This is the VOA Special English AGRICULTURE REPORT.
Agriculture around the world depends on chemicals that control the growth of unwanted plants. Poisons that generally affect only unwanted plants, or weeds, are called herbicides. However, many herbicides are losing their ability to kill weeds.
Scientists have known for years that weeds develop resistance to herbicides. Now, a growing number of weeds are developing resistance to the world's most popular weed killer. The American company Monsanto makes the herbicide. Its trade name is Roundup.
Roundup has been developed for use with genetically engineered crops. These crops are called Roundup Ready. Growers can put the herbicide directly on the crop. It kills all unwanted plants. Yet, the crop remains unharmed.
Corn, cotton and soybeans have all been genetically engineered to be Roundup Ready. The use of these two products together greatly simplifies crop raising for farmers in many countries. About seventy-five percent of all soybeans and sixty-five percent of all cotton grown in America is Roundup Ready.
However, some experts say that herbicide-resistant weeds could cause serious problems. Resistant weeds could quickly overgrow a field, destroying the crop. Some experts say this is already happening in areas of Delaware, Maryland, Virginia and New Jersey.
Normally, farmers grow different crops in a field from year to year. This method is called rotation. It reduces the possibility that weeds or insects will become resistant to chemicals. Yet, only one herbicide is needed for all Roundup Ready crops. Herbicide-resistant weeds could ruin all Roundup Ready crops on a farm.
Scientists developed another kind of genetically engineered corn to resist insects. It is called B-T corn. Currently, the Environment Protection Agency requires farmers who grow B-T corn to plant other kinds of corn in nearby fields. This measure is meant to keep insects from developing resistance to B-T corn. However, no rule exists for Roundup Ready crops.
Experts from Monsanto say only about four kinds of weeds have shown resistance to Roundup. This is a very small number of cases. Some other herbicides are not effective against as many as seventy kinds of weeds. However, the number of resistant weeds has increased every year.
This VOA Special English AGRICULTURE REPORT was written by Mario Ritter.