Q: With all the politics around labeling (or not labeling) genetically modified organisms and the weakening of organic standards, I have to ask, can I assume that foods labeled "organic" are also GMO-free? 

—David in Cherry Hill, New Jersey 

A: USDA organic rules strictly prohibit the use of GMO seeds. Organic farmers are also required to create buffer strips to isolate their crops from pesticide drift and genetically tainted pollen. Despite these and other precautions, traces of GMOs can sometimes be found in certain organic-certified crops. Also, the USDA does allow some substances to be added to organic-certified food, such as enzymes from animals raised on GMO feed and acids possibly derived from GMO crops. So, the hypercautious would choose only organic foods that have little or nothing added to them.

As for your comment about labeling, you're right on the money: It's fraught with questionable politics. Labels like "GMO-free" or "contains GMO ingredients" could easily be printed on packaging or slapped on produce. Banning GMOs, or at least requiring labels for them, is important because GMOs enable the widespread planting of crops that tolerate herbicides (weed killers). Those chemicals end up polluting soils and waterways and, through the destruction of plants like milkweed, eliminate habitat for the monarch butterfly.