Eelworm In Potatoes: what is it and how do I remove or prevent it?

Eelworm is a parasitic nematode that lives in the soil and feeds on plant roots. Its host plants are nightshades and they particularly like potatoes and tomatoes. If you’re growing potatoes, it is extremely important to educate yourself on eelworms.

If you like to grow a lot of potatoes and tomatoes, you’ll definitely want to keep an eye out for eelworm. Once established and thriving, an eelworm infestation can spread through your garden and be a pain to control. 

In this article, I’ll focus on how to spot and prevent eelworm in potatoes. We’ll go over prevention strategies, the eelworm life cycle, and signs to look out for on your crops.  With this, you’ll be able to understand how to prevent and manage any eelworm issues on your potatoes.

What is Eelworm in Potatoes

Eelworm is a tiny worm-like nematode that affects plants in the Solanaceae family, mostly potatoes and tomatoes. There are over 25,000 identified species of nematodes, most of which play an essential role in maintaining healthy soil life by breaking down organic matter. 

So if you’re growing nightshade plants, eelworms will be a parasite that causes more harm to your plants than benefits to the soil. Parasitic nematodes can’t live on their own and eat the roots of potato plants, compromising plant growth.

The good news about eelworms is that they spread through the soil and not through flight (like many other garden pests). This means that you can easily prevent eelworm from spreading through your garden by quarantining the soil and not planting any nightshades for ten years. But more on preventing and controlling eelworm later.

Eelworm Life Cycle

Potato eelworms have a peculiar life cycle. Since these tiny animals live underground, learning about their life cycle will help you understand when to look out for them and how to best prevent them from reproducing.

Eelworms hatch from the swollen dead bodies of last-generation female eelworms called cysts. Each cyst contains hundreds of eggs that will only hatch when they sense a chemical exuded by nightshade roots. Cysts can remain viable in the soil for over ten years and will wait patiently for potato roots to colonize.

Eelworm eggs on the potato plant roots

Once the microscopic worm-like nematodes have emerged from the eggs they puncture plant roots and eat from the inside. This compromises water and nutrient uptake for the plants, slowing or even killing plant growth.

When the eelworm is almost mature, the females swell up and burst through the root’s cell walls, exposing them to the soil. At this point, the males can fertilize female eelworms, which will stay in the soil as potato plants get pulled out.

In order to survive long periods underground, the cysts will dry and harden, protecting the eggs inside. The eelworms will then lay dormant in their eggs until a new batch of potatoes is planted.

From this summary of the eelworm life cycle, we can understand the parasite’s strengths and vulnerabilities. Their main strength is that they can stay alive for over 10 years, but their weakness is that they can only feed on plants in the potato family.

What effect does eelworm have on the crop visually

Eelworms only attack the plant’s roots, so you won’t see obvious signs above the ground like with caterpillar damage. Plants affected by eelworm will have trouble getting energy and nutrients from their compromised roots.

A potato crop will struggle to grow in the presence of eelworm

The first signs of eelworm will be in malnourished-looking plants. Most often, the potato plants will start yellowing from the base up. The leaves will wilt, growth will slow, and your plants will look unhappy. If you can’t identify any other issues like inadequate watering, it’s fairly probable you have potato eelworms.

When you dig up your potatoes, the tubers will be smaller than expected and will often show signs of rotting.

Small populations of potato eelworm won’t have a huge impact on your harvest. In the first years, your plants will look weak and you’ll likely harvest smaller than usual potatoes. Growing potatoes, tomatoes, and eggplants again in the same place makes the eelworm population grow.

The more eelworms you have, the more damage they will cause to your plants. Eventually, after a few years of uncontrolled eelworm reproduction, you won’t be able to harvest a decent potato.

How to identify potato eelworm

The most difficult part of managing a potato eelworm infestation is identifying it. These microscopic organisms are one millimeter at their largest and live underground. If you have a magnifying glass stashed somewhere, now is the time to pull it out.

The first signs of potato eelworm will be that your plant is starting to yellow and wilt from the base. By mid-summer, before your potatoes have had a chance to mature, the plants will look like they’re dying.

You can confirm your hunch at this point by pulling up the plants in late June to July. If you have eelworms, you should be able to see orange or white cysts on the roots with a magnifying glass.

Cysts are female eelworms whose bodies have enlarged with eggs. The cysts can be white, orange or tan in color. If you see the cysts, you have successfully identified potato eelworm.

What causes eelworm in potatoes

Eelworm in potatoes is most commonly caused by bringing in the parasite on soil or seed potatoes. The biggest challenge is that you can’t see them with the naked eye and you’ll have no idea you are bringing them into your garden.

Soil can be brought in on boots, tools, or gifted plants. Or you can get seed potatoes from a friend who doesn’t even realize they had eelworms in their garden.

Maybe you’re moving soil from a flower bed to a potato bed. Potato plants then signal dormant eelworm eggs to hatch, which would have never been a problem for flowers.

There are several ways to get eelworm in your garden without you even noticing. Using gardening best practices when it comes to sterilizing soil and tools, sourcing quality seed potatoes, and avoiding too much soil movement are the best way to prevent eelworm in potatoes.

How do I remove eelworms from my soil

Once you have eelworms in your garden, the eggs will survive up to 10 years before starving. So always practice preventative methods to control any eelworm populations in your soil.

You will likely never fully get rid of eelworms from your soil. You can control their population so they don’t impact your potato harvest too much.

Eelworms will only hatch when they sense there is a host plant growing nearby. So growing potatoes in the same plot will induce any viable eggs to hatch. If you are always rotating where you plant potatoes and tomatoes, you probably won’t even notice that you have eelworms in the soil.

To remove eelworms from your soil you need to be as persistent as they are. Chemical solutions for eelworms aren’t available to home gardeners so your only option is to go the organic route. Crop rotation is your best bet for controlling eelworm populations.

Rotating beds will reduce the exponential growth of eelworms from one generation to the next. Rotating your nightshade plant on a 6-year plan will keep eelworm populations under control.

Even better would be to not plant any nightshades in that bed for at least 10 years.  During that time, you can plant non-nightshade plants that won’t be affected by eelworm. If you do plant potatoes within 10 years, pull the plants out of the ground as soon as possible to minimize the amount of fertilized females who stay behind.

Not sure how to start practicing crop rotation? PSU’s agricultural extension program has a great summary on Planning a Crop Rotation to get you started.

My favorite eelworm control method is to plant a wild nightshade plant to induce the eggs to hatch. Wild nightshades like Solanum sisymbriifolium are resistant to eelworms since the cell walls are too rough for them to penetrate. However, they still put out a chemical that induces hatching. So eelworm eggs hatch, but the nematodes starve to death.

Planting wild nightshades won’t completely eradicate your problem but can be a key point in a well-rounded eelworm-control strategy.

Can I prevent eelworm

As you can imagine from the previous section, eliminating eelworm is not an easy task. The easiest way to get rid of it is to prevent eelworm from parasitizing your garden to begin with.

I love growing potatoes and tomatoes. They are probably what I grow the most in my garden and each year I grow half a dozen varieties of each. However, there are special precautions I must take to prevent eelworm.

Most cases of eelworm happen without the gardener even realizing it. So don’t forget to adopt cultural practices to prevent spreading eelworm to the rest of your garden. Avoid moving soil around and adopt quarantine procedures for the infected area of your garden.

Wash off boots, disinfect tools, and don’t bring in soil from unknown sources. If you suspect you might have brought in eelworms from an outside source, immediately start implementing control strategies.

Eelworms are attracted to their nightshade host plants. Always growing potatoes in the same place is a sure way to foster a thriving population of eelworms. So the best way to prevent eelworm from becoming a problem in your potatoes is to practice crop rotation.

Potato varieties resistant to eelworm

Biodiversity is fantastic and thanks to the natural selection of the strongest crops, potato varieties have emerged which are resistant to eelworm.

Some common eelworm-resistant cultivars include Maris Piper, Accent, Sante, and Valor. Reach out to your local agricultural extension network to find out what eelworm-resistant potato varieties are ideal for your region.

Keep in mind, however, that growing a resistant variety won’t kill eelworms. Females just won’t be able to develop in the roots and only males reach maturity, severely reducing the population. In order to continue suppressing new eelworms, you’ll still need to practice crop rotation.

Summary

Eelworm is one of those annoying problems in the garden. It isn’t dramatic enough to kill everything overnight and you can even grow potatoes successfully with eelworms living in the soil.

Without persistent control though, the eelworm population will get out of control, making it impossible to grow quality potatoes. Preventing and controlling eelworm is essential for preventing it from spreading to the rest of your garden.

Since they live in the soil and attack plant roots, it can take a while for gardeners to even realize that they have eelworm in the garden. As soon as you catch onto the problem, make sure you follow the advice in this article to minimize damage to your crop. Better yet, start following the best practices laid out in this article today.  Preventative methods like crop rotation will minimize or completely prevent the presence of eelworm in your garden. 

Further reading:

https://www.gardenfocused.co.uk/fruitarticles/pest-disease/potato-eelworm.php