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Posted 20 October 2008. PMN Crop News.


Corn Nematodes Threaten Fields Across the Midwest


Syngenta Crop Protection. www.syngentacropprotection-us.com


Are your grower customers seeing lower yields in corn fields that have the ability to produce higher returns? Does their crop show little to no sign of damage or stress? Have they considered corn nematodes as the culprit?

 

While these microscopic, thread-like round worms are invisible to the human eye, corn nematodes can inflict major damage to crops, which can lead to sizable yield losses. In recent years, changing production practices have created an environment conducive to nematode survival, making it especially crucial for growers to understand how these pests can harm their fields and their profits, as well as ways to safeguard against this threat.

Types of Nematodes

Corn can be attacked by at least two dozen species of nematodes. “The most common nematode is the lesion or root-lesion nematode,” said Dr. Terry Niblack, a nematologist at the University of Illinois who has been studying nematodes for about 25 years. All soil types are at risk for the lesion nematode, which is also one of the most damaging corn nematodes. In sandy soils, Niblack notes that some of the most injurious and commonly found corn nematodes are the needle, sting and stubby-root nematodes.

Nematodes are classified into three major categories based on their root-feeding characteristics: endoparasitic nematodes completely enter the host as they feed from within and live within the roots; semi-endoparasitic nematodes can feed from the outside or partially enter the root to feed; and ectoparasitic nematodes feed only from the outside and live mostly in the soil.

A Hidden Pest

Often misdiagnosed and misunderstood, corn nematodes have become a growing problem in the Midwest as a result of changes in production practices. In recent decades, the widespread use of soil-applied organophosphate and carbamate insecticides helped inadvertently suppress corn nematode damage. Now, with the switch to pyrethroid insecticides and the removal of in-furrow insecticides due to the use of transgenic insect-resistant corn, nematode pressure has become more evident as these products lack the ability to suppress nematodes.

Additionally, some nematodes do not respond well to soil disturbance; therefore, the increased trend in no-till and reduced-tillage farming coupled with more corn-on-corn production also has helped provide a more suitable environment for these creatures to thrive.

While all fields can be vulnerable to corn nematodes, many producers still underestimate the problem. “Most farmers do not sample their soil for corn nematodes,” said Niblack, adding that the symptoms of nematode damage are not easily recognized. Some common signs of damage from corn nematodes include chlorosis, reduction in stalk diameter and discoloration, which can mimic other problems such as harsh environmental conditions or herbicide injury. However, more often than not nematode damage may be impacting crop yield even if visual symptoms are not present. The only way to accurately diagnose nematode damage is to collect and analyze soil and root samples. Several universities and labs in the Midwest provide soil sample analysis services for nematode damage. “Growers need to collect samples to accurately find out what nematodes are in their field, that’s the most important step,” Niblack said. For a list of labs that can analyze soil and root samples for nematodes, contact your local university extension office.

Syngenta Seed Care™ recognizes the threat that growers face with corn nematodes and is working to receive registration for a corn seed treatment nematicide. For more information, please contact your Syngenta Seed Care sales representative.