Facts about Nematodes

Nematodes are a fact of life whether you grow corn or soybeans or other crops.

Today, in my opinion, nematodes are one agronomic issue growers don’t know enough about. Did you know that 4 out of 5 creatures on planet earth are nematodes? Here are some other interesting facts about nematodes.

What are nematodes? Nematodes are tiny, colorless, threadlike, unsegmented roundworms but aren’t related to earthworms. Some types of nematodes like hookworms, roundworms, and pinworms attack man as well as animals. There are several dozen species that attack plant roots, as well as a few that injure stems and leaves. These plant-feeding nematodes live in the soil, and most are too small (0.2 – 0.4 mm) to be easily seen with the naked eye.

How do they damage plants? Nematodes feed on or inside plant roots using needle-like mouthparts (called stylets) for piercing and sucking. Affected plants have trouble absorbing enough water and nutrient and become much more vulnerable to soil-borne fungal and bacterial diseases.

How serious is the damage? Heavy infestations can lower crop yields by 30-80 percent. However, yield losses can occur from nematode damage with no visual symptomology on the above ground plant.

How do nematodes spread? Nematodes reproduce by eggs, and life cycles of some types can be as short as 18-21 days in warm soils. Although a typical nematode will move less than half a meter during its life, they are easily spread by soil carried on tools, feet, and transplants or by water runoff from a field.

What crops are most affected? Nearly all crops are susceptible to some type of nematode and corn and soybean are no exception.

Soybean Cyst Nematode: Without question, soybean cyst nematode (SCN) remains the most critical yield-limiting threat to soybeans and I believe that yield loss is likely to increase in the future. Many of you may remember years ago when we took soil samples to check SCN egg counts. We have not had to do this for years because the seed industry began incorporating the PI88788 source of SCN resistance into their soybeans lines.

However, it is now well documented that overreliance on PI88788 as the major source of SCN resistance has weakened its effectiveness as soybean cyst nematode populations continue to evolve. (for more information: http://ilsoyadvisor.com/disease-management/2017/june/combating-scn-weakening-of-pi-88788-resistance/) Another source of resistance is Peking, but this source is not widely available in commercial varieties and is not immune to some of the performance issues we’ve seen with PI8878. Unfortunately, there does not appear to be a new source of genetic resistance for this pest on the near horizon. That is why I feel that SCN needs to be “on our radar” once again.

Management is Key: Like many of you, I was excited when I heard about NemaStrike. I have been following the research results on PI88788 for a few years, so I knew there was a need for increased focus on nematode management and I was glad there was a new product coming that could potentially help with this agronomic need.

However, Monsanto ran into an unforeseen situation with this product and voluntarily removed it from the market. (For more on this announcement go to: https://www.agweb.com/article/monsanto-pulls-nemastrike-for-skin-irritation-issues-naa-sonja-begemann/) I commend Monsanto for this decision as I feel that it was the right thing to do. My hope is that this NemaStrike situation gets resolved and we can move forward with this product in 2019. Just in case this NemaStrike situation does not get resolved, I feel we should be planning for what our best management practices are for dealing with soybean cyst nematodes in 2018 and beyond.

Best Management Practices for SCN

1. Sample – Although we can safely assume that most fields in Illinois that have had soybeans recently also host SCN, sampling for eggs is the best way to determine how bad the problem is. This will also help you understand how the population may be changing over time.
2. Plant resistant soybean varieties – Most SCN management discussions start with SCN resistant soybean varieties as the #1 way to manage SCN… and I agree. However, as we have already discussed, the major source of SCN resistant, PI88788 is no longer as effective as it once was, so while we still need to be planting SCN resistant soybean varieties, I would not rely on this alone for SCN management.
3. Crop Rotation – Rotating to a non-host crop like corn can help reduce SCN populations, but unless you plant corn for several years in a row, the SCN numbers may not be reduced as much as we desire. Also, it appears soybean acres are on the increase, so we may not see as much corn on corn as we have in past. While this is an important practice for many reasons, I see crop rotation as something we already do in Illinois.
4. Controlling winter annual weeds – There is conclusive evidence that certain winter annual weed species are a host for soybean cyst nematodes which means allowing these weeds to survive can increase your populations of this pest. If you are in a no-till or strip trill system and having issues with winter annuals, I would recommend controlling these weeds with a fall herbicide treatment like Autumn Super. (visit https://www.cropscience.bayer.us/products/herbicides/autumn-super)
5. Seed Treatments – This is the where Bayer offers some solutions that can be easily implemented WITH the SCN resistant soybean varieties:
   1. ILeVO – Besides providing protection from Sudden Death Syndrome, ILeVO provides broad-spectrum nematode protection in the seed zone. Complementing nematode-resistant soybeans with ILeVO adds another level of protection that results in reduced nematode damage and increased yield potential.
   2. Poncho/VOTiVO – For the best in soybean protection, pair ILeVO with Poncho/VOTiVO for unmatched control of the SDS fungus, nematodes and insects. We already discussed ILeVO’s nematode protection in the seed zone and Poncho has been proven as the market leading seed applied insecticide for control of secondary pests like white grubs, wireworms and seed corn maggots. But let’s not forget about the nematode protection provided by VOTiVO. Poncho/VOTiVO employs a biological mode of action with a unique bacteria strain that lives and grows with young roots, creating a living barrier that prevents nematodes from causing damage. See Poncho/VOTiVO soybean trial data.

Here is an actual picture of a root taken with a microscope. The black part in lower right is the root showing the root hairs. The yellow area outside the root is the VOTiVO spores. You can clearly see the nematodes (roundworms) that are being kept from doing damage. This clearly shows how VOTiVO creates a living barrier to protect the roots. If you would like to learn more about the value of Poncho/VOTiVO please go to: https://www.cropscience.bayer.us/products/seedgrowth/poncho-votivo/faq#phcontent_10_divAccordion

SCN Coalition – Round Two: Many of you may remember the SCN Coalition from the late 1990s, an organization formed to increase knowledge about SCN and how best to manage this pest. Recently, a second SCN Coalition has been launched with a diverse group of experts, ranging from university scientists, extension specialists, and ag company representatives. Due to the many challenges associated with managing SCN today, their goal is again to raise awareness about this serious pest and provide timely information for growers. I highly encourage everyone to visit their website and take advantage of the resources they have to offer: https://www.thescncoalition.com/