How to handle corn nematodes
By TOM J. BECHMAN
I still remember the field day some time back when Purdue University pathologists first talked about sudden death syndrome. One farmer walked away from that talk as soon as it started. “I’ve got enough to worry about. I don’t need to know about some new thing that might become a problem.”
The rest, of course, is history. Sudden death syndrome is a perennial problem. Walking away from a potential new problem won’t make it disappear. The newest problem is corn nematode.
The panel from the Indiana Certified Crop Advisers group tackling this issue’s question includes Betsy Bower, agronomist with Ceres Solutions, Terre Haute; Steve Dlugosz, crops consultant for Harvestland Co-op in east-central Indiana; and Bryan Overstreet, Purdue Extension ag educator in Jasper and Pulaski counties.
Key Points
• Five different kinds of nematodes can affect corn in Indiana.
• Symptoms vary and can be confused with other causes.
• The only way to confirm nematodes are present is through soil tests.
Some of my corn doesn’t look very good so far. Could it be nematode damage? What symptoms do I look for?
Bower: Yes, it could be nematode damage. However, the reasons for unhealthy-looking corn early in the season are numerous. Don’t assume it will always be nematodes. Corn nematodes can be found every year in cornfields. It’s only when populations exceed thresholds that damage occurs.
Damage symptoms vary, depending upon species and time of year. There are two basic types — those that feed on root surfaces and those that feed within corn roots. There are several species of each. Needle nematodes, root surface feeders, have high damage potential. They are predominantly found in soils with more than 70% sand. It’s the only nematode that can kill corn. Damage occurs early during cool, wet conditions. Plants are typically yellow and stunted with stubby roots. Symptoms can resemble herbicide injury. Nematodes will seek cooler soil as temperatures warm. Yield loss can still be severe.
Dlugosz: Nematode injury, though uncommon, can cause problems on lighter soils in cool, wet weather. Plants may appear stunted and discolored. Roots, when dug and washed, may appear stunted, stubby and discolored.
Overstreet: Needle, lance, lesion, dagger and root knot nematodes can be found in Indiana. They damage plants by reducing or modifying root mass. Roots serve as food for nematodes.
Bower: Lance and lesion nematodes feed inside the roots. Although they are only considered moderately damaging to corn, populations of each can reach high levels. Corn symptoms and timing of damage from lance nematodes are similar to needle nematodes. However, they can remain active all season long and can affect corn in many different soil types. Lesion nematodes are more damaging in midseason. Symptoms are more nondescript and could be confused with nutrient deficiencies.
Overstreet: If there are visible symptoms from nematodes, they may look like numerous other things. Symptoms are generally in irregular patterns within the field. The only way to tell for sure is to send a soil sample to a nematology laboratory.
Sick and getting sicker: This corn plant shows classic signs of nematode feeding on the roots. That produces sickly-looking aboveground symptoms.
Photos courtesy of Jamal Faghihi, Purdue University Department of Entomology
This article published in the June, 2010 edition of INDIANA PRAIRIE FARMER.
All rights reserved. Copyright Farm Progress Cos. 2010.