Designing the perfect weed killer

Weeds are one of the biggest threats to a farmer’s crop. But it’s bad for the environment and expensive to just spray herbicides everywhere. Researchers are studying the best ways to help farmers.

From planting all the way through the growing season and into harvest, controlling weeds are likely a farmer’s number one challenge. It’s true that insects, drought and storms all create serious problems for farmers. But it’s weeds that are consistently farmer’s number one challenge. That’s because almost half of a farmer’s crop will be lost without weed control.

I saw a good demonstration of the problem in the labs of BASF in Research Triangle Park. Researchers there are constantly creating new herbicides, pesticides and fertilizers to help farmers.

Steve Bowe, the group leader in biology at BASF pulled out three trays; one had palmer amaranth which is one of the most common weeds. The second held cotton and the third held soybeans. The weeds were tiny; perhaps a half inch to one inch tall. The cotton and soybeans were all a few inches tall.

“This is one week after planting and at this point you’d say maybe this isn’t so bad,” said Bowe. “The cotton and soybeans are larger, they’d be able to compete, but it’s amazing how the amaranth can overcome the crop plants.”

Bowe then turns to a table and carries over two pots. Both plants are several feet tall, but one of them is almost one foot taller than the other.

“Six weeks later, if it had to compete with the palmer amaranth, you’re looking at a situation like this and most of the green here is the palmer amaranth,” explained Bowe, “And you can see how much smaller the soy bean plant is and that’s because the weed has the dynamic ability to complete, to fight with that crop plant for sunlight, nutrients and moisture”

Essentially if the crop plant grows taller so will the palmer amaranth, but the weed grows faster and more efficiently and it will eventually out-compete the crop plant. In fact, researchers say that to really eliminate the competition, farmers need to control the weed about one week after planting. Failure to do that will result in crop loss and economic loss. That’s why researchers at BASF spend a lot of time thinking about weeds and weed control—from the size and shape of the drop of the herbicide to the molecules that make up the chemical. It starts with soil.

The United States has 32 different types of soil. Ryan Aldridge showed me a colorful tray with cups filled with different types of soil. “We get used to seeing the soil outside of our window and assume that’s the only kind of soil there is,” explained Aldridge, biologist with BASF. “But some of these are dryer, some are richer, some have a higher iron content, some have a higher PH, some have a lower PH and finally some have a lot of organic matter mixed and some soils don’t have much at all.”

And when you think about it, North Carolina has a variety of soil types. If you start on the coast there is a very sandy soil and then it starts to contain more clay as you move into the Piedmont. The soil gets redder as you move farther west because there is more iron in it. The soil changes again in the mountains.

So why is all of this knowledge about soil important? The amount of organic matter in the soil is going to affect the amount of herbicide needed. That’s because the herbicide tends to bind to the matter in the soil, and if there isn’t much it tends to go deeper.

“What we want to make sure of, is that herbicide is going to stay in the layer where it will effect your weeds, “ said Bowe, holding up on the small cups. “That means we want the herbicide to stay in the top ¼-1/2 inch of soil. We don’t want it to go too far down and effect where your crop is growing, or in a worse case scenario it goes down to ground water.” Researchers test the herbicides in different types of soil so they can understand how far it will move in a sandy soil as opposed to a clay type soil and adjust the application accordingly.”

Then there’s the question of how best to apply the chemical. Researchers use a spray chamber to test different nozzles, chemical mixes, spray pressures and even speeds of how fast the sprayer moves across the plants.

“We’re trying to mimic what goes on in the real world when a farmer is applying product to his crops in the field,” said Doug Findley, as he pressed buttons and watched on the other side of glass screen as the sprayer passed over a tray of crops. “This chamber provides us a lot of flexibility. So we can mimic low volume applications, something like a farmer in Kansas growing wheat or go to higher volume applications like a golf course.”

The goal of all of this research is for a farmer to use just enough chemical to do what is needed and just the right chemical mix for his field. Using too much chemical hurts and environment and the farmer’s wallet.

“We actually spend about 10 years researching a product before bringing something to market,” said Logan Grief, a specialist in technical marketing and produce stewardship with BASF. “And a lot of that time is spent figuring out how the product can be used most effectively but also identifying the safety of the product. We don’t want to bring anything to market that isn’t safe for the environment and also for people.”

 —Frank Graff 

Frank Graff is a producer/reporter with UNC-TV, focusing on Sci NC, a weekly science series. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!