Nematode management
Stephen R. Koenning and Pawel Wiatrak
Nematodes are round worms that reside in the soil. A few species actively attack the roots of plants and may cause yield losses. Often times plant-parasitic nematodes provide a route of entry for pathogenic fungi and bacteria to enter the plant.
Nematodes attack corn roots, thereby limiting their development and restricting the uptake of water and nutrients. Thus, affected plants are stunted and appear deficient of nutrients. Since nematodes do not occur at a uniform population density throughout the field, stunted plants likewise are not uniformly distributed. They often appear in roughly circular areas in the field.
Nematode damage occurs most often when the preplant densities of certain nematodes are high and corn seedlings get off to a slow start because of unfavorable growing conditions. Damage to corn from plant-parasitic nematodes is most severe in the coastal plain area.
Nematodes
Stubby-root (Paratrichodorus minor). The stubby-root nematode does not enter the roots of corn plants, but remains outside the roots and feeds on the growing root tips. Their feeding prevents the further development of the root tip, resulting in short, stunted or stubby roots. The damage to the root system by stubby-root nematodes resembles that caused by several herbicides.
A plant heavily parasitized with these nematodes is stunted, turns yellow, often exhibits magnesium deficiency, and produces a small ear. Since these nematodes are so widespread in the coastal plain area, they may very well be the most damaging nematodes on corn in North and South Carolina.
Sting (Belonolaimus longicaudatus sp.). The sting nematode feeds on roots from the outside without penetrating or becoming attached to roots. They feed at root tips and along the sides of succulent roots. Injured roots show blackened, sunken dead areas along the root and at the root tip. These areas may girdle the root causing it to die. Sometimes the damage done to young plants is quite severe and infected plants may obtain a height of only 8 to 10 inches. Sting nematode is found in soils that contain at least 80 percent sand. This nematode, especially when combined with the stubby-root nematode, causes severe yield losses.
Columbia lance (Hoplolaimus columbus). The Columbia lance nematode can be damaging to corn, especially if numbers are high and poor conditions for early corn growth occur. The Columbia lance nematode is damaging to corn, whereas a related species of lance nematode, Hoplolaimus galeatus, does not generally affect corn. Currently, the Columbia lance nematode is restricted to sandy soils, whereas the common lance nematode (Hoplolaimus galeatus) is found in many parts of the state. Lance nematodes feed on the root surface but may also penetrate the root system causing internal damage. Columbia lance nematode can be extremely damaging to cotton and soybean, but usually causes only slight-to-moderate damage on corn.
Root-knot and Lesion (Meloidogyne and Pratylenchus spp.). Most species of root-knot and lesion nematodes will reproduce on corn. Ordinarily, corn is very tolerant of these nematodes, but may be damaged if populations are very high.
Nematode management
In order to determine whether or not a field should be treated with a nematicide to control nematodes, a soil sample should be collected in September-November. Samples can be submitted through the county agent to the Clemson University Agricultural Services Laboratory. Soil cores collected from the corn root zone need to be taken in a zig-zag pattern across the field and mixed in a bucket. Each sample should cover 5 to10 acres, and sections with different crop histories should be sampled separately. The nematode thresholds are shown in Table 1.
Where the population density is high enough to justify treatment, a grower can expect an increase of about 20 to 25 bushels per acre. Nematodes are controlled by use of a nematicide, rotation, and crop destruction.
Table 1. The probability of nematode damage to corn.
Nematode |
Number of Nematodes per Pint of Soil (fall count) |
||
Slight |
Moderate |
High |
|
Root-knot nematodes: |
0 to 4,900 0 to 4,900 |
5,000+ 5,000+ |
|
Lesion nematode (Pratylenchus scribneri) |
0to 490 0 to 490 |
500+ 500+ |
|
Stubby-root nematode (Paratrichodorus minor) |
0 to 10 |
20 to 190 |
200+ |
Ring nematode (Criconemella spp.) |
no problem |
||
Sting nematode (Belonolaimus longicaudatus) |
0* |
0* |
0* |
Lance nematode (Hoplolaimus galeatus) |
no problem |
||
Columbia lance nematode (H. Columbus) |
0 to 490 |
500+ |
|
* Any detectable number can pose a serious problem.