Aside from the looming question of genetically engineered crops affecting biodiversity, GM crops introduce biological concerns for farmers on a more local level. Most importantly are the affects GM crops will have on the farmland, surrounding crops, and surrounding water sources. There are indications that the use of herbicide resistant crops may have long term adverse affects on the weed populations. One possibility is the creation of a "super weed" that could resist the affects of herbicides. These weeds receive this trait through wind borne cross-pollination occurring between weeds and crops that are genetically engineered to resist specific herbicides. This would make weed control extremely difficult for farmers and greatly reduce the effectiveness of the herbicide-resistant crop. Some countries such as France and Canada have forbidden growing certain crops because of the high risk of spreading genes with nearby wild relatives (Brookes, 1998). Crops engineered for pest or virus resistance may pose an even larger threat. Genes that resist a pest or virus might eliminate the control on a plant's growth. The spreading of that gene could cause massive overgrowth as seen with the introduction of the exotic kudzu. Another concern of wind borne cross-pollination is contamination of other nearby crops. Farmers are asking for estimated distances between GM and non-GM crops to reduce the risk of contamination. Now that some processors are asking for separation between GM and non-GM crops, contamination with GM germplasm in non-GM crops becomes an issue of liability for farmers.
Biotech companies are trying to address this problem by suggesting varying methods of farming and creating terminating seeds. The EPA has launched workshops on how to protect against resistance to Bt toxins in maize and cotton. The EPA appears to favor GM crops under correct management due to positive results such as the reduced use of cotton insecticide by 3.6 million litres a year since Bt cotton's introduction (Lehrman, 1999). Another question is how these crops will fair in marginal environments. Some researchers feel the uniformity will cause transgenic crops to perform poorly in marginal environments (Robinson, 1996 IN Atieri, 1997). As of now, farmers simply do not have the data needed to predict growth in these circumstances. The immediate environmental benefits realized from GM crop use, such as reduced pesticide costs, may ultimately be overshadowed by the long term costs on future crops, farmland and related species.
