Original flickr caption:

DANGER: Red marks the spot of a land mine.

In Autumn, the plant's normal reaction is to turn red or brown when subjected to stressful conditions such as cold or drought. This weed has been genetically modified to change colors only in the presence of nitrogen-dioxide, a marker for landmines or other unexploded ordinance. The plant is also made to be sterile. The application would be to release the seeds from a crop duster over a former battleground area, and let the plants grow, marking the threats. Initial tests will be in Bosnia, Sri Lanka and Sub-Saharan Africa.

The hope is that this will be more effective than the dogs and metal detectors used today.

“Experts believe that there are more than 1 billion unexploded landmines in over 75 countries worldwide, and it is estimated that a landmine kills or injures someone every 20 minutes, usually children or teenagers.” (source)