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In this guide you will learn

Fungi and diseases are very annoying and they can cause major damage to your marijuana plants. Most diseases are very treatable, but there are some you can’t stop. Bud rot starts inside the bud, which is therefore invisible until it’s in an advanced stage. Root rot is generally also difficult to spot quickly, because most roots are in soil or rockwool. That’s why it’s good to have some basic knowledge about the most common fungi. In this way, you can identify possible problems in an early stage and act preventively.

Bud rot

Bud rot is a grey mold that can be found in the middle of marijuana buds if moisture accumulates in these spots. If you don’t notice bud rot quickly enough, it can turn your harvest into a brown, unsmokable gunk in a very short time. Bud rot spreads very quickly and can ruin your entire harvest within days, so make sure you regularly check your buds towards the end of the harvest.

Bud rot occurs both indoors and outdoors, always near the end of the harvest. Make sure you properly check the leaves growing out of the buds during the last weeks. If these turn brown or grey, you might be dealing with bud rot. Gently pull on these leaves to see if they’re affected. Leaves of a healthy bud won’t come off that easily, but you can remove an affected leaf from the bud without any force. If that’s the case, bend the bud to open it and see what’s going on inside, since bud rot always starts inside the bud, which is therefore hard to identify from the outside.

If you’re growing outdoors it’s harder to prevent bud rot than when growing indoors, because you can’t control the temperature and humidity. Try to keep your plants as dry as possible by putting them under a roof. You can shake the excess rainwater off your buds after heavy downfall. Giving the plant a spot in the wind to promote rapid evaporation also lowers the chances of bud rot. It’s a great idea to put the plants inside at night if possible to avoid low temperatures and moisture.

Indoors, the chance of developing bud rot is much higher when the room is moist. Make sure you have enough extraction and aim a fan to gently blow between the buds and leaves. You can leave some more space between plants to increase air circulation. You could even cut off some of the leaves in the shadow for this purpose.

Once your plants are affected by bud rot, there’s nothing you can do besides cutting off the affected buds. I know how hard it is to have to cut off your buds at the end of your harvest, but they will infect the other buds if you don’t. Cut off the bud under the rot and bend it open to see if there’s more rot underneath. Disinfect your scissors after every cut to prevent contamination of other parts of your plant. Make sure you cut it all off. Use gloves or wash your hands well after touching contaminated buds. It’s very infectious, so it’s easy to infect your other plants.

Now treat your plants with vinegar on the spots the buds are cut off. The vinegar is acidic enough to kill all fungi, but it’s not harmful to the rest of your plants. It’s best to apply the vinegar with a brush. Throw out all buds with rot, because these are unsmokable and could even be harmful to you.

Powdery mildew

At first sight, mildew looks a lot like resin. A white layer of resin seems to be forming on the leaf, but you’ll see that it spreads very quickly. Mildew can be recognized by the pale yellow spots on the leaf, after which powdery mildew stains form. Powdery mildew creates mold spots on the leaf and downy mildew forms it under the leaf. They’re both equally harmful.

It can quickly spread if it’s been wet weather for some time or after heavy rains. The leaves eventually turn brown and wither, the buds shrivel or get infections. Plants in good condition are less sensitive to this fungus.

You can prevent mildew by having proper ventilation and the right temperature and humidity. If you still end up with mildew, you have to treat your plants. You could do this with a product like mold control, but you could also make your own, by creating a solution of 9 parts water and one part milk. This works really well. Spray on top and underneath the leaf and be careful with plants that are nearing the end of the flowering phase. You don’t want to create bud rot by wetting the buds too much.

Tobacco mosaic virus

This disease was first discovered on tobacco plants, hence the name. You can find yellow-green spots, circular figures and meandering lines on the youngest leaves. The older leaves show a yellow mosaic and disfigured leaves and they’ll quickly turn yellow. This sometimes occurs without any signs of symptoms of the virus. You often see that only one or two fingers of each leaf are infected.

An infection by the mosaic virus usually occurs in the summer and fall when there are many winged aphids. Aphids very easily transmit the virus. Once the virus is inside a plant, it’s impossible to get rid of it. Clones of this plant will therefore also carry the virus with them.

The effects on the plant are very diverse. The plant will never be able to reach its full potential, since less photosynthesis can take place because of the state of the leaves. An advantage is that it’s not as harmful as root rot or bud rot. Your plant will yield a bit less, but will still finish its flowering stage. You’ll definitely encounter this phenomenon in the future, because it’s a very common problem. Luckily it’s easy to recognize.

There are many more viruses and diseases that can affect your plants. Check the symptom checker for a complete overview. And if you’re not sure about something, feel free to post the question on the forum. There are plenty of experienced growers who are happy to help.

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