybeans, and other crops to withstand its best-selling herbicide glyphosate, which it markets under the name Roundup.

Fred Kanampiu, an agricultural researcher in Kenya for the Mexico-based International Maize and Wheat Improvement Center (CIMMYT), says this approach is the only probable solution because Striga can overwhelm even improved crop varieties.

Donor agencies also are betting on biotechnology. Last year, the New York-based Rockefeller Foundation committed hundreds of thousands of dollars to various biotechnology researchers, specifically to work on controlling Striga.

Gordon Conway, the foundation's president and an agricultural ecologist, argues that biotechnology has an important role to play in developing regions, especially Africa.

"We assess the potential benefits to the developing countries as greatly exceeding the likely risks," says Conway.

However, Brian Halweil, a research associate with the Worldwatch Institute here, argues that poor farmers in Africa would be much better served by the development of inexpensive local methods, rather than biotechnology.

"The biotech fix would be costly for the farmer, would increases chemical use, (and) would add no other benefits to the system," says Halweil, who recently went on a research trip to western Kenya and met with farmers and scientists there.

Agricultural researchers in East Africa have already developed affordable home-grown methods to control the parasite, he adds.

Local farmers, for example, have discovered that Striga thrives on overused and depleted soils. The parasite weed especially thrives on land that farmers have not allowed to lie fallow so that the soil can replenish itself, says Halweil.

Striga has flourished because Kenya's agricultural land increasingly is overused, he adds.

"As Kenya's population has grown, the size of the average family field has declined, and farmers have become increasingly reluctant to take land out of production," he says.

Adding fertilizers to replenish the soil, explains Halweil, is uncommon because commercial fertilizers are too expensive. Collecting manure from livestock for fertilizer is rare because animals generally graze out in the open.

Despite these challenges, some farmers have found a way to suppress Striga by planting certain types of tree species that add nutrients to the soil. These trees have microbes on their roots that withdraw nitrogen from air pockets in the soil and produce chemical compounds containing nitrogen that plants can metabolize.

These "nitrogen fixing" trees are grown during the one time of year when conditions impose the year's only fallow period on farmers -- from February to April. Although three months is not a long time, planting these trees for just one season can cut Striga infestations by more than 90 percent, Halweil says.

Bashir Jama, a scientist with the Nairobi-based International Center for Research in Agroforestry, says that if farmers can be persuaded to let the trees grow for longer than one season, other weeds and pests besides Striga also will be better managed.

Halweil points to other benefits of growing the trees. The greens of the fallow crop are nutritious livestock feed and the wood is useful for fuel.

"A six-month tree crop fallow on as little as half a hectare can meet a family's cooking needs for an entire year," he says.

Other ecological Striga controls also have emerged in Kenya.

In its efforts to find ways to control a different corn pest, the International Center for Insect Physiology and Ecology, which focusses on ecological solutions to pest problems, discovered a plant called silver leaf desmodium. As it happens, this plant secretes a chemical that interferes with Striga's ability to tap into the roots of crop plants.

Planting the species near corn crops could significantly reduce problems with Striga, the Nairobi-based center says.