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0:38

On a languid damp July morning,

0:40

I meet weed scientist Aaron Hager.

0:43

outside the old agronomy seed house

0:45

at the University of Illinois

0:47

South Farm. in the

0:50

distance around barns built in

0:52

the early 1900s, designed to

0:54

withstand Midwestern windstorms. It's

0:59

the day after a storm system hundreds of

1:01

miles wide rolled through, churning

1:03

out 80 mile per hour gusts

1:05

and prompting dozens of tornado

1:07

watches and sirens reminiscent of a Cold

1:09

War bomb drill. On

1:11

about 23 million acres, or

1:14

roughly two -thirds of the state, farmers

1:16

grow corn and soybeans with a smattering

1:18

of wheat. They generally spray

1:20

virtually every acre with

1:22

herbicides, says Hager, who was raised

1:25

on a farm in Illinois. But these

1:27

chemicals which allow one

1:29

plant species to live unbothered

1:31

across inconceivably vast spaces

1:33

are no longer stopping all the weeds

1:35

from growing. Since

1:37

the 1980s, more and more plants

1:40

have evolved to become immune to

1:42

the biochemical mechanisms that herbicides leverage

1:44

to kill them. This

1:46

herbicidal resistance threatens

1:48

to decrease yields out of control

1:50

weeds can reduce them by 50 %

1:52

or more. and extreme cases

1:54

can wipe out whole fields. At

1:57

worst, it can even drive farmers out of business.

2:00

It's the agricultural equivalent of

2:02

antibiotic resistance, and it

2:04

keeps getting worse. As

2:06

we drive east from the campus in

2:08

Champaign -Urbana, the twin cities where I

2:10

grew up, we spot a

2:13

soybean field overgrown with dark green

2:15

spiky plants that rise to chest

2:17

height. So, here's the

2:19

problem, Hager says. That's

2:21

all water hemp right there. My guess

2:23

is it's been sprayed at least once, if

2:25

not more than once. Water hemp,

2:27

or amaranthus tuberculatus, which

2:30

can infest just about any kind of

2:32

crop field, grows an inch

2:34

or more a day, and females

2:36

of the species can easily produce

2:38

hundreds of thousands of seeds. Native

2:41

to the Midwest, it has burst forth

2:43

in much greater abundance over the last few

2:45

years, because it has become

2:47

resistant to seven different classes of

2:49

herbicides. Season -long competition

2:51

from water hemp can reduce

2:54

soybean yields by 44 %

2:56

and corn yields by

2:58

15%, according to Purdue University

3:00

Extension. Most farmers

3:02

are still making do. Two different

3:04

groups of herbicides still usually work

3:07

against water hemp, but cases

3:09

of resistance to both are cropping up more

3:11

and more. We're starting to

3:13

see failures, says Kevin Bradley, a

3:15

plant scientist at the University of Missouri,

3:18

who studies weed management. We

3:20

could be in a dangerous situation for sure. Elsewhere,

3:24

the situation is even more grim. We

3:26

really need a fundamental change in weed control

3:28

and we need it quick. Because the

3:30

weeds have caught up to us, says Larry

3:33

Steckel, a professor of plant

3:35

sciences at the University of Tennessee. It's

3:38

come to a pretty critical point. According

3:40

to Ian Heap, a weed scientist

3:42

who runs the international herbicide resistant

3:45

weed database, there have been

3:47

well over 500 unique cases

3:49

of the phenomenon in 273

3:51

weed species and counting. Weeds

3:54

have evolved resistance to

3:56

168 different herbicides and 21

3:58

of the 31 known modes

4:01

of action, which means the

4:03

specific biochemical target or pathway

4:05

a chemical is designed to

4:07

disrupt. Some modes of action

4:09

are shared by many herbicides. One

4:12

of the most wicked weeds in the South,

4:14

one that Plague's Stekal and his colleagues, is

4:16

a rhubarb red -stemmed cousin to

4:19

Waterhemp. known as Palmer

4:21

Amaranth, or Amaranthus

4:23

palmeri. Populations

4:25

of the weeds have been found

4:27

that are impervious to nine different

4:29

classes of herbicides. The plant

4:31

can grow more than two inches a

4:33

day to reach eight feet in height

4:35

and dominate entire fields. Originally

4:37

from the desert southwest, it

4:40

boasts a sturdy root system and

4:42

can withstand droughts. If rainy

4:44

weather or your daughter's wedding prevents you from spraying

4:46

it for a couple of days, You've

4:48

probably missed your chance to control it

4:50

chemically. Palmer Amaranth will

4:52

zero your yield out, Hager

4:55

says. Several other

4:57

weeds, including Italian ryegrass

4:59

and a tumbleweed called cochia,

5:02

are inflicting real pain on the farmers in

5:04

the south and the west, particularly

5:06

in wheat and sugar beet fields. Before

5:10

World War I, farmers generally used

5:12

cultivators such as plows and heros

5:14

to remove weeds and break up

5:16

the ground. or they did it

5:18

by hand, like my mother, who remembers

5:20

hoeing weeds and cornfields as a kid

5:22

growing up on an Indiana farm. That

5:25

changed with the advent of synthetic

5:27

pesticides and herbicides, which farmers

5:29

started using in the 1950s. By

5:32

the 1970s, some of the first

5:34

examples of resistance appeared. By

5:36

the early 1980s, he and

5:39

his colleague, Stephen Powell,

5:41

had discovered populations of ryegrass,

5:43

or lowlyum regitum. that

5:45

were resistant to the most commonly

5:47

used herbicides, known

5:49

as ACCase inhibitors, spreading

5:52

throughout southern Australia. Within

5:54

a few years, this species had

5:56

become resistant to yet another

5:58

class called ALS inhibiting herbicides. The

6:01

problem had just begun. It was

6:03

about to get much worse. In

6:06

the mid to late 1990s, the

6:08

agricultural giant Monsanto, now a part

6:10

of buyer crop science, began

6:12

marketing genetically engineered crops, including

6:14

corn and soybeans, that were

6:16

resistant to the commercial weed killer Roundup,

6:19

the active ingredient of which is

6:21

called glyphosate. Monsanto portrayed

6:23

these Roundup -ready crops

6:25

and the ability to spray whole fields

6:27

with glyphosate as a virtual silver

6:29

bullet for weed control. Glyphosate

6:32

quickly became one of the most

6:34

widely used agricultural chemicals, and

6:36

it remains so today. It was so

6:38

successful, in fact, that research and

6:41

development on other new herbicides

6:43

withered. No major commercial

6:45

herbicide appears likely to hit the market

6:47

anytime soon that could help address

6:49

herbicide resistance on a grand scale. Monsanto

6:53

claimed it was highly unlikely

6:55

that glyphosate -resistant weeds would become

6:57

a problem. There were, of

6:59

course, those who correctly predicted that such

7:01

a thing was inevitable. Among

7:03

them, Jonathan Gressel, a professor

7:05

emeritus at the Weizmann Institute

7:07

of Science in Rehovot, Israel.

7:10

who has been studying herbicides

7:12

since the 1960s. Stanley

7:14

Culpepper, a weed scientist at the

7:16

University of Georgia, confirmed the

7:18

first case of roundup

7:20

resistance in Palmer amaranth in

7:23

2004. Resistance rapidly

7:25

spread. Both Palmer amaranth

7:27

and water hemp produce male

7:29

and female plants, the former of

7:31

which produce pollen that can blow long

7:33

distances on the wind to pollinate the

7:35

latter. This also gives the

7:37

plant a lot of genetic diversity. which

7:40

allows it to evolve faster. All

7:42

the better for herbicide resistance to develop

7:44

and spread. These superweeds

7:46

sowed chaos throughout the

7:48

state. It devastated

7:50

us, Culpeper says, recalling

7:52

the period from 2008 to

7:55

2012 as particularly difficult. We

7:57

were mowing fields down. Herbicide

8:01

resistance is a predictable outcome

8:03

of evolution, explains Patrick

8:05

Trannel. a leader in the field of

8:07

molecular weed science at the University of

8:09

Illinois, whose lab is a few miles

8:11

from the South Farm. When

8:13

you try to kill something, what does it do? It

8:16

tries to not be killed,

8:18

Trannel says. Weeds have

8:20

developed surprising ways to get around

8:22

chemical control. One 2009 study

8:24

published in the Proceedings of

8:26

the National Academy of Sciences

8:28

showed that a mutation in the

8:30

Palmer amaranth genome allowed the

8:32

plant to make more than 150

8:34

copies of the gene that

8:36

glyphosate targets. That kind

8:38

of gene amplification had never

8:40

been reported in plants before,

8:42

says Frank Dian, a weed

8:45

scientist at Colorado State University. Another

8:48

bizarre way resistance can

8:50

arise in that species

8:52

is via structures called

8:54

extrachromosomal circular DNA, strands

8:57

of genetic material including the

8:59

gene target for glyphosate

9:01

that exist outside of nuclear

9:03

chromosomes. This gene can

9:05

be transferred via windblown pollen

9:07

from plants with this adaptation.

9:10

But scientists are increasingly finding

9:12

metabolic resistance in weeds, where

9:15

plants have evolved mechanisms to break

9:17

down just about any foreign

9:19

substance, including a range of herbicides.

9:22

Let's say a given herbicide worked on a

9:24

population of water hemp one year. If

9:27

any plants escape or survive

9:29

and make seeds, their offspring

9:31

could possess metabolic resistance to

9:33

the herbicides used. There

9:35

is evidence of resistance developing to both

9:37

of the chemical groups that have

9:39

replaced or been mixed with Roundup to

9:41

kill this weed. An herbicide

9:44

called Glufosinate and

9:46

a pair of substances known

9:48

as 2 ,4 -D and Dicamba.

9:52

These two would normally kill many

9:54

crops too, but there are now

9:56

millions of acres of corn and

9:58

soy genetically modified to be impervious.

10:00

So essentially the response has been to

10:02

throw more chemicals at the problem. If

10:05

it worked last year, if you have

10:07

metabolic resistance, there's no guarantee it's going

10:09

to work this year, Hager says. Many

10:12

of these herbicides can harm the environment

10:14

and have the potential to harm human

10:17

health, says Nathan Donnelly, the

10:19

Environmental Health Science Director at the

10:21

Center for Biological Diversity, which

10:23

is based in Tucson, Arizona. Periquot,

10:26

for example, is a neurotoxic

10:29

chemical banned in more than

10:31

60 countries. It's been

10:33

linked to conditions like Parkinson's,

10:35

Donnelly says, but it's being

10:37

used more and more in the United

10:39

States. 2 ,4 -D, one

10:41

of the active ingredients in

10:43

Agent Orange, is a potential

10:46

endocrine disruptor, and exposure to

10:48

it is correlated with increased

10:50

risk of various cancers. Glyphosate

10:53

is listed as a probable human

10:55

carcinogen by an agency within

10:57

the World Health Organization and has

10:59

been the subject of tens of thousands

11:01

of lawsuits worth tens of billions. Atrazine

11:05

can stick around in groundwater

11:07

for years and can shrink

11:09

testicles and reduce sperm count

11:11

in certain fish, amphibians, reptiles,

11:13

and mammals. Replacing glyphosate

11:15

with herbicides like 2 ,4 -D

11:17

and dicamba, which are generally

11:19

more toxic, is definitely a step

11:21

in the wrong direction, Donley says. It's

11:25

not just chemicals. Weeds can

11:27

become resistant to any type of control method.

11:29

In a classic example from China, a

11:31

weed called barnyard grass evolved

11:34

over centuries to resemble

11:36

rice and thus evade hand

11:38

-weeding. Because weeds can evolve

11:40

relatively quickly, researchers recommend

11:42

a wide diversity of control tactics.

11:45

Mixing two herbicides with different modes of

11:47

action can sometimes work, though That's

11:49

not the best for the environment or the

11:51

farmer's wallet," Trannel says. Rotating

11:54

the plants that are grown helps, as

11:56

does installing winter cover crops and

11:58

above all, not using the same herbicide

12:00

in the same way every year. Fundamentally,

12:02

the solution is to not focus

12:05

solely on herbicides for weed management,

12:07

says Michael Owen, a weed

12:09

scientist and emeritus professor at Iowa

12:11

State University. And that

12:13

presents a major, major issue for the

12:15

farmer. and the current state of

12:17

American farms, he adds. Farms

12:21

have ballooned in size over the last couple

12:23

of decades as a result of rural

12:25

flight, labor costs and the advent

12:27

of chemicals and genetically modified

12:29

crops that allowed farmers to quickly

12:31

apply herbicides over massive areas to

12:34

control weeds. This has

12:36

led to a kind of sinister simplification

12:38

in terms of crop diversity, weed

12:40

control practices and the like, and

12:43

the weeds have adjusted. On

12:45

the one hand, it's understandable that farmers often

12:47

do the cheapest thing they can to

12:49

control weeds, to get them through the year.

12:52

But resistance is a medium to long

12:54

-term problem running up against a

12:56

system of short -term thinking and incentives,

12:58

says Katie Densman, a

13:01

rural sociologist also at

13:03

Iowa State University. Her

13:05

studies have shown that farmers are generally

13:07

informed and worried about herbicide resistance, but

13:10

are constrained by a variety of factors

13:12

that prevent them from really heading it

13:14

off. The farm is too big

13:16

to economically control weeds without spraying

13:18

in a single shot, some farmers

13:20

say, while others lack the

13:22

labor, financing, or time. Agriculture

13:25

needs to embrace the diversity of

13:27

weed control practices, Owen says, but

13:30

that's much easier said than done.

13:33

We're too narrow -visioned, focusing on

13:35

herbicides as the solution, says

13:37

Steven Fenimore, a

13:39

weed scientist with the University of

13:41

California Davis, based in Salinas,

13:44

California. Fenimore specializes

13:46

in vegetables for which there are

13:48

few herbicide options, and there

13:50

are fewer still for organic growers,

13:52

so innovation is necessary.

13:56

He developed a prototype that injects steam

13:58

into the ground, killing weeds within

14:00

several inches of the entry point. This

14:03

has proved around 90 % effective, and

14:05

he's used it in fields growing lettuce,

14:07

carrots, and onions. But it

14:09

is not exactly quick. It takes

14:11

two or three days to treat a

14:13

10 -acre block. Many other

14:15

non -chemical means of control are

14:17

gaining traction in vegetables and other

14:19

high -value crops. Eventually, if

14:21

the economics and logistics work out, these

14:24

could catch on in row crops, those

14:26

planted in rows that can be

14:28

tilled by machinery. A company

14:30

called Carbon Robotics, for example,

14:33

produces an AI -driven system called

14:35

the laser weeder that, as

14:37

the name implies, uses lasers

14:39

to kill weeds. It is

14:41

designed to pilot itself up and down

14:43

crop rows, recognizing unwanted plants

14:45

and vaporizing them with one

14:47

of its 30 lasers. Laser

14:50

weeders are now active in at least 17

14:52

states according to the company. You

14:54

can also shock weeds by using

14:56

electricity, and several apparatuses designed

14:58

to do so are commercially available

15:00

in the United States and Europe. A

15:03

typical design involves the use of

15:05

a height -adjustable copper boom that zaps

15:07

weeds it touches. The most

15:09

obvious downside with this method is that the

15:11

weeds usually have to be taller than the

15:13

crop. By the time the

15:16

weeds have grown that high, they've probably

15:18

already caused a decline in yield. Weed

15:22

seed destructors are another promising

15:24

option. These devices, commonly

15:26

used in Australia, and

15:28

catching on a bit in places like

15:30

the Pacific Northwest, grind up

15:32

and kill the seeds of weeds as wheat

15:34

is harvested. An Israeli company

15:36

called Weed Out hatched

15:38

a system to irradiate and

15:40

sterilize the pollen of Palmer

15:42

amaranth plants and then release

15:45

it into fields. This

15:47

way, female plants receive the sterile

15:49

pollen and fail to produce

15:51

viable seeds. I'm very excited about

15:53

this as a long -term way to

15:55

reduce the seed bank and to manage

15:57

these weeds without having to spray an

15:59

herbicide, Owen says. Weed

16:01

out is currently testing its approach in corn,

16:03

soybean, and sugar beet fields in the

16:05

U .S. and working to get EPA

16:08

approval. It recently secured $8

16:10

million in funding to scale up.

16:13

In general, AI -driven rigs and precision

16:15

spraying are very likely to

16:17

eventually reduce herbicide use, says Stephen

16:19

Duke, who studies herbicides at

16:21

the University of Mississippi. Eventually,

16:24

I expect we'll see robotic weeding and

16:26

AI -driven spray rigs taking over. But

16:29

he expects that to take a while on

16:31

crops like soybeans and corn, since it

16:33

is economically difficult to invest

16:35

a lot of money intending

16:37

such low -value agronomic crops

16:39

planted across such vast areas. A

16:42

handful of startups are pursuing new types

16:45

of herbicides based on natural products

16:47

found in fungi or used by plants

16:49

to compete with one another. But

16:51

none of these promise to be ready for

16:53

market anytime soon. Some

16:56

of the most successful tools for

16:58

preventing resistance are not exactly

17:00

high -tech. That much is clear

17:02

from the presentations at the Aurora Farm

17:04

Field Day. organized by Cornell

17:06

University just north of its campus

17:08

in Ithaca, New York. For

17:10

example, one of the most important

17:12

things farmers can do to prevent the

17:14

spread of weed seeds is to clean out

17:17

their combines after harvest, especially

17:19

if they're buying or using equipment from

17:21

another state, says Lynn

17:23

Sineski, an assistant professor and

17:25

weed scientist at Cornell. Combines

17:28

are believed to have already introduced Palmer

17:30

Amaranth into the state, she says. There

17:33

are now at least five populations in

17:35

New York. Another classic

17:37

approach is crop rotation. Switching

17:40

between crops with different life

17:42

cycles, management practices, and growth

17:44

patterns is a mainstay of

17:46

agriculture. And it helps prevent

17:48

weeds from becoming accustomed to one cropping

17:50

system. Yet another option is

17:52

to put in a winter cover crop that

17:54

helps prevent weeds from getting established. We're

17:57

not going to solve weed problems with

17:59

chemicals alone, Susneski says. That

18:02

means we have to start pursuing these

18:04

kinds of straightforward practices. It's

18:07

an especially important point to hammer home

18:09

in places like New York State where the

18:11

problem isn't yet top of mind. That's

18:13

in part because the state isn't dominated

18:16

by monocultures the way the Midwest

18:18

is, and it has a more diverse

18:20

patchwork of land use. But

18:22

it's not immune to the issue. Resistance

18:24

has arrived and threatens to blow up, says

18:27

Veepan Kumar, also a weed

18:29

expert at Cornell. We have

18:31

to do everything we can to prevent this," Kumar

18:33

says. My role is to educate people

18:35

that this is coming and we have to

18:37

be ready. You were

18:40

listening to MIT Technology Review, where

18:42

Douglas Maine writes, the weeds are

18:44

winning. This article was published

18:46

on the 10th of October 2024

18:49

and was read by Sam Scholl for

18:51

NOAA.