Know your nematodes

Published on: 17:19PM Jun 01, 2010
David Long
Here’s a quick overview of the types of nematodes (microscopic, thread-like worms) most likely lurking in your fields – and their symptoms. They could be stealing more yield than you realize…
Root-knot nematodes are the most widespread, infecting corn, cotton and soybeans. Root-knot nematodes feed on the inside of roots as immature larvae. Their secretions cause plant cells at the feeding site to enlarge and produce visible galls on the roots, which absorb plant resources and are vulnerable to other infections.

nematodes are the second most widespread species and affect both cotton and soybeans, making them an increasing threat to Southern growers. They are primarily spread by cultivation. Reniform nematodes partially embed themselves inside roots. After infection, a permanent feeding site forms and leads to a rapid nematode build-up. Plant nutrients are absorbed, causing dark, stunted root systems with few feeder roots. While soybean crops are highly susceptible to reniform nematodes, the problem is often difficult to diagnose and confused with seedling disease or potassium deficiency.

nematodes feed on the outside of the root, but they eventually embed themselves either partially or completely within the root system. Typically, only moderate damage is caused by infestations of this species. Symptoms may include stunting, yellowing of the leaves, darkened roots and uneven growth in the field row. Roots usually bunch together near the soil surface and exhibit a hairy or fibrous appearance. With lance nematodes, root development and nodule development also may be poor.
Stubby-root nematodes feed on the external portion of the growing root tip. Stubby-root nematodes do not usually kill soybean plants, but the severe stunting they cause can lead to considerable yield loss. Symptoms vary but can include stunting, poor stand and reduced feeder roots. After swelling, roots may appear abbreviated or “stubby” looking, preventing them from acquiring adequate water and nutrients for the soybean plant. Stubby-root nematodes usually thrive in sandy soil environments.

nematodes are more ectoparastic nematode species than any other type, meaning they feed on roots from outside. Most soybean fields have at least a small population of stunt nematodes.
Sting nematodes inject a toxic enzyme into the roots of their host while feeding, resulting in significant damage, yield loss and even plant death. Sting nematodes are found almost exclusively in soils with sand content of 80 percent or higher and thrive best in irrigated cropland where there is a constant supply of moisture.