Impacts on farming
GM seed prices are much higher than non-GM seeds: they include a 'technology fee' for the (patented) GM trait.The companies selling seeds may bring legal cases against farmers thought to be saving seeds for replanting without paying them a licence fee.
With herbicide-tolerant GM crops, herbicide use may be cut in the short-term but increases in the longer term (increasing costs) with resistant weeds (superweeds. This is known as 'the transgenic treadmill'. With insect resistant (Bt) GM crops, there are growing problems with resistant pests and outbreaks of secondary pests (pests not killed by the Bt toxins).
Crops grown by conventional and organic farmers are at risk of contamination with GM crops through seed transfer (e.g. on footwear/machinery) or spillage; cross-pollination; via farm-saved seed; backcrossing; movement by animals etc.
Contamination incidents can cost hundreds of millions of dollars in lost markets: but the industry is not usually made liable for these expensive losses.
Many farmers will wish to retain access to more lucrative conventional (non-GM) and organic markets. However it is unclear whether co-existence of GM crops with non-GM crops is possible. The costs of segregation are borne by non-GM farmers and add to overall food prices where GM crops are grown.