Nematodes aren’t visible to the naked eye, but you can sometimes see the damage they cause. Tamra Jackson-Ziems, Extension plant pathologist with the University of Nebraska-Lincoln, says now may be the best time to scout for this pest – especially on fields that have sandier soils.
“While plants are small – up to approximately V6 growth stage – [it] may be the best time to sample sandy corn fields for nematodes,” she says. “[Even so], most fields, sandy or not, have a mixture of several nematode species at varying population densities.”
Sampling for nematodes now may make the most sense, when symptomatic areas are more obvious, Jackson-Ziems says. However, it can also be delayed until after harvest when population densities tend to be at their highest.
“Waiting until after harvest to sample may be more convenient for people who plan to collect soil samples for nutrient analyses and can simply collect additional soil for nematode analysis,” she adds.
To collect a proper sample if plants are up to approximately V6 growth stage, start by collecting four to six plants with carefully dug roots, Jackson-Ziems says. Also collect approximately 20 soil cores at a depth of 6″ to 8”, for a total sample size of at least two cups of soil. Refrigerate if possible until shipping. Contact your state’s land-grant university to find out where to ship samples.
“The reliability of your diagnosis depends on the quality of the sample that you submit,” she says. “And, the nematodes in your sample must be alive for an effective analysis.”
It may make the most sense to pull samples from “symptomatic areas,” Jackson-Ziems says. It’s also a good idea to take a second sample from a “nearby apparently healthy area of the field,” she adds.
“Having both samples analyzed for plant parasitic nematodes will allow for comparison of nematode populations and a more definitive conclusion,” she says.
Farmers don't appear to consider nematodes a major problem, at least not according to the results of a recent Pulse poll. Of the nearly 1,000 farmers who responded, only 27% say they used a seed treatment that included nematode protection for the 2016 crop season.
Click here for additional information on nematode physiology, damage symptoms and sampling strategies.