By Pierce Paul, Terry Niblack
A total 425 corn fields were surveyed for plant-parasitic nematodes during the 2013 and 2014 growing seasons. In each year, soil samples were collected from 15-16 fields in each of 28 counties, across 6 soil regions, and nematodes were identified and counted.
The six soil regions sampled
Ten major morphological types were found, with populations ranging from 0 to 1,164 nematodes per 100 cm3 of soil. Spiral, lesion, lance, dagger, stunt, pin, ring, stubby-root, cyst, and tylenchid nematodes were each found in at least one field. Spiral and tylenchid nematodes were the most frequent, being detected in more than 93% of the fields (that is more than 395 out of 425 fields). The lesion nematode, one of the most economically important groups, was detected in 80% of the fields, while the lance, stunt, and pin nematodes were found in approximately 50% of the fields. Some fields had predominantly one type of plant parasitic nematode, while other fields had as many as 9 of the 10 types. More than 85% of the fields had between 4 and 9 different types of plant parasitic nematodes.
Nematode presence and populations varied among soil regions and also among fields under different tillage and crop rotation practices. Dagger and ring nematodes tended to be more common in soil region 6, whereas lance, stunt, stubby-root, and spiral nematodes were more common in soil regions 1, 2, 3, 4, and 5 than in region 6. In addition, one or more types of nematodes tended to reach higher, and potentially more damaging, population levels in soil regions 1, 2, 3, 4, or 5 compared to region 6.
In terms of crop rotational schemes, spiral, lance, and pin nematodes were more common in fields under corn-soybean or corn-soybean-wheat rotation than under continuous corn, while the other types of nematodes were equally present in continuous corn fields as well as fields under 2- or 3-crop rotation. Lance and stubby-root nematodes were more common, and the lance nematode population tended to be higher, in fields under no-till, vertical tillage, and minimum tillage. Nematode populations also varied with soil pH and texture.
As pH increased from 4 to 9, spiral nematode populations also increased, but lance and pin nematode populations decreased. Lance and lesion nematode populations were higher in soil with low silt content. Research in this area will continue and the focus will be to gather data from counties not sampled in 2013 and 2014; to better understand what these nematodes really represent in terms of damage to our corn crop; and to evaluate different strategies for their management if warranted.