As a gardener, there is always another pest, disease, or adverse weather condition right around the corner, but nematodes can be a particularly distressing problem. They’re microscopic, so unlike grubs or larvae, they’re impossible to spot underground. Don’t worry, though, there are simple things you can do to identify and get rid of nematodes in your garden.
What are nematodes?
Nematodes are a type of unsegmented roundworm. Some of these roundworms, called plant-parasitic nematodes, cause damage in agriculture, turfgrass, and home gardens.
How is it that these nematodes wreak so much havoc? Plant-parasitic nematodes have a needle-like, piercing mouthpart called a stylet. This sharp appendage allows them to pierce plant roots and take nutrition from the cells. This action weakens the plant by interfering with the root system’s ability to uptake nutrients and water. In other words, the plant can’t get adequate food or water to nourish itself.
Here are a few common plant-parasitic nematode species that affect home vegetable gardens:
- Cyst nematodes
- Dagger nematodes
- Northern root-knot nematodes
- Reniform nematodes
- Ring nematodes
- Root knot nematodes
- Root lesion nematodes
- Sting nematodes
- Stubby root nematodes
- Stunt nematodes
Note: In Northern and Southern states, the northern root-knot and root-knot nematodes, respectively, are among the most common plant-parasitic nematodes in home gardens. They are both members of the Meloidogyne species.
Other nematodes you may be familiar with are beneficial nematodes. These nematodes are different in that they have no stylet and therefore cannot harm plants. Beneficial nematodes are often used by home gardeners to control pests such as fleas, ticks, borers, thrips, and other unwanted insects.
How to identify nematode damage in your garden
Now that you know how these microscopic critters suck the life out of your plants, how do you know whether you have a nematode problem or if it’s some other problem, like grubs? Here are some things to look for:
- Stunted growth
- Plant decline or poor performance and yield
- Leaf yellowing
- Galls, swelling, or knots on roots (usually from root-knot nematodes)
- Roots that have egg cysts (from the cyst nematode)
It’s good to keep an eye out for these symptoms, but they’re not sufficient for a diagnosis. The plant symptoms from nematode damage mimic many other issues, such as drought stress, insect damage, or disease. Therefore, the only way to identify nematodes is to send a soil sample to a lab.
The nematode test results will include which type(s) of nematodes you have, the population level, and whether treatment is necessary. If treatment is necessary, the test will provide guidelines for control, as well.
Since sampling for nematodes is slightly different from sampling for a standard soil test, go to your state’s Cooperative Extension website for instructions on how to sample for nematodes. Although you can sample for lawn nematodes any time of the year, sampling for nematodes in the garden should be done from August to October, according to Auburn University. This timeframe may vary depending on the crop and where you live.
How to get rid of nematodes in your garden
If nematodes have decimated your vegetable garden, you want them to be gone ASAP. Here are a few ways to reduce nematode populations in your garden.
Solarize the soil
Soil solarization is an effective tool for any garden fighting against a nematode infestation. Here’s how to solarize the soil in your garden:
- Buy a clear plastic tarp: UV stabilized, 1-4 mm polyethylene or PVC
- Till the soil until there are no clumps, debris, or large air pockets.
- Lightly moisten the soil. Leave drip irrigation in the area to maintain moist soil throughout the process.
- Bury the edges of the tarp a few inches deep to prevent displacement.
- Leave the tarp on for four to six weeks in the summer or six to eight weeks in spring or fall. (This is a good rule of thumb for Southern states. In the North, the timetable may be longer.)
The soil needs to reach 140 degrees Fahrenheit to kill weed seeds and nematodes in the top 6-8 inches. It won’t eliminate the nematodes completely, but it will greatly reduce their numbers.
Use a cover crop
Cover crops are simply a crop that will increase organic matter, control weeds, or add beneficial nutrients, among other things. In other words, it’s not a crop you’ll harvest and sell or eat; it’s a crop that builds and rejuvenates the soil in preparation for next season.
Cover crops (aka “green manure” and “living mulch”) are popular with home gardeners and in large-scale farming for their soil-boosting benefits, but they can be beneficial for nematode control as well.
The idea behind cover crops for nematode control is this: By using a poor host or non-host plant, you deprive the nematodes of food which will greatly reduce, though not eliminate, the population. Nematodes don’t move very far in the soil, so if a food source is no longer present in the immediate area, they’ll die fairly quickly. (Cyst nematodes, and others, are exceptions to this rule.)
How long you’ll need to use cover crops depends on the species of nematode in the soil, how many nematodes are present, and the main crop’s level of resistance to that nematode. A nematode soil analysis is necessary to know how many seasons you’ll need to use a cover crop before you can plant a crop again.
Which cover crop is best? Again, it depends on the type of nematode present. Also, different cultivars of the same cover crop species can have widely differing effects on nematode populations. Once you have your nematode test results, don’t hesitate to reach out to the lab or to your local Cooperative Extension Office for advice.
How to prevent nematode damage in your garden
Unfortunately for your garden, nematodes will never go away completely, but there are steps you can take to keep them at a manageable level.
Keep your tools clean
Clean tillers, garden tools, and cultivators between uses. Nematodes that hitch a ride will spread to other areas. Without this kind of “free ride,” nematodes will stay more localized and spread much more slowly.
Choose nematode-resistant varieties
Some vegetable varieties are resistant to certain species of nematodes, such as the problematic root-knot nematode. If you’ve had problems in past years, here are a few examples of plant varieties that resist root-knot nematode damage:
| Plant | Resistant Varieties |
| Bell pepper | Carolina Wonder, Charleston Belle |
| Hot pepper | Carolina Cayenne pepper, Charleston Hot, Mississippi Nemaheart |
| Lima bean | Nemagreen lima beans |
| Snap bean | Bountiful, Contender, Harvester, Kentucky Wonder |
| Southern pea | California Blackeye #5, Hercules, Magnolia Blackeye, Mississippi Shipper, Mississippi Silver, Mississippi Purple, Texas Cream, Zipper Cream |
| Sweet Potato | Bayou Belle, Bonita, Covington, Hernandez, Jewel, Muraski, Red Jewel |
| Tomato, round | Amelia VR F1, Better Boy F1, Celebrity F1, Empire, Italian Goliath, Mr. Ugly, Park’s Whopper, Samurai F1 |
If you have a particular variety of vegetable that’s not resistant to nematodes, plant it every other year (using a resistant variety in the in-between year). This helps to keep nematode numbers in check.
For many more root-knot nematode-resistant vegetable varieties, check out these webpages from the Alabama Cooperative Extension System (ACES) and North Carolina State University (NCSU).
Rotate your crops
Crop rotation is one way to control nematodes that is free and doesn’t take any extra time. To rotate crops is to move susceptible crops (non-resistant varieties) to a different location in the garden each year. Even moving that crop as little as several feet away the next year may be sufficient.
Crop rotation, especially when combined with the other techniques we’ve mentioned, is an effective tool to add to your nematode management tool belt.
Till your heart out
No-till gardeners can skip this section, but for those who love to rev up a tiller each season, listen up. Here are a few reasons tilling your garden at the end of a season will help reduce nematode populations:
- Tilling pulverizes plant roots and stops further nematode reproduction.
- Nematodes die if they get too dry. Tilling brings nematodes up to the surface of the soil where the sun and wind will dry them out and reduce their population.
Give the soil a rest
If you have the space, leave some of your garden area empty, or fallow, for one year. Till the soil every two weeks to keep weeds out (a food source for nematodes) and to expose the nematodes to the dry air and sun. After one year, the nematode level in the soil should be low enough for a successful annual crop.
Keep a healthy garden
Gardening basics are important. By doing all you can to strengthen the plant, it will have a better chance to withstand some stress (from nematodes or anything else) that comes its way.
Fertilize: Get a soil test to ensure you have adequate nutrient levels. If the soil is deficient, follow the soil test’s recommendations for adding nutrients to the soil. Potassium is particularly helpful in minimizing root-knot nematode damage.
Focus on soil health: In addition to reducing nematodes in your garden, do all you can to boost your soil’s health, as well. Adding compost to refresh the soil prior to each new season is a boon to soil health. In addition to adding organic matter and slow-release nutrients, it also functions as a biological control to help keep nematodes in check.
Reduce soil compaction: Whether you have a no-till garden or use a tiller every season, ensure your soil has plenty of pore space to allow air, water, and nutrients to circulate. No-till methods to reduce soil compaction include using cover crops and broadforking. For others, using a tiller is a common way to prep the soil each season.
Water deeply: Frequent watering is a sure-fire way to encourage shallow roots. Water deeply and infrequently so that roots follow water down into the soil profile, growing strong and deep in the process. Drip irrigation is a popular way to water deeply without wasting water (or cash).
Remove the roots: Pull up your spent annuals at the end of each season — roots and all.
A garden restored
To achieve the greatest measure of success managing nematodes in your garden, the best approach is to use as many of these tips as possible. For example, planting resistant varieties will help, but if you also practice crop rotation, use cover crops, and solarize the soil, you should have a much healthier garden.
If nematodes in your garden have taken up all of your time, contact one of Lawn Love’s lawn care pros to keep your lawn green and growing.
Main photo credit: Potato Cyst Nematode | USDA | Flickr | CC BY-SA 2.0
