If you pull up a dying plant and find bulb-like knots on the roots, you might have an infestation of root-knot nematodes.
You can’t see these microscopic pests without a microscope, making early detection nearly impossible. They quickly take ahold of plants and infect the roots in no time. The treatment options are minimal, so getting rid of them is difficult.
If you think you have parasitic nematodes in your garden, keep reading to find out what you can do to help your plants.
What We’ll Discuss
What are Root-Knot Nematodes?
A quick look at their name might tell you that these pests infest the roots of your plant. Nematodes are a form of roundworm, and there are over 25,000 different species. Most of them are beneficial and cause no problems, but some are harmful and dangerous to your garden.
Nematodes are split into two groups: predatory and parasitic. Predator nematodes are the ones you want to have; they seek out and attack other garden pests, like squash vine borers and cutworms. These are your friends.
Root knot nematodes are in the parasitic category. It’s impossible to see these pests with your naked-eye; they’re microscopic, which makes spotting them impossible. They attack living plant matter and eat it. Since you can’t see them before they cause damage, gardeners typically don’t discover an infestation until it’s advanced.
Nematodes only live in the soil; you won’t see them on leaves. They’re fairly common; if they attack a large plant, like a tree, they won’t bother it much. But if they infect a smaller plant like a pea vine, it spells disaster.
These pests attack a large range of food crops, shrubs, trees, and more. Most parasitic nematodes are opportunistic, but some seek out their favorite snack.
Root-Knot Nematode Lifecycle
It’s important to understand the lifecycle of these nematodes, but it’s complicated and broken into several phases.
In the beginning, an adult root-knot nematode leaves behind a gelatinous mass on the root system of the plant it infects. This is where it lays its eggs. One adult nematode lays up to 1,000 eggs – isn’t that crazy? It’s why they’re able to multiple at such quick rates.
Now the egg is the embryonic stage, and it’s when the pest goes through the first of its juvenile phases. At first, the embryo starts to eat the egg that encapsulates it; they don’t hatch. They eat their way out, and by the time it’s out of the egg, it enters the second phase, which is when they become a problem for your plants.
During the second stage, nematodes start to eat through the roots of the plant. This causes the development of root galls, which look like large, bulb-like masses. These form because the plant is trying its best to heal the root system. Unfortunately, nematodes continue to eat through the roots.
Then, the juvenile nematodes bury themselves into the galls, and there they move through the third and fourth stage. After that, the nematodes emerge as adults. At this point, the cycle starts over as the adults lay eggs.
The Plants that Root-Knot Nematodes Eat
Nematodes only eat living plant material, and they only attack the roots rather than above-ground plant parts. If your fruits have holes in them, it isn’t caused by these pests.
It’s impossible to list all of the plants that they like to eat; if it’s there, chances are they’re going to take a bite. Some of the plants that most commonly are impacted by these pests include:
- African Violets
- Banana Trees
- Beans
- Carrots
- Citrus Trees
- Cucumbers
- Eggplants
- Hops
- Lettuce
- Lilacs
- Okra
- Olives
- Onions
- Peas
- Peach Trees
- Peanuts
- Pear Trees
- Peppers
- Plum Trees
- Potatoes
- Pumpkins
- Raspberry Bushes
- Red Clover
- Squashes
- Strawberries
- Sunflowers
- Tomatoes
- Walnut Trees
- Watermelons
Don’t let this list scare you! There are dozens of nematode-resistant cultivars of each of these plants out there. Take a look at the back of your seed packets to see if you have a resistant type. These handle an infestation much better.
The Signs of a Root-Knot Nematode Infestation
These parasitic nematodes cause a lot of damage to your plants as they chew through the roots and stems. Some signs of an infestation include:
- Unexplained yellowing of the plant
- Stunted growth
- Weak-looking plants
- Vulnerability to plant diseases
How to Prevent Root-Knot Nematodes
When it comes to nematodes, your best bet is to actively use preventative measures to keep them away from your garden. There are several techniques that you can try that work well. If you use a few of these, you should be successful at keeping these pests out of your garden.
Root-knot nematodes are one of the most frustrating types of pests because they’re impossible to see, but they’re causing problems with you realizing! Try some of these preventative measures to stop these pests from finding your garden.
1. Use the Right Fertilizers in Your Soil
Some gardeners swear by adding neem seed meal, crab meal, or oyster shell flour to the soil to prevent nematodes. These are fertilizers, but they’re also soil builders that fight against these pests.
Neem seed meal is a fertilizer made out from the leftovers after making neem oil. It reduces pests naturally, and when it breaks down into your soil, it adds small amounts of nitrogen.
Crab meal brings beneficial microorganisms to your garden that fight off parasitic nematodes. At the same time, this fertilizer strengthens the plant’s cell walls, so they start to resist pests on their own. It’s a great tool to have in your gardening toolkit. Pick some up from the brand Down to Earth at Amazon.
Oyster shell flour is similar to diatomaceous earth, though it’s less effective when it’s wet. It makes the soil less inviting for nematodes to visit.
2. Try Black Walnut Leaves and Hulls
You might know that black walnut leaves and hulls contain a compound called juglone. This compound is an effective killer of root-knot nematodes. The problem is that it also has negative effects on some plants, so you have to be careful when using it.
The best way to use these in your garden is to find some fresh walnut tree leaves or smashed hulls and spread them as a thick layer on your bed.
Keep turning to help it turn into compost, and gradually, the juglone compounds enter the soil. It takes up to six months for the compounds to not be toxic to other plants in your garden. At that point, you can plant in your garden.
Some plants aren’t impacted by juglone, so you can use this technique around them right away without taking the extra steps. These plants include onions, beets, squash, melons, carrots, parsnips, beets, and corn.
3. Try Soil Solarization
Never heard of soil solarization? It’s a fancy word that means you heat up your soil using the sun, but there are some serious considerations before you use this method.
The problem with soil solarization is that it kills everything in your garden – nematodes (predator and parasitic), fungi, bacteria, and beneficial insects. That’s far from a good thing, so if you want to use this method, it needs to be a last resort.
Here’s how you use this method.
- Till the soil deeply and flatten it out well.
- Dampen the soil evenly and put a sheet of clear plastic over the top. Make sure it’s secure and won’t blow off with a big gust of wind.
- Leave this plastic in place throughout the hottest months of the year, typically in the summer, for a minimum of two to three months.
- After you’re doing this, it’s necessary to add beneficial fungi, bacteria, and nematodes back into the soil. You can order these online or check your local garden nursery.
For more detailed info, check out our guide.
4. Plant Resistant Varieties
Look for plants marked with an N on the seed packet. These are resistant varieties; many seed suppliers sell them. If they do contract nematodes, the infestations are typically mild.
5. Crop Rotation and Companion Planting
It’s important to use methods like crop rotation and companion planting to prevent nematodes. Some strains are most selective about the plants that they eat, and marigolds are one of the best companion plants to ward off these pests. Try adding some marigolds throughout your garden beds; these flowers are one of the most beneficial to add to a veggie garden.
Can You Treat a Root-Knot Nematode Infestation?
There are only a few organic gardening solutions to get rid of a root-knot nematode infestation. By the time that gardeners figure out the problem and identify the pests, it’s usually too late to treat the problem.
There are also a few nematicides available, but they’re most often used for commercial agriculture rather than home gardening uses.
Here are two options that you can consider buying to use in your garden.
1. Geraniol Compound
These nematicides are made out of geranium oil. These are the most common select by gardeners; Growers Trust Nematode Control and EcoClear Stop Bugging Me! are two organic options. Both of these use geraniol oil, but Growers Trust uses beneficial bacteria, and EcoClear uses cinnamon oils as well.
2. Quillaja Saponaria Compounds
Try saying quillaja saponaria fast. This is made from the root of the soap bark tree; this type of nematicide uses the saponins from the soap bark tree to dramatically decrease the nematode population. Check your local gardening store to see if you can find an option for you.
3. Azdirachtin Products
Another popular choice is any product that uses azadirachtin extracted from neem oil, such as AzaMax. This product isn’t going to work on serious infestations; it’s best if you, somehow, catch the infestation early. It works against other pests as well, like thrips, aphids, and spider mites.
Aside from a few nematicides, there is no way to get rid of root-knot nematodes in your garden. That’s one of the reasons why these pests are so incredibly frustrating for gardeners.
