Purpose: To position cotton nematodes within the class of invertebrate worm-like animals and to build awareness of their population distributions and densities in U.S. cotton producing states.
What are Nematodes? Nematodes are a class of invertebrate, worm-like animals ranging in size from microscopic to more than 10 feet in length. Cotton nematodes are mostly microscopic. There are more than 10,000 species of nematodes pre-dating dinosaurs. Their simple structure and organ system differentiate them from other worms.
Cotton nematodes are plant parasitic. They must feed on cotton plants to complete their life cycles. Plant parasitic nematodes can be sedentary (non-moving) or migratory. They can spend their lives inside roots (endo-parasitic) or outside roots (ecto-parasitic), or a combination of both. Like insects, they must molt to increase their size. They generally progress through an egg stage and four juvenile stages (J-1 to J-4) before becoming adults. Some species produce eggs by sexual reproduction, while others do not require males to reproduce.
General symptoms of nematode damage to cotton plants include stunting, yellowed leaves, wilting, and stress. Yield loss may not be very dramatic, and often may be attributed to other causes such as poor nutrition, or lack of water. A physical characteristic of plant parasitic nematodes is a hollow tube (called a stylet) used for feeding. The stylet punctures root cells and withdraws nutrition from the host plant.
Where are Cotton Nematodes Found in the U.S.? Plant parasitic nematodes have been identified in every state where cotton is grown. Certain genera and species are restricted to particular soil types and climatic conditions. Nematodes are generally more prevalent and reach higher population densities in the warmer regions of the Cotton Belt.
What are the Major Cotton Nematode Species? The major species are root-knot, reniform, lance, and sting nematodes. The root-knot nematode is found in most cotton growing areas. The reniform nematode is prevalent from North Carolina to Texas, and the lance and sting nematodes are concentrated in the Southeast.
Root-knot nematode (Meloidogyne incognita). It produces galls on roots that look like knots in a rope. It greatly increases the severity and incidence of Fusarium wilt. This pest is commonly seen in fields with Columbia lance nematode, but it is infrequently seen in the same fields with reniform nematodes.
Reniform nematode (Rotylenchulus reniformis). It is called reniform nematode, because the swollen adult female is kidney, or "reniform" shaped. It can increase the incidence and severity of seedling diseases. This pest is commonly seen in fields with Columbia lance nematode; however it is rarely seen in the same fields with root-knot nematode.
Columbia lance nematode (Hoplolaimus columbus). It is called Columbia lance, because it was first found near Columbia, SC. It may increase the incidence and severity of seedling diseases and Fusarium wilt, but this has not been well documented. This pest is frequently seen in the same fields with either reniform or root-knot nematodes.
Population Distributions and Densities Maps: The following maps show the locations of three major cotton nematodes and their relative population densities in 1995. These maps only show trends in populations of root-knot, reniform, and lance nematodes in 13 states.
For more information, order our free information including Nematode Fact Sheets:
- Root-Knot Nematode Fact Sheet
- Reniform Nematode Fact Sheet
- Lance Nematode Fact Sheet
