How Corn Nematodes Can Impact Yield Potential

August 10, 2026

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An Overview of Corn Nematodes

  • Corn nematodes can reduce corn yield potential without visible symptoms.
  • Some nematode species feed on the surface of roots (ectoparasitism) while others feed within the roots (endoparasitism).
  • Soil and root samples are required to determine nematode presence and species identification.
  • Depending on the species, the life cycle of corn nematodes can vary from 24 days to an entire season and the number of generations per year can vary from one to five.
  • Weeds can provide an alternate host for some corn nematode species so good weed management is helpful in controlling them.

Potential Corn Yield Loss Due to Nematodes

Estimating the amount of corn yield loss due to nematode infestations can be difficult. Even if a field produced excellent yields, top-end yield potential may have been reduced because nematode feeding restricted nutrient uptake that could have further increased yield potential. The estimated loss of corn yield due to nematodes in the United States averaged about 57.1 million bushels per year from 2020 through 2025, with a range of 34.1 million bushels in 2025 to 75.6 million bushels in 2020.1

Individual nematode species vary in their damage potential. As an example, needle and sting nematodes can cause extreme damage when there is only one nematode per 100 cubic cm (cm3) of soil. Table 1 lists damage threshold estimates for different nematode species. Note, these are damage thresholds only and are NOT calibrated on a response to a nematode control product.

Table 1. Corn Nematodes, Estimated Thresholds, Feeding Site, and Primary Soil Type*

Table shows corn nematodes, their threshold, habitat and primary soil type
TP-2026080601

If corn is growing under very good to excellent environmental conditions, symptoms of nematode feeding may not be apparent even if nematodes are plaguing the crop—setting the stage for hidden yield loss. Below is the compiled list of above- and belowground symptoms caused by corn nematodes. Many of these symptoms can be confused with those caused by other agronomic factors (disease, nutrient deficiency, insects, or herbicide injury).4

Aboveground Signs of Corn Nematode Damage

  • Thin stands
  • Stunted plants
  • Uneven plant height
  • Uneven tasseling
  • Leaf yellowing
  • Small ears and kernels
  • Drought stress (wilting)4
Corn field with brown patches in a field from nematode infestation
Figure 1. Patches in a corn field indicating an infestation of nematodes. Photo courtesy of Tamra Jackson-Ziems, University of Nebraska.

Belowground Signs of Nematode Damage in Corn

  • Swollen or stunted roots (Figure 2)
  • Black or dark brown dead spots on roots (necrotic lesions)
  • Limited fine roots and branches (Figures 3 and 4)4

Corn plant root where the roots have been shortened due to stubby root nematodes
Figure 2. Roots shortened due to stubby root nematode infestation. Photo courtesy of Seminole Crop Consulting, Donalsonville, GA.


Corn plant root that lacks lateral roots from sting nematode damage
Figure 3. Sting nematode damage to corn roots. Note the lack of lateral roots. Picture courtesy of and used with the permission of Clemson University-USDA Cooperative Extension Slide Series, Bugwood.org.


Corn plant root where the roots have been stunted from root knot nematode damage
Figure 4. Root-knot nematode injury. Picture courtesy of Clemson University, USDA Cooperative Extension Slide Series, Bugwood.org.


Sampling the roots and soil is the only way to determine if potentially damaging nematode populations are present in a field. Both soil and root samples are required because some nematodes live within the roots (endoparasites) and others live only in the soil and feed externally on the roots (ectoparasites).

Field history and soil type play a huge role when sampling for nematodes. If a field has a known nematode history, then sampling timing can be dictated by the previously identified species. However, early season sampling is generally recommended because nematodes are more likely to be closer to the surface when soil temperatures are lower. If the field is at least 80% sand, sampling should be conducted prior to the V6 growth stage (six leaves with exposed collars) because sting and needle nematodes can migrate several feet deep into sandy soil as temperature increases. When sampling early (by V6) on any soil type, four to six plants should be dug with roots intact. Collected samples should be representative of 40 acres or less. If nematodes are suspected in identifiable problem areas, soil samples should be collected from the problem and the non-problem areas for comparison.

Sampling Procedures for Corn Nematodes in Sandy Fields

  • Select sample sites. Collected samples should represent an area of no more than 40 acres.
  • Sample the perimeters of large areas suspected to have nematode infestations, not the center of those areas.
  • Collect four to six plants (up to V6 growth stage).
  • The root zone should be probed six to eight inches deep at an angle.
  • About 20 soil core samples should be collected and mixed to get at least a two-cup sample.
  • Double bag soil and plants separately in sealable zipper-top plastic bags.
  • Samples should be handled gently to help avoid damaging nematodes. Nematodes must be alive for proper analysis.
  • Refrigerate samples until shipping.
  • When ready to ship, pack samples in a leak-proof container with soft packing material.
  • Complete a submission form for the respective diagnostic laboratory.
  • Samples should be shipped early in the week. 5

Sampling Procedures for Corn Nematodes in Non-Sandy Soil Type Fields

  • Select sample sites. As with sandy soils, any samples collected should cover an area of 40 acres or less.
  • If nematodes are suspected in identifiable problem areas, soil samples should be collected from the problem and the non-problem area for comparison.
  • If sampling is completed by V6 growth stage, four to six plants should be collected by digging the roots carefully.
  • If sampling after V6, no additional roots are necessary as long as soil cores are collected from the root zone.
  • Follow the same handling and shipping guidelines for collected samples as outlined above.5

Corn Nematode Management

There are two management strategies for damaging nematode populations.

  1. Crop rotation with non-host crops.
  2. Using available soil-applied nematicides to keep the population in check.

There are no rescue treatments available.

Sources

1Sikora, E., Faske, T., Meyer, R., et al. 2026. Corn disease loss estimates from the United States and Ontario, Canada – 2025. Crop Protection Network. https://cropprotectionnetwork.org/publications/corn-disease-loss-estimates-from-the-united-states-and-ontario-canada-2025.
2Tylka, G. 2009. Common corn nematode characteristics. Iowa State University, ICM News. https://crops.extension.iastate.edu/cropnews/2009/08/common-corn-nematode-characteristics
3Davis, R.F., Bertrand, P., Gay, J.D., Baird, R.E., Padgett, G.B., Brown, E.A., Hendrix, F.F., Balsdon, J.A., and Jagdale, G.B. 2026. Guide for interpreting nematode assay results. Circular 834. University of Georgia Extension. https://extension.uga.edu/publications/detail.html?number=C834
4Tylka, G. 2007. Nematodes in corn production: A growing problem? Iowa State University, Integrated Crop Management.
IC-498(1):10–11. https://crops.extension.iastate.edu/encyclopedia/nematodes-corn-production-growing-problem
5Jackson-Ziems, T. 2015. Corn nematode sampling. University of Nebraska–Lincoln, CropWatch. https://cropwatch.unl.edu/corn-nematode-sampling

Additional Resource

Tylka, G. 2009. Quick facts about corn nematodes. Iowa State University, ICM News. https://crops.extension.iastate.edu/cropnews/2009/04/quick-facts-about-corn-nematodes

Web sites verified 07/30/26. 1211_131401



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