What is a nematode?
Unlike with other plant-eating pests, it can be hard to see corn and soybean nematodes with the naked eye. But their impact can be obvious.
Nematodes are a group of microscopic, soil-dwelling, parasitic roundworms that can cause significant damage to corn and soybean crops—ultimately decreasing your yields and profitability.
These organisms will start to feed on roots once planting is finished, which can hinder the plant’s growth. They use their feeding organ (a “stylet”) to pierce the plant and extract nutrients, leaving behind open wounds on the roots. This makes the plant more vulnerable to diseases throughout the growing season.
Signs of an infestation
If you see yellowing or wilting leaves, stunted growth, or decreased yields, it may indicate a corn or soybean nematode infestation. If nutrient and environmental conditions seem fair and you experience any of these symptoms, take soil samples to determine if nematodes are present.
If those samples find nematodes, some simple steps can help eradicate them—for example, crop rotation practices or nematicides. Good crop management and sanitation practices can also stop future infestations.
Nematode soil sampling methods
In order to gain a better understanding of nematode distribution and species, it’s best to take soil samples during the middle of the growing season (V4-V6) when corn and soybean nematodes are most active. Prior to collecting the samples, make sure the soil is neither too wet nor too dry. Use a probe to penetrate the soil at an angle between eight and twelve inches deep, which should be enough to get through the root zone.
Take a minimum of 20 samples from around the edges of the symptomatic plants, including at least two root samples. Place each root and soil sample in individual bags, then in double-bagged containers. If you plan to send the samples the following day, store them in the refrigerator overnight.
For further information on the sampling process, visit your local laboratory or state university extension website.
Sting nematodes commonly occur in coastal regions and the Plains, and have also been known to infest sandy soils in the Corn Belt. Controlling them can be difficult. Their damage to a corn plant’s root system can lead to water deprivation—which can cause the plant to stunt, wilt, or even die.
You can spot lance nematodes in any region and soil type. They have a wide host range and can tolerate many different chemicals, which makes them difficult to manage. These pests feed on roots, creating wounds that can let in diseases and trigger root rot and swelling. As a result, the symptoms of infestation, such as yellowing or dying corn patches, may be similar to those of drought or nutrient deficiency.
Needle nematodes are one of the most destructive species to corn plants. They are only present in sandy soils, and it only takes a few to cause serious damage. They are especially hard to detect, as they are both transparent and microscopic. Once they start feeding on the root tips, they stunt lateral roots and destroy the fibrous root system, leading to yield decreases.
For more information about the various types of corn nematodes, where they can be found, and their mode of action, take a look at Acceleron’s nematode damage/thresholds chart.
More than 100 varieties of nematodes that feed on soybean plant roots have been identified. Of these, only a few are considered to be economically significant, such as soybean cyst, root-knot, lesion, and reniform nematodes.
Soybean cyst nematodes can be highly damaging to soybean plants if they are planted in continuous rotation. These female nematodes are lemon-shaped and white in color. As they mature and infect the plants, they will transform to a tan to brown color. Telltale signs of an infestation include oval and circular patches of stunted growth, wilting, and yellowing within the soybean field.
Root-knot nematodes feed on the roots of soybean plants, leading to enlargement and swelling. If environmental conditions are suitable, female nematodes can lay up to 1,000 eggs. This causes the swelling to form knot-like structures, which then negatively affect the plant’s growth. Symptoms of root-knot nematode infection may include plant stunting, wilting, yellowing, and even premature death.
Lesion nematodes cause damage to soybean plants by breaking open root cells and forming cavities. This allows the nematodes to move inside the cells and feed on healthy tissue, damaging the roots. As a consequence, the plant becomes more vulnerable to diseases, and yields decrease.
Reniform nematodes, found mainly in southern portions of the United States, cause severe yield loss in soybeans and cotton through root damage. You only need a hand lens to identify them, thanks to their distinct, kidney-shaped appearance. If they are present, you will see symptoms of plant stunting and foliage chlorosis. If you suspect reniform nematodes in your fields, you should take soil samples right away to confirm. To minimize their damage, use crop rotation on infected acres the next season.
How to manage nematodes
Unfortunately, corn and soybean nematodes won’t go away without a control method, especially if you’re planting back-to-back soybeans in your field. The best way to tackle a nematode problem is to implement crop rotation, using crops that aren’t a potential host plant. Since corn nematodes have a narrow host range, planting soybeans the following year can help kill off their population—and vice versa. To guarantee effective crop rotation, make sure to remove any weed species during the off-season.
Selecting nematode-tolerant corn hybrids and soybean varieties can also limit the damage nematodes have on your crop. To maximize protection, add a seed treatment. Reach out to your local AgriGold agronomist to talk through options that fit your needs.
If other control methods have failed to manage nematode populations, and the nematode pressure is serious enough, it may be necessary to apply nematicides. These chemicals are both expensive and toxic, so it’s crucial to consult your agronomist before use.
For any questions about how to control plant parasitic corn and soybean nematodes, reach out to your AgriGold agronomist or state university extension website.