Nematodes on Cannabis: How to Spot Root Damage and Get Rid of Them

Nematodes are microscopic roundworms that live in soil, and while most are harmless or even helpful, plant-parasitic species attack cannabis roots, causing wilting, yellowing, root galls and smaller harvests. You keep them in check with healthy soil, crop rotation, soil solarization, beneficial predatory nematodes and, as a last resort, nematicides. If you grow weed, you've probably heard of them, so here's what they are and how they can mess with your grow.

What are nematodes?

Nematodes are microscopic worms that belong to the phylum Nematoda. They're incredibly abundant in nature and show up in all kinds of habitats, from soil to the oceans. Most nematodes are harmless, but some are plant parasites and can do serious damage.

Nematodes that attack plants

When it comes to growing cannabis, the nematodes you care about are phytoparasitic nematodes, meaning the ones that parasitize plants. They can live in the soil and attack plant roots, cannabis roots included.

Signs of nematodes on cannabis plants

Symptoms of a nematode infestation on cannabis plants can vary, but some common signs include:

1. Wilting leaves: Affected plants can wilt, turn yellow and grow poorly because they can't take up nutrients and water properly.
2. Damaged roots: Nematodes feed on plant roots, which can lead to galls or knots forming on them. Those structural changes make it even harder for the plant to absorb nutrients.
3. Lower yields: A serious nematode infestation can significantly cut your cannabis yield, leaving you with smaller, lower-quality harvests.

Types of plant-parasitic nematodes

Plant-parasitic nematodes are grouped by how they behave and how they feed. Some common types that affect plants include:

1. Ectoparasitic nematodes: These feed on the surface of the roots and can cause mechanical damage as they work their way around the root.
2. Migratory endoparasitic nematodes: These get inside the roots and move through the tissue while feeding on the plant's inner cells.
3. Sedentary endoparasitic nematodes: These settle into the roots and form galls or knots where they feed and reproduce.

How to deal with nematodes in a cannabis grow

Managing nematodes in a cannabis grow can be a challenge. A few strategies include:

1. Crop rotation: Switching up what you grow in a given spot can help break the nematodes' life cycle and shrink their population.
2. Healthy soil: Keeping your soil healthy and balanced can strengthen your plants' roots and make them more resistant to nematodes.
3. Beneficial nematodes: Some predatory nematodes are actually good guys and can help keep plant-parasitic nematodes under control. You can add these beneficial nematodes to your soil.
4. Nematicides: In severe cases, you can use specific chemical nematicides, but handle them carefully and follow the directions.

How do you get rid of nematodes?

Controlling nematodes, especially the plant-parasitic kind that damage crops, is key to keeping your plants healthy and productive. Here are some of the strategies and methods used to control them:

1. Crop rotation: Changing what you plant in an area from one season to the next can be an effective strategy. Some nematodes only go after certain plants, so rotating crops breaks their life cycle and cuts off their food supply. That can help bring down nematode populations in the soil.
2. Resistant varieties: Some plant varieties hold up better against nematodes than others. Choosing varieties known for nematode resistance can be an effective preventive move.
3. Healthy soil: Keeping your soil healthy and balanced is essential. Soils rich in organic matter and beneficial microbes help strengthen roots and make plants more resistant to nematodes. Composting and regularly adding organic matter are both good practices.
4. Beneficial nematodes: Some nematodes prey on plant-parasitic nematodes. Introducing beneficial nematodes into the soil can help control the harmful ones, since they feed on the parasites and help bring their numbers down.
5. Soil solarization: Solarization means covering the soil with clear plastic sheeting during the hot months. The sun heats the soil up enough to kill nematodes and other soil-borne pathogens.
6. Nematicides: For severe infestations, you can use specific chemical nematicides. They're designed to kill nematodes or stop them from reproducing. Use them with caution and follow the manufacturer's instructions, though, since some can be toxic to the environment and to people.
7. Good garden hygiene: Simple habits like removing infected plants and disinfecting your garden tools can help stop nematodes from spreading.
8. Monitoring and diagnosis: Check your soil and plants regularly for signs of a nematode infestation. That way you can take preventive or corrective action in time.

What is the nematode life cycle?

Nematodes, also known as roundworms, generally go through a life cycle with five distinct phases:

1. Egg: A nematode's life starts as an egg. Adult females lay the eggs, usually in the soil or inside plant tissue. How long this stage lasts depends on the species and the environment.
2. First-stage juvenile (L1): When the eggs hatch, they release first-stage juveniles (L1). These are tiny and feed on bacteria, fungi or other microorganisms in the soil.
3. Second-stage juvenile (L2) and beyond: L1 juveniles go through several more stages (L2, L3 and so on) as they grow and develop. Each stage brings an increase in the nematode's size and the complexity of its anatomy.
4. Adult: After the juvenile stages, the nematode becomes an adult. The length and number of juvenile stages vary by species. Adults are the reproductive stage and can be male or female.
5. Egg (new cycle): Once nematodes reach adulthood, the females lay eggs and a new life cycle begins. How many eggs a female can lay depends on the species.