What are Plant-Parasitic Nematodes and How to Control Them

Parasitic diseases are a common cause for lawns and gardens to lose their health and vibrance. One of the most common pests that dwell in residential landscapes are nematodes, or worm-like organisms that are beneficial in some cases but harmful to most grasses.

Because nematodes are incredibly small creatures, they are quite difficult to spot and are only visible through the aid of a microscope. With that being said, the symptoms they cause are generally easy to identify, allowing you to make necessary treatments for your lawn and garden. There are also many types of nematodes, but this article will focus on plant-parasitic nematodes, symptoms of infestations and the proper measures to take to prevent and control nematodes.

What are nematodes?

When discussing nematodes that affect plants, nematodes are unsegmented roundworms that live in the soil and feed on plant tissue. They are microscopic in size making it difficult to see them with the naked eye. Certain nematodes can be beneficial for the soil as they feed on bacteria, fungi and other microscopic organisms. There are other nematodes that unfortunately serve no purpose in your lawn and garden other than damaging it.

Some nematodes are ectoparasites, meaning they only feed on the surface of plant tissue while others are endoparasites, meaning they can live inside the host. Additionally, some live above ground while others live below the surface.

The LSU Ag Center States:

“Nematodes that feed on plants can generally be separated into two types. The first type can be found in the above-ground parts of a plant (generally buds or foliage). The summer dwarf and spring dwarf nematodes that attack strawberries are the best examples of these types in the garden. Both cause leaves to be deformed and appear crinkled and distorted. The second type of nematode is generally found to occur in either the soil or roots of plants. Most of our problems are caused by nematodes within this group. The root-knot nematode is the most important and best example of this group. This nematode causes damage to the root system which affects growth and development of many plants in the yard or garden.”

What does a nematode look like?

There are many different types of nematodes, but something they all have in common is their microscopic size, so you can’t really see them. Plant parasitic nematodes can attack the roots, stem, foliage and flowers of plants. All plant parasitic nematodes have stylets, or piercing mouths. Adult nematodes are usually long and slender with sharp mouths that can puncture plant tissue and roots. 

It’s important to know that these nematodes are not the same worms that have the capability to infect the human body and spread disease. However, they do carry viruses and diseases that can be spread throughout various plants.

What do nematodes feed on?

While nematodes can affect nearly all grass types, some species are greater targets than others. The most common grasses that nematodes affect include St. Augustine grass, centipede grass, zoysia grass and bahia grass. Seashore paspalum may also be affected by nematodes, although it’s more tolerant to nematodes than other grass species.

Nematodes also feed on many crops and ornamental plants. 

How do nematodes damage plants?

Before you begin looking for nematode symptoms, it’s important to understand how nematodes affect plants. As with many other lawn pests, plant-parasitic nematodes feed on the plant’s root system. As a result, roots become damaged and cannot properly obtain nutrients and water from the soil. This, in turn, may cause your plants to wilt or your garden to thin out. Depending on the number of nematodes in your lawn, you may notice patches of dead grass that eventually grow larger in size.

Pictured above: Plant roots damage by the root-knot nematode.

How do I identify a nematode problem?

While symptoms of nematodes are often identified from the surface, they are most evident under the soil. Once dug up, you will notice that roots have a short and stubby appearance. Additionally, the roots may look rotten and even cropped off about an inch. The root-knot nematode will also create knots on the roots. To accurately diagnose nematode infestation, you must send a sample of your soil to a local extension agency nematode lab.

How are nematodes sometimes beneficial?

Contrary to popular belief, many nematodes are actually beneficial to lawns and gardens. Because they feed off the eggs and larvae of common insects, they are often used as an organic pest control. 

While nematodes work wonders on a number of pests, most homeowners use nematodes for chinch bugs, ticks, fleas and weevils. Additionally, some homeowners apply nematodes for mole crickets.

Applying beneficial nematodes to your home landscape is a simple process that requires adding water and spraying them to your lawn and garden. When to apply nematodes for chinch bugs and other insects depends on the type of insect you’re targeting, but is generally done in the spring. 

To prevent damage, it’s critical to only apply beneficial nematodes such as a few listed below that will not destroy your grass. Be sure to read through product labels thoroughly to make sure the specific nematodes help with whichever problem you’re having.

Additionally, nematodes can be incredibly beneficial for your soil as they help regulate the populations of other organisms in the soil, mineralize soil nutrients into plant-available forms, provide a food source for other soil organisms and feed on diseases-causing organisms. As they move around in the soil, they distribute bacteria in new places and spread them around, These bacteria can speed up the process of decomposition, which returns carbon to the soil.

In summary, small populations of nematodes have the ability to stimulate root growth. However, high numbers of nematodes can damage roots and aboveground growth. As a result, this makes plants vulnerable to disease and leads to a decreased return of organic material to the soil which eventually lowers soil carbon.

What time of year do nematodes damage lawns?

Most nematode species are active during the warm summer months and can’t penetrate roots at soil temperatures below 64 degrees Fahrenheit. With that being said, there are ways you can reduce nematode injury to fall-planted crops by waiting until soil temperatures have dropped below this temperature.

If you are more concerned with nematodes in your garden or crops, the University of California Agriculture and Natural Resources has a really helpful article on when certain nematodes affect various plants here. 

Although their article states that there are currently no chemical nematicides or soil fumigants available to home gardeners for nematode control in backyard gardens and home landscapes, research has advanced since this article was published and solutions are now available. 

How do I treat a nematode problem?

Cultural Control

Cultural practices for lawns and gardens slightly differ from one another. Some of the best practices for managing nematode damage in home lawns involve reducing other external factors that may stress your lawn so that it can bounce back from nematode damage. Follow our care guides on various grass types for best management practices.

One way to help with nematodes in garden plants is to apply top dressing or some other organic material to the soil to reduce the effect of nematodes. Organic material will increase the soil’s water holding capacity. Nematodes will damage water-stressed plants more, so helping the soil’s water holding capacity lessens these effects. Watering the lawn and garden more may help as well. 

Regularly aerating will help promote a healthy root system and, as a result, help with your plant’s tolerance of nematodes. If the affected areas are located in partial shade, trimming or thinning trees to increase light to turfgrass will greatly build the turfgrass’s ability to withstand nematode damage.

For crops, ornamentals and other garden plants, consider rotating plants to control certain nematodes. This is only helpful for nematode species that have a narrow host range. 

These tips won’t rid your home landscape of nematodes, but it will reduce the damage effects on your plants and lawn.

Although fertilizer doesn’t treat infestations, a proper fertilizer schedule will help your lawn remain strong and endure stress a little better. You might want to consider a fertility program such as Lawnifi®. Lawnifi is a fertilizer program designed to give your lawn nutrients throughout the various seasons of the year. Subscribe to receive seasonal Lawnifi fertilizer boxes throughout the year or purchase each seasonal box individually. You can learn more about Lawnifi by reading Why Use Lawnifi Fertilizer?.

Chemical Control

If nematodes are already damaging your yard, the best approach is to use nematode care products. Certain articles state that there are currently no chemical solutions available to homeowners for nematode control, however, research has advanced since some of these articles were published and solutions are now available. 

One of the best active ingredients for effectively controlling nematodes is Indemnify (active ingredient: fluopyram, which is also a fungicide). Unlike other nematicides, it has very long residual activity and can provide nematode suppression for months after application. 

How do I prevent nematodes?

Identifying nematodes is the first step to managing them. If you haven’t yet identified a nematode problem, there are many preventative measures you may take to reduce their appearance in the future. In most cases, maintaining a healthy lawn or garden is the best way to prevent nematodes from damaging your turfgrass. Proper irrigation and fertilization are excellent ways to minimize stresses on your residential landscape that may result in nematode damage.

Proper maintenance for other garden, plant and ornamentals will also help significantly. However, be sure to use only nematode-free nursery stock for planting. You can also try to use benches raised off the ground and pot plants.

When treating your lawn and garden for nematodes, be sure to continue providing proper care for each. Minimizing other stresses such as drought can reduce the change of nematodes damaging your turfgrass and ornamentals.