Protecting Crops with Fungicides
Article originally from American Chemistry Magazine
Just like people and animals, plants can become ill. Fungi, bacteria, and viruses can quickly stunt their growth. Fungal diseases, in particular, represent a major problem and can cause very serious damage.
A fungal disease infects a plant in much the same way as bacteria and fungi can cause diseases in people. Most gardeners who have grown roses will be familiar with black spots that that can appear on the leaves; these are signs of disease caused by a fungus.
When many people hear the word ‘fungus,’ they think of a toadstool in the woods, but what they may see growing above the ground is just one tiny component. The larger component by far is the mycelium, a thread-like meshwork below the ground.
With plant fungi, this meshwork grows on the leaves or sometimes even in the plant itself. It feeds on organic substances in the plant, which then makes the plant ill or diseased. In some cases, when the plant cannot function effectively, it will die.
Plants diseased from a fungal attack are a scourge to not only hobby gardeners, but also the agricultural industry. Plant diseases can seriously damage the production of foodstuffs. According to industry estimates, more than 40 percent of crop yields that are theoretically achievable are lost because of plant diseases, bacteria, and environmental impact (such as drought). In response to such problems, researchers develop new fungicides.
Different approaches
Fungicides are classified by the way they work. Some affect the growth of the fungus; others stop the fungus from producing the energy it needs to live; and still others activate the plant’s defense mechanisms to make it more fungus-resistant.
BASF’s F500 fungicide, for example, belongs to the strobilurin group. It blocks the transport of electrons in the fungus’ mitochondria. In this way, the supply of energy to the fungus is inhibited, so it perishes. Given this molecular approach, a single fungicide can function well against a range of different plant diseases in a wide array of cultivated plants or crops.
F500 also works as a sort of tonic or vitamin for a plant. It can help the plant survive certain stresses, such as low temperatures or the dryness of a drought. It tends to confer a darker green, healthier color to the plant. All of these factors can add to the overall growth of the plant and optimize the yield from the farmer’s fields.
Nevertheless, the aim today of new fungicide development is not to cure sick plants, but rather to prevent them from becoming ill in the first place by acting like a protective shield.
Getting such a substance to absorb into the leaves and into the plant itself is a major challenge, however, because plants inherently try to protect themselves from such forces and have developed a corresponding barrier. The key will be to use surfactants, much like those in washing compounds and detergents, to enable a drop of a fungicide to quickly penetrate the plant and not just fall off the leaf or be washed away by rain.
“We’re working intensively with colleagues from polymer research and researchers dealing with surface-active substances, with which we’re able to influence the moistening or surface behavior,” says Dr. Matthias Bratz, Senior Research Manager in Formulation Development at BASF. “In fact, it’s even conceivable that knowledge we’ve gained in the spray paint industry could be applied. Or we can find synergies in areas like construction chemicals or super-absorbers in baby diapers. All of these could ultimately be used in fungicides for plant protection.”
Regional issues
Soybean fields in the U.S.
are seeing more fungicide
applications following a
recent rust fungus scare.
Fungicides especially represent a large percentage of the plant protection products sold in central Europe due to the damp climate, crops sown very closely together, and plant monocultures, all of which facilitate fungal attacks. Other agricultural regions around the world have different conditions and farmers have tended to think of the Americas as suffering fewer fungal diseases. Today, however, U.S. farmers are becoming more aware of problems.
“In 2008, we estimate about 25 percent of corn and soybeans received a single application of fungicide,” says Dr. Amber Shirley at BASF. “A lot of that was driven by the scare of soybean rust fungus a few years ago, especially in the south. A lot of farmers started using fungicides and seeing benefits. Wheat is a more traditional fungicide market, with treatment on demand, driven by weather conditions and green quality—but after the issue of soybean rust, farmers started looking at fungicides and other major row crops, like corn, and it went from about 7,000 acres being treated to almost 10 million acres in 2008.”
Soybean rust is already a major problem in Latin America.
“Brazil is the second largest producer of soybeans and Argentina is the third largest,” says Marco-Antonio Tavares-Rodrigues at BASF Brazil. “Soybean rust can cause up to 90 percent of yield losses if there is no control. You can imagine the importance for the whole of society and government. We can affirm it is more serious than otherfungus diseases. Latin America has more area to increase agriculture in the future, especially in Brazil, so fungicides are getting more important day by day.”
Another example is stem rust, a wheat disease that comes in many varieties. It weakens plants dramatically and can even lead to complete crop failure. One new, extremely dangerous variety of stem rust called Ug99 (so named because it was first found in Uganda) is now threatening harvests in southwest and central Asia.
BASF is working with the International Center for Agricultural Research in the Dry Areas (ICARDA) in Syria to develop a fungicidal program that can control this emerging disease, which is spreading to the northeast. It has already reached Iran and could also spread into India and Pakistan.
Environmentally friendlier
Major row crops, including
corn are now receiving better
protection through fungicide
applications.
The development and use of fungicides pose not only food policy issues, but also environmental issues. Effective substances must provide anti-fungal properties while remaining completely harmless to beneficial insects, for example. Bees, earthworms, and even predatory mites play important roles in plant development and should not be affected in any way.
This is also true for the soil in which the plants grow. If a fungicide can be broken down by natural processes after its work is done, none of it will remain in the ground.
Article adapted from a BASF podcast, “Plant Health—Fit with Fungicides”