Taking an environmentally sensitive approach to pest management
Over the past two years the MU Extension Nematology Lab has received an increasing number of soil samples from corn fields. Most of these soil samples have come from SE Missouri where agriculture is intensive, and the number of deleterious plant-parasitic nematodes are correspondingly numerous and varied in these well worked soils. With the advent of double-cropped potatoes the root-knot nematode (Meloidogyne) has become an increasing problem, even on corn, which is often described as a non-host. Other corn nematodes that have been found in Missouri include stubby root (Paratrichodorus), lesion (Pratylenchus), stunt (Tylenchorhynchus), dagger (Xiphinema), and spiral (Helicotylenchus and Scutellonema).
In 2006, the Missouri Extension Nematology Lab discovered a new species of corn cyst nematode from a sample collected in the NW corner of Tennessee. Th is site is only about 20 miles east of New Madrid County, Missouri and 15 miles south of Mississippi County, Missouri on the east side of the Mississippi River. The problem corn field had a large crescent shaped area of plants which were stunted with yellowing narrowed leaves, poor tasseling and poor ear formation. The exact identification of the cyst nematode recovered from this sample has not yet been determined. Initial greenhouse studies indicated that this new cyst nematode could reproduce on corn but not on soybean.
In 2007, the University of Missouri Plant Protection Program funded a research project designed to survey problem corn fields in the "Delta" counties of southeast Missouri for corn nematodes including the new species of cyst nematode, to conduct a greenhouse host-range study of the newly identifi ed corn cyst nematode species on graminaceous plants, select dicots and a large collection of commercial corn hybrids and to conduct a greenhouse study of life cycle duration and temperature preferences of the newly identified corn cyst nematode.
During the summer of 2007, a total of 35 soil samples with corn roots were collected from symptomatic areas of corn fields in SE Missouri by regional extension specialists. These soil samples were processed for vermiform (worm stage) nematodes and the roots were processed for endo-parasitic nematodes as well as for the presence of cysts. Any cysts found in samples underwent a bioassay on both corn and soybean to check for reproduction of corn cyst and/or soybean cyst nematode.
The new corn cyst nematode was not detected in any of the 35 soil samples.
Fourteen of the 35 samples (40 percent) had no plant parasitic nematodes above the economic threshold (the economic threshold or action threshold is the nematode population level that may cause a economic loss at harvest; it is the point at which action may remediate the potential damage caused by nematodes).
Sixty percent of the corn samples had nematodes above the economic threshold broken down as follows: (some samples had more than one nematode above the threshold)
Although the dagger nematode was found in low numbers; lance, ring, and needle nematodes were not found at all.
No dicotyledons were found to be hosts for this new corn cyst nematode. Of the monocotyledons, tested only corn and goose grass were good hosts (barley did reproduce the nematode equal to the original inoculum).
All the different corn hybrids tested reproduced the nematode from 5 to 28 times the initial inoculum level in 30 days. Commercial hybrids with seed treatments also were good hosts (even better hosts with the treatment washed off).
The corn cysts appear to mature a bit sooner than SCN at 81 degrees Fahrenheit. At day 23 the corn cysts had 86 percent of the egg number compared to day 31 (SCN had only 26 percent).
When inoculated with the same number of eggs, the corn cyst produced more cysts (25 percent) than SCN, the smaller cysts produced less eggs per cyst (33 percent) compared to SCN.
The corn cyst prefers a soil temperature of 81 degrees. At day 28 corn grown with a root temperature of 23 degrees produced corn cyst eggs at a rate of only 3 percent of those grown at 27 degrees.
In a greenhouse study of soil type preference, the corn cyst reproduced best in sandy soil, then clay soil, and least well in loamy soil.
To test how the corn cyst nematode might survive winter temperatures, corn cyst infested soil was buried outdoors for 3 weeks in soil temperatures of 18 degrees to 57 degrees. This soil had a lower reproduction rate (26 percent) compared to infested soil kept at room temperature.
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REVISED: April 6, 2012