Stubby-root nematodes belong to the genera Trichodorus and Paratrichodorus, and are soilborne, plant-parasitic roundworms that may cause significant damage in corn. These nematodes are microscopic and cannot be seen with the naked eye. Stubby-root nematodes are ectoparasitic, meaning they feed on plant roots while remaining outside of the root in the soil. This is in contrast to other nematodes such as root-knot (Meloidogyne spp.) and lesion (Pratylenchus spp.) nematodes which feed on plant roots while inside the host root. Stubby-root nematodes feed mostly at root tips which results in the stubby or stunted appearance of the roots. Some species of stubby-root nematode are also capable of vectoring viruses to some crops, most notably tobacco rattle virus to potato.

Detecting stubby-root nematode damage in corn may be difficult because above-ground symptoms often mimic nutrient deficiencies and/or drought stress. When nematode populations are low, symptoms may not be present above ground. When nematode populations are high, aboveground symptoms include stunted or uneven plant growth, leaf chlorosis or yellowing, small ears/kernels, and poor stands. Symptoms may occur in irregularly-shaped patches in an affected field.

Stubby-root nematode causes roots that appear “stubby” or stunted, and which often have brown lesions on the tips. Sometimes the appearance of stubby roots may not be easy to distinguish, but rather an overall reduction in volume of the root system is present, with fewer and shorter secondary roots. A soil sample for nematode assay will aid in accurate diagnosis.

If a corn crop is suspected to be suffering from stubby-root nematodes, plants should be carefully dug up from the soil, taking care to preserve as much of the root system as possible. Roots can be washed in a bucket of water or under running water to remove soil. A visual inspection should included checking the root system for “stubby” or stunted growth. However, this will not indicate the level of nematode pressure in the field. Diagnosis can be confirmed through assessment of soil and root samples for the presence of the nematode by a plant disease diagnostic laboratory or nematode assay laboratory. Soil samples for nematode assay services may be submitted to the North Carolina Department of Agriculture & Consumer Services, Agronomic Services Division (NCDA&CS), Nematode Assay Laboratory, 4300 Reedy Creek Road, Raleigh, NC 27607.

In order to determine nematode pressure, soil samples should be taken from several areas in the affected field. Using a soil probe, collect 20 to 30 soil cores across a 5 acre block, at a depth of 6 to 8 inches from each area using a grid-like or “zig-zag” pattern across the area. Combine soil cores in a clean plastic bucket and remove a smaller portion of soil from this larger sample to submit to the Nematode Assay Laboratory. Detailed sampling instructions can be found at the NCDA&CS Nematode Assay Laboratory sampling guidelines.

Stubby-root nematodes are obligate biotrophs, meaning they require living plant roots to feed and reproduce. Stubby-root nematodes are migratory ectoparasites, meaning they migrate outside of roots and retain a worm-like appearance throughout their life cycle. The life cycle ranges from 16 to 27 days, depending on the particular species and temperature conditions. Female stubby-root nematodes lay eggs that remain in soil until conditions for hatching are present. After eggs hatch, juveniles move through the soil, locating a host root and begin feeding. After juveniles begin feeding, they will molt three times before they become egg-laying adults. Where populations are established in the field, stubby-root nematodes may be found at greater depths in the soil, even below the zone of cultivation (greater than 11 inches).

Corn is a preferred host of stubby-root nematode and it is difficult to manage in corn/soybean rotations, since both crops are susceptible to this nematode. Rotation to a poor- or non-host crop (including tobacco and rye) when possible may reduce soil populations. Maintaining optimal growth conditions (adequate moisture and fertilization) for corn may help support plants that are affected by stubby-root nematode.

Avoiding the introduction of stubby-root nematodes into the field through sanitation procedures is highly beneficial, as they can be extremely difficult to get rid of once populations are established in the field. Careful sanitation by cleaning of equipment moved between fields is an effective way of reducing the spread of lesion nematodes between fields and farms. Sanitize by washing with a solution of 10% household bleach, removing any stuck soil, then rinsing with clean water and drying before moving to unaffected fields or areas.

Another effective management tactic to reduce stubby-root nematode populations within the field is the use of nematicides when economically viable. Pre-plant soil fumigation, at-plant non-fumigant nematicides or seed treatments, can reduce stubby-root nematode population levels to below economic thresholds. Chemical nematicide treatments are summarized in Table 1 and additional information may be found in the North Carolina Agricultural Chemicals Manual.

The NCDA&CS Nematode Assay Lab provides soil detection and diagnostics

The NC State University Plant Disease and Insect Clinic provides diagnostic and control recommendations.

The NC State Extension Plant Pathology portal provides information on crop disease management

The Southeastern US Vegetable Crop Handbook provides information on vegetable disease management

The North Carolina Agricultural Chemicals Manual provides an up-to-date list of chemicals available for control of nematodes and other diseases and pests

This factsheet was prepared by the NC State University Plant Nematology Lab in 2021.