Attack of the corn nematodes

If your cornfield has patches of stunted and poorly growing plants with no obvious cause, nematodes may be the culprit.

Many types of plant-parasitic nematodes attack corn, in all likelihood, for as long as it has been grown as a row crop. In fact, every plant species – with the possible exception of dodder – has at least one nematode parasite, so corn is no different. However, there is a growing concern about the impact of nematodes in corn production and based on some recent changes in this crop’s production, this concern may be justified.

In Michigan, as well as most other states in our region, there are at least eight different types of plant-parasitic nematodes that feed on corn. None produce the national impact of, say, soybean cyst nematode on soybean, but there are some destructive species nevertheless.

The nematode that receives the most attention on corn in Michigan is the corn needle nematode, but it is somewhat limited in its distribution, therefore lessening its impact. Corn needle nematodes are typically confined to fields with coarse textured soils (greater than 70 percent sand) where corn is grown nearly continuously. Symptoms due to its feeding are quite drastic: severely stunted plants and yield losses of 50 bu or more/A. However, corn needle nematodes are usually only found in roughly 10 percent of all corn samples submitted to Diagnostic Services for nematode analyses.

Lesion nematodes are the most frequently detected nematodes on corn as well as most other field crops grown in our state. We find them in roughly 75 percent or more of all corn samples submitted. In general, their impacts in corn production have largely been ignored. In many situations, they do not produce significant yield losses, but since they are so common, they are probably responsible for the highest amount of yield loss due to any of the nematodes on corn in the North Central Region. I read a quote by Greg Tylka, nematologist at Iowa State, who reportedly described nematodes on corn as “yield nibblers,” and I think this is an apt description for lesion nematodes. You can expect them to be present in most agricultural sites, always stealing some yield but often not enough to be noticeable.

Ten to 20 soil samples submitted this spring to Diagnostic Services collected from sites where corn was grown in 2010 in Montcalm County have contained moderate to high population densities of dagger nematodes (50-200/100 cm3 soil). These nematodes are commonly encountered in corn samples (25 to 50 percent of those submitted), but their impact is not well understood. Since these nematodes apparently experienced good overwintering survival, they may reduce yields of crops in 2011.

There is a critical question facing corn producers, and that is, “Should I pay the extra cost on corn seed for nematode control?” Presently, I really don’t know the answer to that question. I have conducted no trials investigating the efficacies of Avicta® and Votivo® for nematode control in corn, so I am left to rely on the information provided by the companies that market the products, grower testimonies or papers published in the scientific literature. For me, the jury is still out. I think it is obvious we need much more information about the roles of nematodes in corn and the effectiveness of these products before I feel confident providing an answer to the question posed.

Growers should engage in on-farm strip trials in order to evaluate these products on corn. To best evaluate the benefits of a product, it is always necessary to leave some untreated strips. Sites should be sampled for nematodes as close to planting as possible, during the growing season and again at harvest, to assess nematode population densities. For problem diagnosis, areas with stunted or poorly growing plants should be sampled for nematodes and the results compared to companion samples collected from healthy areas. It is imperative to obtain as much information as possible in order to make the best, informed decisions.

Growers should monitor their corn crops for patches of stunted and poorly growing plants. If the cause of these problems is not obvious, nematodes may be the culprits. Feeding by plant-parasitic nematodes generally never results in characteristic above ground symptoms. These symptoms typically are similar to those of nutrient deficiencies.

For more information on corn nematodes, consult the Diagnostic Services’ corn nematode factsheet. Online searches will also provide quite a bit of material. For specific questions or concerns, please contact me at 517-432-1333, Angela Tenney at 517-353-8563 or George Bird at 517-353-3890. Currently, there is a $25 fee for a nematode analysis.

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