If you are a farmer, it doesn’t matter whether you are growing cannabis or tomatoes; every crop has its challenges. Just like any other plant, cannabis is susceptible to all kinds of problems, including fungus, pests, infestations, and diseases. If you are noticing wilting and yellow discoloration of your cannabis crop, you might be dealing with verticillium wilt. Verticillium wilt on marijuana plants can be a massive headache for a grower – especially if you don’t catch it early.
The key to treating verticillium wilt on marijuana plants is correctly identifying the disease (which can be tricky as the symptoms mimic many other marijuana plant diseases) and preventing it by using healthy compost, proper soil drainage, and selecting plants with strong genetics.
What is Verticillium Wilt?
Verticillium wilt is a fungal disease that attacks the roots of a plant and travels up the plant’s vascular system through the xylem. Here’s a little biology lesson for you: The xylem is the part of the plant that transports water from the ground, trough the roots, up the stalk, and into the leaves. When verticillium fungi get into the xylem, it blocks the vessels that allow water to enter the plant and produces toxins that spread through the plant instead. This is what causes the plant to die off, yellow, and wilt.
Verticillium wilt doesn’t just occur in marijuana plants – it can happen in all kinds of plants like cotton, tomatoes, potatoes, peppers, eggplants, melons, peppermint, strawberries, pumpkins, hops, alfalfa, sunflowers, and more. Many large-scale commercial agriculture professionals fumigate their soil before planting these crops just to prevent verticillium wilt. The fumigation is made with very expensive chemicals that kill off the fungus in the soil, but are toxic to your health and the environment ? which is one of the reasons why it is important to purchase the organic variety of certain fruits, vegetables, and herbs.
Verticillium wilt fungi can live in soil for several years. It is most common for the fungus to develop in soil that has poor drainage and is rich in nutrients. Usually, verticillium wilt thrives in areas that are humid and maintain a temperature of 68-82 degrees Fahrenheit. For that reason, the disease is common in areas like the Pacific Northwest in the United States. It can occur in other parts of the world as well, but is more prevalent in spring and fall when those warm, humid conditions might exist.
How Do You Diagnose Verticillium Wilt on Marijuana Plants?
The symptoms of verticillium wilt show up in two places on marijuana plants, the leaves and the body of the plant. In a plant with verticillium wilt, you might notice:
- Yellowing, drooping, and dying leaves, especially at the base of the plant
- Sudden and severe wilting that gets worse in the hotter parts of the day
- Browning at the base of the stem
- Grey-brown discoloration of the plant
- Branches die off – it’s common for verticillium wilt to affect isolated parts of a plant
How To Treat Verticillium Wilt on Marijuana Plants
One of the problems with verticillium wilt is that the symptoms are almost impossible to spot until it’s too late. Once the fungus enters the plant, there is nothing you can do about it other than destroy your plant and treat the soil. As soon as you spot the signs of verticillium wilt in a young marijuana plant, rip it out of the ground, dispose of it, and leave the soil alone. You definitely do not want to put another plant in its place because that one will surely get the fungus as well.
The key to getting rid of verticillium wilt is taking preventative measures with your soil and using best practices for growing plants in soil. Here are some ways you can prevent verticillium wilt:
- Grow your plants in high-quality soil
Verticillium wilt can live in soil for years – so you want to make sure you are planting your cannabis in potting soil that is free from disease. Be sure to purchase sterilized compost and avoid working with soil you know is infected with the verticillium fungus. If the fungus hit your crop, dispose of the plants and do not put them into your own compost. This will only cause the disease to spread again the next time you plant. You may also want to plant your cannabis in containers instead of straight into the ground if you are working with land you have never farmed before. This eliminates the unknown factors that might by living in your soil.
- Make sure the plants have proper drainage
Avoid over-watering your plants and mix plenty of organic matter into your soil to ensure proper drainage. Verticillium fungus thrives in warm, wet environments so soil with excess moisture should be a red flag.
University of California, Davis has an excellent method posted online for testing your soil drainage – and it might be worth testing your soil before you plant in it. When scoping out areas to grow cannabis, remember that the water needs to drain downhill. If your growing area is completely flat, consider building a French drain. A French drain is a small trench with a 1-3 percent downhill grade that is filled with rocks. If water is pooling in your garden, this will help it flow downhill.
- Utilize crop rotation, deep plowing, and solarize the soil
If you are committed to planting your marijuana crop outside straight into the ground, there are some farming best practices you can use to lower the chances of a verticillium wilt outbreak. First of all, till your soil really deeply and blend it with a fungus-free sterilized compost. You might also consider solarizing the soil just in case. You can do this by tilling the soil, mixing in compost, wetting it, and then covering it with a clear plastic tarp for three weeks. Make sure you do this in a season where the ground will be exposed to bright sunlight and hot temperatures. The heat will kill the fungus in the soil.
Additionally, you can use crop rotation to help prevent any diseases from entering your plants. If your land was plagued by verticillium wilt, plant a cover crop that is known for being resistant to fungus. When the time comes to plant again, you can till the cover crop into the soil. Some options for verticillium resistant cover crops are sudangrass, mustard, and broccoli.
- Select plants with strong genetics
It almost goes without saying, but this is one of the reasons why you need to buy marijuana seeds and plants with strong genetics. Verticillium wilt, and other diseases as well, only impact plants that have a weak root system to begin with. It’s just another reason why you want to select your marijuana seeds from a reputable buyer ? especially if you are trying to make money from your cannabis grow.
- Ditch soil and grow hydroponic
If you live in an area like the Pacific Northwest and you are worried about diseases like verticillium wilt, you can always try out growing methods that eliminate soil-born fungi. There are many challenges to working with soil when growing cannabis, including delicate pH, susceptibility to diseases and pests, and difficulty measuring and providing nutrients to your plants. If you aren’t committed to providing your plants with healthy soil and you’re not interested in soil science, you might consider a hydroponic growing system. Of course, growing hydroponic comes with its own challenges, but you will not have to worry about verticillium wilt wiping out your crop and destroying your soil for years.