So you heard GMOs cause “superweeds”….

The low down: Superweed is a misleading term used to describe weeds that are resistant to an herbicide. It is conceptually possible that certain, herbicide-resistant GMOs could contribute to an increase in herbicide-resistant weeds; however, such concerns are not limited to GMOs, but are relevant for any crops used in conjunction with herbicides.

The details:  First of all, what is a superweed? According to the Weed Science Society of America (WSAA), there is “no science-based definition for superweed,” but the term is often used to describe herbicide-resistant weeds.  Just as overuse of one particular antibiotic promotes the spread of bacteria resistant to that antibiotic, overuse of an herbicide can result in herbicide-resistant weeds. According to Rick Boydston of the USDA-ARS:

Resistance is a natural phenomenon which occurs spontaneously in weed populations, but is only noticed when a selection pressure is applied to the weeds via herbicide application

Boydston further explains that herbicide resistant plants within a given population of weeds are rare:  “1 in 100,000 to 1 in 1,000,000”. Treating this population with an herbicide provides selective pressure, so that only the few resistant plants naturally present in the population go on to produce the next generation, thus passing on the resistance trait.

Weed scientists like Dr. Andrew Kniss find use of the term superweed to describe herbicide-resistance “exceptionally frustrating” because it “indicates that the weed is super in some way”. However, despite claims that “Some runaway weeds in the southern U.S. are said to be big enough to stop combines dead in their tracks,” herbicide-resistant weeds are not any bigger or nastier than their non-resistant counterparts.

Anti-GMO activist groups like Food Integrity Now call herbicide-resistance “a direct result of growing GM crops”. Where do these claims come from?

There are two ways that specifically herbicide-tolerant GMOs could hypothetically contribute to a rise in herbicide-resistant weeds. It is important to note that not all GMOs are herbicide tolerant. The following points apply only to crops that have been genetically modified to tolerate the herbicide glyphosate. It has been proposed that herbicide-tolerant GMOs could contribute directly to the rise in herbicide-resistant weeds through cross-pollination with closely related weed species. This explanation is embodied in the oxford dictionary definition of a “superweed”:

A weed which is extremely resistant to herbicides, especially one created by the transfer of genes from genetically modified crops into wild plants

However, According to the WSAA, “The transfer of resistance traits from genetically modified crops to weeds growing in the field is rare.” And according to Dr. Brad Hanson, Cooperative extension specialist at UC Davis, “to date no herbicide-resistant weeds in corn, cotton, or soybean production regions appear to have become resistant due to traits moving from the crop.”

If GMOs did cross with weeds and pass on herbicide-tolerant traits, this problem would not be unique to GMOs, but could also result from crops that have been conventionally bred for herbicide resistance. For example, it is documented that imidazolinone-resistant jointed goat-grass arose from a cross-pollination event with wheat bred to tolerate imidazolinone.

Herbicide-tolerant GMOs could also contribute to the rise in herbicide-tolerant weeds indirectly by encouraging an increase in the use of glyphosate. Glyphosate use has increased with the planting of GE crops, and numbers of glyphosate resistant species are highest for crops for which an herbicide-tolerant GE variety exists.

Screen Shot 2016-04-27 at 4.22.10 PMScreen Shot 2016-04-27 at 4.22.58 PM

Screen Shot 2016-04-27 at 4.46.57 PM

Source: Part of the International Survey of Herbicide Resistant Weeds at


However, not all cases of glyphosate resistance have been identified in fields where herbicide tolerant GMOs are grown. To determine if glyphosate-resistant weed species identified for crops that are not genetically engineered for herbicide tolerance arose first in fields where herbicide resistant GE crops were planted, Dr. Andrew Kniss compiled data from and plotted new cases of glyphosate-resistant weeds that initiated in GM-crop sites versus those that originated in non-GM crop sites.

Screen Shot 2016-04-27 at 4.27.14 PM

Source: Data from compiled by Dr. AndrewKniss

Remarkably, cases of glyphosate resistant weeds are no more likely to be documented in association with GM fields than non-GM fields. This is likely because glyphosate is also used in conjunction with crops that are not genetically modified for herbicide tolerance. For example, glyphosate is used to control weeds between rows in orchards and to encourage mature wheat to dessicate so it is ready to be harvested more quickly. If GMOs drastically contribute to the rise of herbicide tolerant weeds, we would expect to see a spike in herbicide tolerance corresponding with the introduction of GMOs; however, this is not the case.

Screen Shot 2016-04-27 at 4.28.05 PM

Source: Data from compiled by Dr. Andrew Kniss



In conclusion, herbicide-tolerance can arise from many sources. Current data do not seem to definitively point to GMOs as a significant cause for the rise in herbicide-tolerance. As Dr. Andrew Kniss puts it:

GM crops don’t select for herbicide resistant weeds; herbicides do. Herbicide resistant weed development is not a GMO problem, it is a herbicide problem.

The European Academies Science Advisory Council agrees:

Cultivating a GM crop variety with increased herbicide resistance, for example, may prove detrimental to the environment if the farmer over-uses that herbicide. But the same would be true of herbicide resistance introduced by conventional breeding.

Despite a lack of clear evidence that GMOs contribute to the rise in herbicide-resistance, many critics cite the development of “superweeds” as a reason for advocating a moratorium on GMOs. Chipotle cites as one of their reasons for removing GMOs from their menu that “GMOs engineered to…withstand powerful chemical herbicides…create herbicide resistant super-weeds.”  Chipotle’s solution to the “super-weed” problem is to switch from using oil from soybeans genetically modified for herbicide resistance, to  oil from sunflowers that are “naturally” resistant to the herbicide atrazine.  As Dan Charles of NPR points out, use of herbicides in this system has led to far more resistance problems. This graph compares numbers of species resistant to the herbicide glyphosate (ESPS Synthase Inhibitors shown in light blue) with species resistant to herbicides used on sunflowers (ALS inhibitors shown in red).

Screen Shot 2016-04-27 at 4.37.36 PM

Source: Graph from, comments added by Dr. Andrew Kniss

Thus, prohibiting the use of herbicide-tolerant GMOs does not eliminate problems of herbicide resistance. Furthermore, according to the USDA, planting herbicide-tolerant crops “makes it easier to manage weeds using less tillage, which can help reduce soil erosion as well as improve soil quality and water conservation”

So if banning GMOs will not prevent the development of more herbicide-resistant weeds, what will? According to the USDA:

Mitigating the evolution of herbicide resistance depends on reducing selection through diversification of weed control techniques, minimizing the spread of resistance genes and genotypes via pollen or propagule dispersal, and eliminating additions of weed seed to the soil seedbank.

The list of best management practices for managing herbicide-resistance includes “cultural practices that suppress weeds by using crop competitiveness,” following herbicide label instructions, and stacking herbicides with multiple mechanisms of action (MOA).  Dr. Stephen Weller, professor of horticulture at Purdue, compares multiple modes of action for weed control with putting more than one lock on the same door: “The thief, in this case the weed, might manage to get by one of the locks, but if you have several, as in several modes of action, it is much harder. If you can control a weed with two or three mechanisms of action, the likelihood of resistance occurring to all the mechanisms used is greatly reduced.”

The USDA has also noted that “Economic Incentives May Encourage Grower Cooperation in Managing Resistance”.

Here are a few other helpful resources on GMOs and superweeds:

Where the Superpowers of Superweeds Comes From. James Schnable, May 14, 2010

WSSA FACT SHEET: Dispelling Common Misconceptions about Superweeds

USDA APHIS Recommendations for Best Management Practices for Authorized Field Trials of Regulated Herbicide-Resistant Crops

USDA: Managing Glyphosate Resistance May Sustain Its Efficacy and Increase Long-Term Returns to Corn and Soybean Production. Jorge Fernandez-Cornejo and Craig Osteen, May 4, 2015

What does Chipotle’s switch to non-GMO ingredients mean for pesticide use? Andrew Kniss, May 18, 2015

Where are the super weeds? Andrew Kniss, May 1, 2013

What are superweeds? & Do GMOs cause superweeds? Genetic Literacy Project, Accessed April 27, 2016


The birds and the bees and the flowers? The not-so-secret sex life of plants

It’s springtime, so those of us with allergies might have noticed plants getting all animal planet with our sinuses. Seems most plants are pretty lose with their pollen, but when it comes to procreation, they’re very particular. So how do plants swipe right on a match? (For my married friends, that’s a tinder reference. For my mom, tinder is an app people use to meet people. For my dad, an app is a phone capability)

First base is geography. Plant breeders can take related plants from different regions, play some Barry Manilow, and cross them in a green house yielding new varieties. But under normal conditions, plants have to live and thrive in the same environments to cross.

Second base is timing. To our dismay allergy season is a season not a day. That’s because different plants flower at different times. They respond to environmental cues like day length and temperature and flower at the time that will yield the maximum chance of survival and success for their offspring. The timing differs depending on the plant and the method of seed dispersal/germination. So even in plants, equivalent levels of maturity are necessary for a fruitful relationship.

Third base is anatomy. For some plant species, male and female reproductive parts are found on different plants (sound familiar). I’ll spare you the analogy, but for many species, both genitalia appear on the same plant. In some cases they’re right up next to each other within the same flower. The location of plant privates determines whether plants are more likely to breed with their neighbors or themselves.

Plants are actually pretty content with pollinating themselves, and some almost exclusively self-fertilize. These loners like rice can be a real pain for breeders hoping to cross different varieties. On the other hand, corn man parts, called tassels, stick right out of the top of the plant. Wind blows the pollen from the tassels and it lands on the silky hairs that stick out of the ears of neighboring plants as much as 200 feet away

Home runs require chemistry. Assuming our gentle-pollen and lady-ovule live in the same zip code, are age-appropriate, and are serendipitously brought together (totally not by online dating), there’s still got to be chemistry. And I’m not being cute here, I’m talking about literal chemistry. In order for fertilization to occur, pollen has to produce a straw-like appendage called the pollen tube which delivers the sperm to the egg. Pollen tube growth is guided by chemicals called chemoattractants which are produced by the ovule.

Aw scent of a woman! The molecules that ovules use to lure pollen tubes had been previously identified. Just last month, two studies published in the prestigious journal Nature uncovered the male receptors that recognize their female partners. Why are these breakthroughs important? If we can figure out what prevents different species from crossing, we might be able to create inter-species mixes (like an actual “grapple” or the blue raspberries my brother keeps pushing for).

Happily ever after. So that’s what happens when two plants love each other very much. For a real R-rated experience, check out these absolutely incredible videos of plant and insect mé·nage à trois encounters.

  1. Flowers trick male wasps into thinking they are female wasps. A BBC production.

2. Flower requires bee “vibrations” to release pollen. Also a BBC production.

For scientist readers, here are the less fun but fascinating nature papers:

From Pitchforks to Personal Protective Equipment: Who is Growing Our Food?

Picture a farmer-you might conjure the popular image of Grant Wood’s “American Gothic”- a weathered old man with a pitchfork propped next to his thin-lipped apron-clad daughter. While Wood claims to have painted in appreciation of Midwestern culture, writers such as Gertrude Stein saw satire, and Iowans were outraged at their depiction as pinched, grim-faced, puritanical Bible-thumpers.”

I can’t help but wonder, if Wood were alive today, what would his Instagram look like? Would he plaster his feed with Paul Harvey quotes–God looked down on his planned paradise and said, ‘I need a caretaker.’ So God made a farmer”–or satirize his own painting, costuming his subjects in hazmat suits? Grant Wood’s depiction of a farmer may have been accurate when he painted it, but it is now a caricature. So who is really growing our food?

Farmers make up less than 1% of the US population, and a quick Google search shows that their image is complicated by labels like “organic,” “conventional,” and “GMO”. Are these images accurate? Both of the farmers themselves and of the techniques and tools they use?


These images were taken from a screen shot of the top row of results returned from a Google image search for “organic farmer”, “conventional farmer”, and “GMO farmer” respectively on April 11, 2016. These images reflect common stereotypes of different farm production systems.

When I think about farmers, I remember my friend Kyle Martinez timidly reciting Macbeth in a Shakespeare class at the University of Colorado. Despite his degree in political science, Kyle’s heartstrings pulled him back to tiny Olathe, Colorado. Now, he’s farming 200 acres, serving on the board of directors for the local energy co-op, and studying for his master’s in healthcare administration, all while working full-time for his family’s home care business. When I congratulated him on his engagement he laughed,

“it takes a strong woman to stand behind the idiots who farm”.


Kyle and Kat grow conventional and GMO corn, onions, and a variety of cover crops in Olathe, CO. Photo provided by Kyle Martinez

Kyle and Kat Martinez are first generation farmers, so they’ve had to borrow just shy of a million dollars for land, equipment, and yearly inputs just to get their crops in the ground. So far, Kyle fits Harvey’s romantic description of a farmer: “Somebody willing to get up before dawn…work all day in the fields…and stay past midnight at a meeting of the school board.” I wanted to see where he fits in the stock photo world of farmers, so I questioned his pest control methods.

We do crop rotations, and I’ve started doing cover crops in front of my sweet corn,” he tells me. “I grow a minimum-till cover crop that has 8 or 9 different crops like radishes, winter peas, turnips, winter rye grass…That’s just us trying to take better care of our soil.”

Crop rotations and cover crops are often billed as organic farming methods, so I pry, “Is any of your corn genetically modified?”

“All of what I call field corn (corn for animal feed) is Roundup Ready (RR).”

RR corn is genetically modified for resistance to glyphosate, the active ingredient in the household herbicide Roundup. So here is a farmer using not only crop rotations and cover cropping, which are often associated with organic farming, but also GMOs and glyphosate for weed control? I try searching “organic and GMO farming” and find I’ve confused Google. All of the images seem to imply the two are polar opposites firmly at odds. Yet Kyle, a conventional farmer by definition, uses the same techniques that benefit soil health in organic systems. I ask how the herbicides are applied and if he is concerned about toxicity.

“We take it upon ourselves to wear gloves and masks while we’re mixing,” he explains. “From the consumer standpoint, it’s not really a concern. With the sweet corn, the ear is not exposed and we spray the top of the onions, not the onion that’s developing underground. We do our part to make it safe for everybody else, but I’ll eat onions or an ear of sweet corn right out of the field.”

With his array of methods, Kyle doesn’t seem to fit any pigeonholed farmer images. Wondering if his hodgepodge system is unique, I interview several more farmers beginning with Doug Wilson, a classmate of Kyle’s who also lives in Olathe. Doug is also much younger than your typical farmer (averaging 58 at the last census) and has an endearing way of emphasizing the long E in “sweet corn”as he proudly gushes over his conventional crops:

“We have ‘Olathe sweet’ sweet corn, the sweetest corn in the US. The quality of our sweet corn is of the utmost importance. We do residue testing for quality assurance for our customers and we’ve never had a problem with pesticide residues.”

Doug Kylynn and Avery-27

Doug and Kylynn (with their daughter Avery) grow GMO corn, conventional sweet corn, beans, and onions on small plots in Olathe, CO. Photo provided by Doug Wilson.

Each of Doug’s fields averages 20-30 acres, not the large “industrial-type” farm we typically picture for conventional systems. I ask Doug if his family eats the crops they grow:

“We have a feedlot down the road that we sell (genetically modified field) corn to that we buy our beef from–that’s a local farmer– and we buy pork from them as well. We eat our own sweet corn, we eat our own onions, and we always keep our own beans to make chili and refried beans”

Olathe is not the only place where farmers have diversified their practices. Allen Williams, a farmer in Carro Gordo, Illinois, grows certified organic crops as well as “genetically modified soybeans for a seed company called Syngenta, and…non-GMO beans for food grain.”


Allen Williams or Carro Gordo, IL grows GMO, conventional, and certified organic crops. Photo taken and originally published by Dan Charles/NPR

Allen describes using crop rotations in his various systems as well as hand weeding and herbicides in his organic and conventional fields respectively. He explains that the yields are less in his organic systems, but the revenue per acre is double, because some people prefer to buy organic food:

“I grow varied types of crops to spread my risks. We grow organic because it’s more profitable.

John Callis, a conventional pear farmer in the Sacramento River Delta uses chemicals to control pests in his 700 acre orchard, but not the kind you might expect. The synthetic chemicals he sprays are not insecticides but moth sex hormones called pheromones. He uses an “integrated pest management (IPM) system” to “balance the good guys against the bad guys”. The moth pheromones don’t kill insects, but attract and confuse male moths, so they can’t find females during mating season. As a result, the pear-munching codling moth larvae are not produced during the part of the year when the fruit is developing. John directs me to a University of California-Davis webpage outlining similar IPM systems for dozens of crops. Many of these systems include the use of synthetic chemicals, but reflect a major goal of organic agriculture, to “optimize the health and productivity of interdependent communities of soil life, plants, animals and people”.


John, Jill, and their sons Jay & Will (from R to L) use an IPM system to grow conventional pears in the Sacramento River Delta. Photo provided by John Callis

As I reflect on my interactions with these farmers and the inaccurate representations in simplistic caricatures floating around the Internet, I consider Wood’s motivation in painting “American Gothic”. According to his biographer Darrell Garwood, Wood passed the house in the painting and “thought it a form of borrowed pretentiousness, a structural absurdity, to put a Gothic-style window in such a flimsy frame house.

The house still stands today. Perhaps Wood misunderstood the structure and the people who lived there as many of us misjudge the motivations and practices of modern farmers.  Given the rising popularity of the food movement, I hope this post inspires the reader to get to know the challenges facing real farmers rather than relying on internet stereotypes or romanticized idealizations.      


Activity: Breeding Vs. Genetic Engineering

Plant breeding and genetic engineering are incredibly useful tools. Like most tools, they serve distinct purposes. Plant breeding randomly combines the genes of two closely related plants. This is useful when both parents have several useful traits. Genetic engineering allows scientists to move specific genes between species. I used the following scenario to demonstrate the precision of genetic engineering as compared to plant breeding to freshmen at San Marin High School:


Two volunteers were selected to be “genetic engineers” and the remaining 15-20 students were “plant breeders”. Each student was given two solo cups, one representing maize (corn) and one representing its wild ancestor teosinte. Each cup contained six Popsicle sticks each representing a gene. The bottoms of the Popsicle sticks were colored green, yellow, or red. The colors represented useful genes, neutral genes (conserved between corn and teosinte), and undesirable genes respectively. Corn had three useful genes and three neutral genes. Teosinte had one useful gene (the disease-resistant trait), two neutral genes, and three undesirable genes.


Students were instructed to “make a cross” between these two species by selecting three Popsicle sticks from each cup. “Genetic engineers” had clear cups and could pick the genes they wanted. “Breeders” had red cups and had to randomly select their genes. The goal was to maximize the number of useful traits and avoid any undesirable traits.

Each of the genetic engineers selected four useful genes and two neutral genes. Breeders ended up with a variety of different combinations. Only one breeder successfully avoided picking any red Popsicle sticks; however, this student still ended up with less total positive/green traits than the genetic engineers.

The students asked what a breeder would do to generate the same optimized crop as the genetic engineers. The “breeder” whose new crop had no undesirable traits put his Popsicle sticks into a new cup and then “back-crossed” it with maize (again randomly selecting three popsicle sticks from each). After two rounds, he still had not managed to generate a variety with as many good traits as the genetic engineers. I then went on to explain that this scenario assumes there are only six genes in corn and that each of those genes acts independently. In fact there are over 30,000 genes and neighboring genes tend to be inherited together.

Creative Commons License
Hands-on Activity: Breeding Vs Genetic Engineering by Jenna E Gallegos is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
Based on a work at

Whatcha gonna do with all that junk-all that junk inside them genes?

Imagine if all the music on itunes was interrupted by blocks of white noise that you had to manually edit out every time you downloaded a song. Makes no sense right? Why would songs be recorded that way? Why not just remove the junk at the source, so you don’t have to waste time and energy?

That’s exactly what scientists wondered when they discovered genetic material known as introns. Genes are regions of DNA that are used as templates to make molecular messages called RNA. RNA provides instructions to make the proteins that determine an organism’s traits. This process, called “gene expression” is the “central dogma” of molecular biology. Before RNA is used to make proteins, large sections called introns are removed. The remaining sections, which actually contain the genetic information, are spliced back together.

Central Dogma

GENE EXPRESSION: In a process called transcription, DNA is used as a template to make an RNA message. Regions of the RNA known as “introns” are cut out, and the remaining pieces are spliced back together to yield mature RNA. The mature RNA message is then used as instructions to build a protein in a process called translation.

Introns, originally called “junk DNA“, are not present in the mature RNA and do not influence the final protein product. So why do cells waste energy, copying introns just to remove them immediately afterwards?

Returning to the music analogy, imagine itunes gives in to complaints and removes the white noise. Customers are surprised to find that suddenly some songs are not downloading as efficiently. Some can only be downloaded a few times per day, others will not download at all, and the most popular songs are hit the hardest

That’s what happens when scientists try to express genes without introns. For many genes, the intronless version does not yield as many copies of RNA. Further, some genes are completely dependent on this “intron-mediated enhancement” or “IME”. Only certain introns exhibit IME, and they tend to be found in the most fundamental genes, those that are expressed all the time.


Certain introns can increase expression of some genes to varying degrees. This figure shows three plant seedlings that all contain a gene that encodes a protein that makes a blue dye. The blue dye gene in the plant in the middle does not contain an intron. In each of the other plants, the blue dye gene contains a different intron. This work was completed by a previous student in our lab and is published in Plant Biotechnology Journal.

IME can increase the expression of genes anywhere from 2 to 20 fold in plants, animals, and fungi. In my lab, we study IME in plants, because introns are routinely used to increase expression of genes in crops from herbicide-tolerant soybeans to nutritionally enhanced rice. Better understanding IME could enable us to design synthetic introns that maximize gene expression potential.

Despite the obvious utility of IME, little is known about the mechanism. What we do know doesn’t fit conventional models of gene expression. For example, in order to exhibit IME, the intron must be very close to the start of the gene. Remarkably, if an IME intron is inserted into a gene that is usually only expressed in certain tissue, it can cause that gene to be expressed everywhere. New data shows that IME can even influence the length of an RNA message and act independent of DNA regions normally thought to be essential for expression.

If you want to dig deeper, my advisor Dr. Alan Rose and I published a review on the topic aptly titled “the enduring mystery of intron-mediated enhancement”. You can access the full-length PDF and a video summary on my publications page.