Sampling corn fields for nematodes
Plant parasitic nematodes are in every field to some extent, ranging from no obvious crop impact to severe injury and tremendous yield loss. In recent years the soybean cyst nematode has been the focus of much attention as we monitor its spread across Nebraska. In contrast, nematodes are already feeding on corn roots in every field to varying degrees.
There are more than 12 species of corn nematodes with common names such as sting, needle, stubby-root, lance, root-lesion, stunt, dagger, and spiral. The degree of crop injury and yield loss in each field depends on
- which nematode species are present in the field and
- their population densities.
The only way to determine whether nematodes are a potential risk factor or causing damage is by collecting and submitting a sample(s) to a laboratory for plant parasitic nematode analysis.
It’s important to collect, handle, and submit samples appropriately in order to avoid compromising the quality of the sample and reliability of the results of the analysis. Recently, nematologists from several Midwest universities updated guidelines for collecting samples from corn for nematode diagnoses and management recommendations. This article describes the updated recommendations for collecting and submitting samples for corn nematode analysis.
When to Sample for Corn Nematodes
Corn nematode species are diverse and don't cause equal damage. For example, needle and sting nematodes are relatively large and uncommon, but often cause the worst visible injury. Because of their larger size, sting and needle nematodes are only present in fields with at least 80% sand.
They can be hard to detect since they can move down several feet in the soil beneath the reach of traditional soil probes. For that reason, now is the best time to sample sandy corn fields for nematodes while plants are small (up to approximately V6 growth stage). Early in the season these nematodes are expected to be shallow in the soil, feeding on shallow corn roots still mainly in the upper 8-10 inches of the soil profile. Scouting now will increase your chance of capturing them in a routine sample.
Most fields — whether sandy or not sandy — have a mixture of nematode species of varying population densities. Other nematode species affecting corn are not known to travel deeper in the soil and would be included in any late season soil samples. Fields with finer textured soils can be sampled for nematodes almost any time. In finer textured fields, sampling can be done early in the season when symptomatic areas are more obvious, or it can be delayed until after harvest, when nematodes will be at their highest population densities. Often, waiting until after harvest is more convenient if you’re planning to collect soil samples for nutrient analyses and can simply collect additional soil for nematode sampling.