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July 2016

Nematodes

THE INVISIBLE CROP KILLER

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You've probably never even seen any of these animals – even though they are estimated to account for around 80 % of all individual multicellular animals on our planet. Yet the damage plant-parasitic nematodes do to crops worldwide is staggering. These little beasts destroy around 12 % of global crop production worth around $ 100 billion a year. The voracious crop pests we are referring to – nematodes (or eelworms) – are a big concern for soybean, cotton and corn growers in countries like the United States and Brazil.

In Brief:

  • 10–15 % of global crop production damaged by nematodes
  • Soybean cyst nematode No. 1 yield robber in U.S.
  • Key research into integrated chemical and biological crop solution

Ancient animals

Nematodes have been around for around a billion years, but in contrast to other invertebrates very few of them have been fossilized. The oldest nematode fossils, some 120–135 million years old, were found in amber containing insects. Nematode parasites were known to affect humans in ancient times. The first description of a zooparasitic nematode is recorded in Chinese scientific literature way back in 2700 BC and the “fiery serpent” referred to in the Bible (Numbers 21, 6–9) as the scourge of the people of Israel on their escape from captivity in Egypt is reckoned to have been the guinea worm nematode.

Ubiquitous presence

The first scientific report of a plant-parasitic nematode was in 1743. That was in wheat. The root-knot nematode found on cucumber roots was identified in 1855 and by the early 20th century, plant nematodes had been subject to widespread study. One of the most famous nematode quotes comes from the pioneering researcher Nathan A. Cobb in 1914: “If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable: we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes.”

Nematodes have a virtually ubiquitous presence on our planet and can survive even in extreme conditions. The vast numbers of nematodes – several million individuals per m2 – and biomasses of 1–100 kg/ha are one reason for their ecological success. Though generally small or minute, with species of the genus Greeffiella Cobb less than 0.1 mm in length, nematodes can also be several meters long, e.g., the species that lives in the placenta of the sperm whale. Nematode life cycles vary considerably, but they can be as short as three weeks. In such cases multiple generations may attack a plant during a single crop season.

Crop losses worldwide

The damage caused by nematodes varies from crop to crop but averages 10–15 % and is estimated to add up to around US$ 100 billion* a year. In specific crops harvest losses can be as high as 50 %, and nematodes pose a serious threat to a wide range of crops ranging from tomatoes, potatoes and grapes to the broad-acre crops soybean, corn and cotton. The latter three and the world’s top two agro-economies, the United States and Brazil, are the focus of this article.

Unidentified threat

Despite the crop damage caused by nematodes, until recently most farmers knew little about them or chose to ignore them since they are more or less invisible. Gregory Ginisty, Senior Product Manager Bayer SeedGrowth, explains: “Soybean growers in the U.S. saw the damage done but related it to other diseases or pests. What they didn't see, they didn't want to believe was a problem.” Yet the crop losses due to nematodes are huge. Gregory Ginisty: “Nematodes are the number one yield robber in U.S. soybean production. The soybean cyst nematode (SCN), which has been documented in every soybean-growing state, accounted for around 120 million bushels of yield loss in 2014, which added up to a revenue loss of some $ 1 billion. SCN can cut yields by up to 30 % without any visual signs of a problem.” Ironically, U.S. soybean growers were partly responsible for importing the SCN. Back in the 19th century, they began importing soil that contained rhizobia, the beneficial symbiotic bacteria that supplies soybean plants with much-needed nitrogen. Unfortunately, the bacteria-rich soil imported from Asia also contained the SCN pathogen.

Why SCN is so serious

SCN is by far the most threatening nematode species for U.S. soybean farmers, accounting for three times the crop losses caused by the next most dangerous pest. It is widely present and spreading fast. When SCN enters a soybean plant to feed, it damages the roots and deprives the plant of water and nutrients. Even more serious is the fact that the puncture wounds generated by SCN allow diseases to enter the roots. Of these diseases the fungal sudden death syndrome (SDS) is the most deadly. Thus, SCN infestation can result in much worse devastation through SDS. Together, SCN and SDS accounted for around 180 million bushels of yield loss in U.S. soybean production in 2014.

Developing innovative solutions

Bayer was one of the first companies to recognize the severity of the nematode problem and initiated research projects at facilities around the world to develop innovative crop protection solutions.

Invisible enemy in Brazil

Just like in the U.S., many farmers and researchers in Brazil didn't realize that the damage being done to crops was due to nematodes. Instead, they mainly attributed it to other causes. But given the size and economic significance of the agricultural sector to the Brazilian economy, the consequences were serious. Brazil is the world's No. 1 soybean producer, for example, and grows soybeans on 34 million ha. “There are no cultivated plants potentially free of all nematode species, and they can damage 5–35 % of growing areas,” says Siegfrid Baumann, Bayer SeedGrowth manager in Brazil. “Although the extent of crop losses does depend on a farmer's cultivation methods, nematodes represent an extremely serious threat to our country's agricultural production – not just with soybeans but also with cotton, corn, sugar cane, dry beans, coffee, rice and wheat. But before we can effectively tackle the problem, we have to educate farmers about the invisible enemy that is causing so much damage.” When Bayer specialists started trials with a newly developed insecticidal seed treatment about ten years ago, they noticed that CropStar™ also acted as a nematicide. Since its label extension to soybeans and cotton in 2010, CropStar has been effective as a seed-applied insecticide and nematicide – where farmers have used it. But Siegfrid and his colleagues know additional measures are still needed to raise awareness of the nematode problem.

Monitoring nematode damage

To monitor the damage caused by nematodes across the vast expanses of Brazil's agricultural land, Bayer has developed an aerial monitoring service known as Drone CropStar. The aerial photos Drone CropStar takes of, for example, soybean or corn fields reveal the lighter areas where the crop has been damaged. “Since 2012 we have intensified soil sampling and surveys to identify key areas with nematode problems,” Siegfrid says. “When we cross-reference data collected from soil analysis with aerial images made by the drone, we are able to identify the incidence of outbreaks and then work on managing and controlling the pest.” Drone CropStar was launched at the 32nd Brazilian Congress of Nematology in June 2015 and is currently awaiting authorization from Brazil's Civil Aviation Agency for widespread deployment. Siegfrid expects it to be operating commercially by the start of the next soy season in October 2016.
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Drone CropStar shows Nematode damage in Brazil

Bayer's nematode research

For decades, only a few nematicide innovations have been brought to market and many existing solutions have faced severe restrictions due to toxicological or environmental risks and concerns. So Bayer is now focusing its research on innovative solutions, as Dr. Jürgen Benting, a Bayer researcher specializing in nematodes, explains: “We are focusing on complementary innovative approaches in new environmentally favorable chemicals, biologicals, traits and breeding. For example, we screen as many as 100,000 small-molecule compounds a year for nematicidal efficacy before going on to greenhouse testing and, ultimately, field trials on the few substances that are left.

One innovative chemical solution, fluopyram, showed impressive broad-spectrum nematicidal potential at very low rates. This was confirmed in subsequent field trials in the U.S., Italy and South Africa as well as in laboratories and greenhouses in Germany. Marc Rist, another Bayer nematode specialist, explains how the active ingredient fluopyram works: “By preventing the formation of adenosine triphosphate molecules, or ATP for short, fluopyram interrupts the nematodes’ energy supply with the result that they become paralyzed and finally die.” But fluopyram, which is marketed as Velum™, COPeO and Verango™, is only one player in Bayer's complementary approach to tackling the nematode problem.
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The VOTiVO effect: Bacterial colonization on primary roots of corn seedlings.

Bayer's research and development work on chemical and biological crop protection products is complemented by its own research into traits to combat SCN and by cooperative research to breed nematode-resistant vegetable varieties. These strategies are delivering best-in-class integrated crop solutions to tackle, in particular, the plant-parasitic root knot and cyst nematodes that are damaging crops all over the world. Ironically enough, those invisible crop killers are now being defeated in part by biological agents such BioAct that are equally invisible to the naked eye. But soybean, corn or cotton growers in the U.S. and Brazil are not much concerned about how the invisible threat from nematodes is tackled. They just want solutions. And Bayer is supplying them.

THE SOYBEAN CYST NEMATODE (SCN)

Dr. Gregory L. Tylka, a professor at Iowa State University, explains why the SCN is so dangerous: “It's the most difficult plant-parasitic nematode because of its unique biology. For example, an adult SCN male is too small and transparent to be seen by the naked eye, and with a lifecycle of as little as 3½ weeks in summer, there can be 3–4 generations of SCNs during the growing season.” What's more, an adult female SCN can produce over 200 eggs during her short life and those eggs can survive for more than ten years if the soil conditions are favorable for survival. Dr. Tylka estimates that 80 % of the U.S. soybean-growing areas are infected with SCN. One traditional SCN management option, Dr. Tylka says, is to grow non-host crops, e.g., corn. This method reduces the SCN population by up to 50 % in the first year but becomes less effective in subsequent years. The other traditional method is to grow SCN-resistant soybean varieties. But with the SCN-resistant soybean breeding line PI 88788 accounting for around 98 % of all SCN-resistant varieties in the U.S., Dr. Tylka reports a growing resistance problem. For him the most interesting SCN management option is the nematode-protectant seed treatments that have become available in the past 5–10 years.
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