Weeds outsmarting humans, ruining crops

Opinion

Hey there, time traveller!
This article was published 24/08/2019 (2229 days ago), so information in it may no longer be current.

People can argue until the cows come home whether plants actually have “feelings”, but there is no denying they are pretty smart.

If you’ve ever watched a sunflower field over the course of the day, you’ll notice the heads face east to greet the sunrise in the morning and rotate to the west as the sun sets at the end of the day.

The why and how of this was uncovered in 2016 by California researchers who reported that the plants are motivated by the need to attract pollinators, which are attracted to warmer flowers.

A circadian clock guides their movement, and although the plants remain rooted in place, the east side of the stem grows during the day, pushing the heads towards the west. The west side of the stem grows at night, rotating the head back towards the east.

That’s pretty intelligent for a plant that has no brain.

Scientists have only recently completed mapping the genome of wheat, one of the world’s most important food crops and one which has a ridiculously complex genetic makeup.

Wheat as we know it is actually a combination of three grasses that mixed together thousands of years ago. It has five times the DNA of the human genome and it has so far stumped efforts to manipulate it through hybridization.

You could make the case that some plants are even smarter than humans because of their ability to relatively rapidly overcome our attempts to control them.

Weeds are gradually but steadily gaining the upper hand over herbicides.

Take Palmer amaranth for example, named “most troublesome weed” by the Weed Society of America in 2017 because of its ever-expanding reach and hardiness.

It has now developed resistance to eight modes of herbicide control, including glyphosate (also known as Roundup). Just a few short years after crop-protection companies released stacked herbicide applications — such as glyphosate plus 2,4-D, or glyphosate plus dicamba — some plants are no longer responding to those treatments either.

Palmer amaranth has continued to spread out across the U.S., and was recently located dangerously close to Manitoba in North Dakota, where farmers and weed scientists have been quick to pounce on it and pull it out by hand to keep it from going to seed.

One Palmer amaranth plant can produce more than one million seeds, and its highly competitive nature (full-grown plants have the height and spread of a Christmas tree) means it can choke yields by 80 per cent or more.

Tall waterhemp is another weed moving northward that has developed resistance to multiple herbicides. It was found in four Manitoba fields this summer, prompting extension weed scientists to issue an alert for farmers to be on the lookout.

Also highly competitive and prolific, one plant can produce half a million seeds. Waterhemp is an unwelcome addition to the growing roster of herbicide-resistant weeds already cutting into yields on Prairie farms.

Palmer amaranth and waterhemp are somewhat unusual in that they produce both male and female plants that cross-pollinate. Many other weed species have male and female flowers on the same plant. Being dioecious means these plants are more prone to outcrossing and genetic diversity, which can speed up the development of herbicide-resistant populations.

Researchers at the University of Illinois are now trying to identify the pathways to genetically modify the male plants so they would pass their “maleness” on to all offspring. “Ultimately, all plants in a given population would become male, reproduction would cease, and populations would crash,” they say in a release.

“It’s important to emphasize that we are not at the point of releasing genetically modified waterhemp and Palmer. We are doing basic research that could inform how we could do that,” said Pat Tranel, a crop science professor at the University of Illinois.

However, he cautioned that even if they are successful, this should only be one of several control strategies.

The reason weeds got the upper hand on us in the first place is our mistaken assumption that we’re smart — and they’re not.

Laura Rance is vice-president of content for Glacier FarmMedia. She can be reached at lrance@farmmedia.com.