AgWeb Online Field Guide - Nematodes
Nematodes belong in a pest category all their own. These microscopic parasites can cause extensive damage to corn and soybean crops by attacking plant roots. Unfortunately, lab testing is needed to determine for certain the presence and type of nematodes.
However, there are symptoms that you can scout for that may indicate the presence of nematodes. Look for stunted, wilted, yellowed or dead plants, and short, stubby roots. See below to learn more about nematodes.
If you suspect you have a nematode problem, contact your local Extension Office for testing.
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Description: Parasite that is visible only under a microscope. Feeds from inside and outside the corn roots.
Timing of damage: Early spring but can be active throughout the season
Type of damage: Plants are yellow and stunted, and roots are stubby and short. These nematodes cause the most damage in sandy soils.
Scouting: A month after planting and before soils warm up, take a sample of the roots and soil. Place root with soil ball in a plastic bag and send to a nematology lab for testing.
Economic threshold: None established.
Description: A small transparent parasite that is visible only under a microscope.
Timing of damage: Mid-season but active throughout growing season
Type of damage: Plant stunting and yellowing and short, stubby roots.
Scouting: Lesion nematodes feed inside the roots, so root samples are necessary. Take samples at midseason and place in a plastic bag to send to a nematology lab. Be careful not to expose samples to high temperatures.
Economic threshold: When nematodes exceed 250 per 100 cubic cm of soil and 1 gram root tissue.
Description: Transparent parasite that measures about ¼" but can only be seen under a microscope.
Timing of damage: V2 to V4
Type of damage: Short stubby roots and yellow stunted plants. Needle nematodes feed on root tips from the outside of the roots.
Scouting: A month after planting and before soils warm up, take a sample of the roots and soil.
Place root with soil ball in a plastic bag and send to a nematology lab for testing.
Economic threshold: One to five nematodes per 100 cubic cm of soil prior to planting.
Root knot nematode
Description: Worm-shaped parasite that is invisible to the naked eye.
Timing of damage: When soil temperatures reach 60°F to 65°F and continues to develop as long as soil temperatures remain above 50°F
Type of damage: Plants will appear stunted, wilted or yellowed, or they will be dead. Roots of infected plants appear swollen or knotted.
Scouting: Dig stunted plants from the edge of the infected area and check for root galls. Take a
soil sample from the root zone and send it to a nematology lab; be sure to keep the soil in the
shade to avoid high temperatures.
Economic threshold: Varies with soil type. Ask nematology lab or local Extension office for guidelines.
Soybean cyst nematode
Description: Roundworm, about 1⁄25" long. Females are usually swollen and can be seen with the naked eye. Yellow to white in color. Larvae are less than 1⁄64" long. Eggs are contained in dead females, which are brown and lemon-shaped and appear as cysts on roots.
Timing of damage: V2 to R6
Type of damage: Plants will appear yellowed and stunted, usually in patches throughout the field.
Scouting: Dig up stunted plants and wash soil off roots by placing in a bucket of water. Check for female nematodes on roots. Then take a soil sample and send to a nematology lab.
Economic threshold: Varies. Ask a nematology lab or local Extension office for guidelines.
Learn more about managing nematodes: