Chemical Control of Weeds

Don Lee Author

09/23/2019 Added

41 Plays

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A summary of why farmers are motivated to control weed populations with chemistry.

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[00:00:00.000]Farmer's Consumers and GMO's Part 1 of Super Weed Evolution.
[00:00:17.000]These are the questions that we want to address with this presentation and we want to talk about why farmers are motivated to control weed populations.
[00:00:29.000]We'll do this presentation in two parts and we'll have a little video intermission between the two.
[00:00:38.000]Let's think about farmers and weeds and why farmers are interested in controlling how weeds grow.
[00:00:46.000]The best place to start, I think, is to compare a weed plant with a crop plant.
[00:00:51.000]Crop plants are domesticated. They're dependent upon the farmer to plant the seeds
[00:00:58.000]in the place where the farmer wants the crop to grow.
[00:01:02.000]They're dependent on the farmer for harvest of the seed.
[00:01:07.000]And then, of course, the farmer benefits from that.
[00:01:10.000]Weed plants have the wild characteristics and the natural ability to complete their life cycle,
[00:01:18.000]to go from seed to seed all on their own.
[00:01:21.000]The plant is a weed, by definition, because it's growing in the same place
[00:01:27.000]at the same time as the crop plant.
[00:01:30.000]So for the farmer, if they're going to be successful in harvesting seeds
[00:01:36.000]from their domesticated crops, they have to minimize the effect of the weed,
[00:01:43.000]and they can do it most effectively if they can prevent the weed
[00:01:48.000]from completing its life cycle, dispersing seeds,
[00:01:51.000]and continuing to be a problem for the farmer in the future.
[00:01:56.000]Weeds and plants, crop plants, want the same thing at the same time,
[00:02:01.000]so their relationship is what biologists call competition.
[00:02:06.000]They're in competition for the water that's available to support plant growth,
[00:02:10.000]the mineral nutrients such as nitrogen, calcium, zinc.
[00:02:16.000]Both crop plants and weed plants will need those
[00:02:19.000]and compete for what's available in the soil.
[00:02:22.000]And then, of course, they compete for the sunlight that they need
[00:02:25.000]to capture light energy.
[00:02:28.000]So farmers are motivated to control weeds
[00:02:31.000]because they compete with their crops
[00:02:33.000]and diminish the productivity of their crops.
[00:02:36.000]And many of you are familiar, even if you're not a farmer,
[00:02:40.000]with the motivation of removing plants that are growing
[00:02:43.000]where you don't want them to grow.
[00:02:45.000]So let's think about why farmers are motivated to use chemistry
[00:02:49.000]to control weeds.
[00:02:51.000]So I think the best way to appreciate that
[00:02:54.000]is to think about the scale or the scope of work
[00:02:58.000]that farmers tend to have.
[00:03:01.000]This might be a fairly typical field of soybeans
[00:03:05.000]that a farmer's responsible for growing in.
[00:03:08.000]And at first glance, or if you were driving by at 70 miles an hour,
[00:03:12.000]you might say, hey, the farmer's not encountering too many problems.
[00:03:16.000]But if we look closely, we can see that there are some weeds here.
[00:03:21.000]These marestail weeds
[00:03:23.000]are able to grow in the same field at the same time.
[00:03:27.000]They're competing with the soybean plant for those resources.
[00:03:33.000]Now, if there's just a few of those weeds,
[00:03:37.000]it might not be a problem worth even addressing for the farmer,
[00:03:42.000]or it might be that they could get out there
[00:03:44.000]and remove a few of those by hand without much problems.
[00:03:50.000]But when you start encountering larger numbers
[00:03:52.000]of weeds that need to be removed to prevent competition,
[00:03:57.000]and you are looking at the magnitude,
[00:04:01.000]the scope of the size of the fields
[00:04:03.000]that farmers are responsible for,
[00:04:05.000]then you can understand why other kinds of weed control,
[00:04:10.000]such as the application of herbicides,
[00:04:13.000]is a motivation that farmers have to be able to use that
[00:04:19.000]to effectively control their weeds
[00:04:21.000]but not damage their crop
[00:04:24.000]because of just the scope of the work
[00:04:26.000]that weed control presents for them every growing season.
[00:04:31.000]So let's think a little bit about chemicals
[00:04:34.000]that have been synthesized by people,
[00:04:38.000]but those chemicals have a very specific
[00:04:41.000]growth controlling capability.
[00:04:45.000]I just listed three chemicals here.
[00:04:47.000]You can see they have some similar features.
[00:04:50.000]We won't worry too much about the chemistry.
[00:04:53.000]One of these chemicals is an antibiotic, amoxicillin,
[00:04:59.000]and this middle chemical is a herbicide that's 2,4-D,
[00:05:05.000]and then there's a growth hormone, human growth hormone.
[00:05:10.000]All can be synthesized or versions of them can be
[00:05:15.000]synthesized by people, and all can be used to control growth.
[00:05:19.000]Antibiotics, of course, are used to control the growth of microorganisms,
[00:05:24.000]and microorganisms that make us sick can be effectively controlled
[00:05:31.000]by the use of antibiotics.
[00:05:32.840]can control the growth of plants, and if it's a selective herbicide and it's safe to use herbicide,
[00:05:42.680]it will have very little or no measurable biological effect on the way animals will grow.
[00:05:49.840]Growth hormone are often selected for and used because they promote the growth of animals.
[00:05:57.860]What all three of these chemicals have in common is that they are currently being used in agriculture or medicine.
[00:06:06.040]They can be used properly and effectively to help us achieve the desired outcome,
[00:06:14.080]or they can be misused if they're not used thoughtfully and properly.
[00:06:18.600]So the herbicide use is what we'll concentrate on here.
[00:06:24.400]And so let's think a little bit about what a herbicide is.
[00:06:27.840]And why it's effective in controlling plants.
[00:06:31.260]So plants have to do a number of biologically successful operations.
[00:06:38.160]And herbicides are chemicals that have been discovered that will disrupt
[00:06:43.280]or block one of these specific operations.
[00:06:48.180]So for example, plants must build all the amino acids that they use
[00:06:52.240]to build their specific proteins.
[00:06:56.100]And there are --
[00:06:57.820]there are herbicides such as glyphosate and glufosinate
[00:07:02.300]that have a chemical structure
[00:07:04.920]that will specifically block the amino acid synthesis process
[00:07:10.220]that happens in plant cells.
[00:07:11.940]So these herbicides are able to disrupt something that happens
[00:07:16.180]in plant cells and the same process doesn't happen
[00:07:19.100]in animal cells.
[00:07:20.180]Okay, plants must conduct photosynthesis.
[00:07:23.720]Okay, that's one of the characteristics
[00:07:25.980]that makes plants unique.
[00:07:27.800]And there are herbicides that are being used
[00:07:31.280]that are pigment blockers.
[00:07:32.600]They disrupt the ability of the plant to make pigments,
[00:07:36.840]chlorophyll molecules that capture light energy
[00:07:41.280]and allow them to photosynthesize.
[00:07:42.920]If the plant cannot do that, they won't be able to survive
[00:07:47.640]and complete their life cycle.
[00:07:49.080]Or just like animals, plants use hormones
[00:07:53.200]to control their growth and some,
[00:07:57.780]herbicides are hormone-like molecules
[00:08:02.100]and disrupt the growth regulating process
[00:08:04.720]that hormones are designed to control.
[00:08:07.080]All right, so herbicides have been discovered
[00:08:09.700]because they specifically disrupt a critical process
[00:08:14.140]in the growth and development of a plant.
[00:08:16.760]As it turns out, once we understand how that process works,
[00:08:22.420]we could take advantage of that understanding
[00:08:24.520]and take advantage
[00:08:27.760]of it with the genetic engineering process.
[00:08:29.900]And so that's a part of the Roundup-resistant crop
[00:08:33.520]or the glyphosate-resistant crop story that we shared earlier.
[00:08:38.120]So the natural ability to withstand life
[00:08:46.460]in a glyphosate-rich environment
[00:08:50.140]was discovered in microorganisms
[00:08:52.560]that were living in a wastewater treatment plant
[00:08:55.480]near a glyphosate manufacturing
[00:08:57.740]facility and geneticists discovered the gene
[00:09:02.960]that was responsible from this microorganism
[00:09:07.180]that encoded a protein that gave them that resistance.
[00:09:10.660]The protein was actually the EPSPS protein,
[00:09:14.380]a protein involved in amino acid synthesis in the microbes.
[00:09:17.500]The microbial version of that was resistant to the glyphosate.
[00:09:22.400]So they can modify that gene,
[00:09:24.720]introduce it into soybean cells growing on a petri
[00:09:27.720]dish, clone plants from that petri dish and those plants possessed in every one of their
[00:09:34.440]cells this bacterial gene modified so that it could be expressed in plant cells.
[00:09:41.680]Once you have those plants and that gene is a part of their chromosomes, they can pass
[00:09:45.360]it on, you could be using that plant as a plant breeder to pass the glyphosate resistance
[00:09:52.180]trait from parents to offspring and develop new varieties that would
[00:09:57.700]grow in the presence of the glyphosate herbicide.
[00:10:02.940]So the crop plant is resistant to the herbicide but the weeds growing near it are not resistant
[00:10:10.740]to the herbicide.
[00:10:12.000]You have a very effective herbicide technology that you can use to control weed growth.
[00:10:19.400]So the ability to transfer the gene for this EPSPS enzyme from the microbe to the plant
[00:10:27.680]gave farmers a technology option that made them even more motivated to use glyphosate
[00:10:34.300]herbicide to control weeds in their fields.
[00:10:38.180]So let's take a little break then.
[00:10:41.540]We've talked about farmer motivation to control weeds and why controlling weeds with chemicals
[00:10:49.260]we call herbicides is an important tool for farmers today and we'll come back and finish
[00:10:57.220]our discussion.
[00:10:57.660]In part two.
[00:10:59.040]Thank you.

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Chemical Control of Weeds

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