How do GMOs affect other plants?

Answers derived from an interview with Bryan Young, Weed Science Society of America Fellow and Professor of Botany & Plant Pathology.

Weeds, such as the dandelions in your yard, are considered serious pests on the farm. They compete with crops, threatening healthy growth and significantly reducing the yield or quality of a crop at harvest. While dandelions may be an eyesore in a well-manicured green lawn, farmers must prioritize weed control to protect their livelihood.

What are herbicides, and why do we use them?

Pesticides are chemicals that are used to suppress or control different pest organisms. Herbicides are pesticides that specifically target weeds.

Farmers can manage weeds by tilling, manually removing them, burning them or rotating which crops grow on a field each season. However, herbicides are often the quickest, most effective and affordable solution for weed control for any field, whether or not the plants are genetically modified. 

New technology is also being developed for weed control, including robots that use cameras and artificial intelligence to selectively spray only the weeds in a field.

Are there herbicides inside of GMOs?

Plants are naturally competitive, and some can release their own chemicals to kill other plants nearby. Black walnut trees are one of these, and any gardener will tell you to keep your tomatoes far from them. However, there are no commercially available genetically modified organisms (GMOs) that produce herbicides.

Instead, some crop varieties have been genetically engineered to be tolerant of specific herbicides. When that herbicide is sprayed in a field, the weeds will be killed without damaging the GM crops. 

The most prevalent example of this technology is GM crops that are resistant to glyphosate. Glyphosate, more commonly known under the brand name Roundup, is the most widely used herbicide in the world by volume, especially in agriculture but also in many products for residential use.

While insecticides and fungicides can be active on the surface of plants, herbicides must be absorbed into all plants in order to kill weeds. Herbicide-tolerant crops either break down or bypass the toxic effect of the herbicide.

Since absorbed herbicides are generally broken down, the final crop products are tested to confirm they are safe for humans to consume. But it’s also good practice to wash the outside of your fruits and vegetables to remove any soil, debris, bacteria or potential pesticide residue that was not removed by rain.

What is a “superweed,” and are they related to GMOs?

Superweeds is a term coined to describe weeds that have developed resistance to herbicides used with GM crops. But these plants aren’t really "super," or different from any other weed in the absence of any herbicide being applied.

Weeds adapt and evolve just like all other living organisms. For example, when doctors prescribe the same antibiotic over and over again to treat a bacterial infection, some of the bacteria will survive and develop a resistance over time, making the antibiotic ineffective.

The same thing happens with herbicides and all other management strategies. Hundreds of weeds have become resistant to herbicides since they were introduced, before the development of GMOs. As a result, weed control strategies become less effective over time. Farmers can address this problem by switching between different management strategies or using multiple methods simultaneously.