Fact Checker: Is corn 'head high by Fourth of July' thanks to GMOs?

Introduction

'When I was young farmer 'knee high by 4thJuly' indicated good crop. Thx GMO we can now say head high by 4th July'

Source of claim: A July 2 tweet from Iowa Sen. Chuck Grassley's Twitter account.

Analysis

Grassley's tweet, which garnered more than 100 retweets, credits genetically-modified organisms with producing a taller corn crop earlier in the season in recent years compared with when the 82-year-old senator was young.

We will examine if the corn crop is growing more quickly than in the past, and, if so, whether the rate of growth can be attributed to an increased use of genetically-modified crops.

Beth Levine, communications chairman for the senator's office, clarified Grassley's statement, saying that while 'GMOs may not be the only factor in corn growth, advanced breeding and GMOs certainly are a component of plant growth.'

Levine pointed Fact Checker to a Purdue University study analyzing data gathered by the U.S. Department of Agriculture's National Agriculture Statistics Service.

The study showed U.S. corn grain yields were near 160 bushels per acre in 2012, the year the study was published.

In 1953, when Grassley was about 20, the nation's corn yield was about 40 bushels per acre, the study showed.

One of the easiest ways to increase yield is to increase the biomass of a crop, said Mark Licht, an agronomist at Iowa State University. With corn, that typically means taller stalks.

And in recent years, cornstalks have been head-high or taller by Independence Day, he said.

According to the Purdue analysis, a slight yield increase came between 1937 and 1955 when hybrid corn was first adopted. It then more than doubled between 1956 and 1995 with 'a combination of improved genetics, availability of N(itrogen) fertilizer and chemical pesticides, and mechanization.'

'Bt corn,' which is genetically engineered with the bacteria Bacillus thuringiensis to ward off pests, now makes up the majority of corn grown in the United States, according to the USDA. Since the introduction in 1996, yields have increased at their fastest rate since the USDA started measuring in 1866.

But Licht, who studies corn and soybean production and management, said he would not attribute those gains solely to an increased use of the genetically-modified corn.

Licht said introducing transgenic traits — like Bt — into a crop doesn't change its physical appearance, though traditional plant breeding — such as selecting for taller crops — could.

If Grassley's definition of genetically-modified includes traditional breeding, Licht said, the senator's statement would be accurate.

'If he's thinking more along the lines of transgenic traits, probably not so much,' Licht said. ' ... It's more from earlier planting dates and time period and just our regular plant breeding advancement.'

More than half of Iowa's corn was planted by April 28 this year, according to USDA statistician Brian Gallagher. Planting season has inched forward over recent decades, Licht said. But in 1974, when crop progress was first reported by the USDA, most corn was planted around May 8.

'I can go and look at non-GMO corn hybrids that are just as tall as the genetically-modified hybrid,' Licht said. 'I don't want to attribute it to GMOs themselves.'

CONCLUSION

While corn yields have increased greatly since Grassley was a young farmer, taller cornstalks cannot be attributed solely to an increased use of GMOs. Grassley's tweet did not specify the scope of his definition of 'genetically modified' — which could, technically, include traditional selective breeding — but the World Health Organization and the Food and Drug Administration use a working definition of GMO to mean crops with unnaturally engineered DNA. Those corn crops are not taller than non-GMO crops, so we rate Grassley's statement a C.

CRITERIA

The Fact Checker team checks statements made by an Iowa political candidate/office holder or a national candidate/office holder about Iowa, or in advertisements that appear in our market. Claims must be independently verifiable. We give statements grades from A to F based on accuracy and context.

If you spot a claim you think needs checking, email us at factchecker@thegazette.com.

• This Fact Checker was researched and written by Molly Duffy.