Bud rot is a type of mold caused by the fungus, botrytis cinerea. The term “bud rot” describes how the fungus attacks cannabis plants – it rots the buds from the inside out. This fungal disease is also known as “gray mold” due to its dark gray color, but the mold can be brown, too.
Bud rot can attack cannabis plants in all stages of growth. It can strike in veg, in flowering… you can even suffer bud rot after harvest, but how do you know if you have bud rot? How does bud rot occur? How do you prevent bud rot? And, more importantly, can moldy buds be saved?
What causes bud rot?
Exposure to dusty grey mold spores is what kicks off a fungal infection, and it can be difficult to avoid them! Botrytis cinerea can be transported in air and water, on animals, clones, even clothing.
Gray mold can invade a plant through wounds or tears from pruning or training. Insects such as worms, caterpillars and snails can also create access wounds. Mold will thrive in the humid conditions that cannabis plants enjoy, but there are preventative steps every good gardener should be taking. If you suspect your plant is already suffering from grey mold, here’s a few things to double-check.
What are the early signs of bud rot?
Bud rot starts as a fluffy white mold that spreads throughout the interior of the plant. It often targets the youngest stems first, although it will attack other stems as well. Spotting the infection at this stage allows growers to mitigate the problem. You should check online for bud rot pictures to double-check you’ve made the correct diagnosis.
What are the later stages of bud rot?
Bud rot forms a grayish or brownish mycelium mass that softens the affected stem. The insides start to turn brown or gray as the mold grows, filling the insides with dusty-looking spores. The plant will lose its green color and turn yellow due to lack of chlorophyll. It will start to weaken and fall over, causing any growth above the affected stem to wilt. This stage of decay is called “damping off”.
If you have spotted these bud rot signs, the spread is already severe, though the bud rot will continue attacking the plant. After the stem, it moves on to the buds.
The advanced stages of bud rot
After it begins infecting the buds, the leaves will start to brown and wilt. The pistils will follow shortly. The bud rot will eventually cover every bud with slimy, grey-brown mold. At this point, the plant is a dead loss.
These symptoms of bud rot do not look the same in all affected areas. Some plants have it worse in the buds, while the others show more infection in the stem. Once it’s inside the stems, it might be too late to save the buds.
How do I prevent bud rot?
With cannabis, the old adage “prevention is better than cure” is true. Spores can attack a cannabis plant at any time through many means, but there are preventative steps you could and should be taking.
Can you suggest a mold-resistant cannabis strain?
Some strains are naturally more resilient to mold and bud rot, while others are more vulnerable. Your defense against gray mold spores starts with choosing the right cannabis cultivar. Growers with limited experience should definitely be choosing the right cannabis strain. These are our top picks of mold-resistant marijuana strains:
A native of South Africa, Durban Poison is a landrace resistant to both mold and disease. For a sativa strain, it flowers quickly at only 8 to 9 weeks. It’s suitable for growers of all experience levels.
A great choice for growers who prefer an indica plant, Northern Lights is a joy to grow. It only spends 7 to 8 weeks flowering and shows resilient growth from sprout to harvest.
Sweet but potent and hardy, Strawberry Cough can handle harsh, wet conditions, thriving even in poor environments.
Growers who can’t decide between indica or sativa should think about cultivating White Widow. It’s a balanced hybrid that can resist invasive fungi. Because it’s such a resin-heavy strain, it also shows good pest-resistance as it flowers.
Optimize your cannabis growing environment
Preventing bud rot in an indoor grow
The great thing about growing cannabis indoors is that cultivators have control over almost everything.
What’s the ideal humidity level to prevent cannabis bud rot?
In an indoor setting, a simple dehumidifier will let you keep humidity levels low, (ideally, between 40% to 70% during vegetation). When the plants enter the early to mid-flowering stages, the optimum humidity must drop to 40% to 50%. In the later stages, it should further dip to below 40%. Use a hygrometer to measure levels inside the grow room or tent.
What’s the ideal temperature to prevent cannabis bud rot?
During the vegetative phase, the most ideal temperature in a grow room or grow tent is around 22–28°C (71–82°F) during the day and 18–24°C (64–75°F) at night. Then, as the plant flowers, you should lower to 20–26°C (68–78°F) during the day. As you reach late flowering stage, drop the humidity levels to 30–40% while keeping your temp between 18–24°C (64–75°F) during the day, with a cooler 16-20°C (61-68) during the very last few nights.
Preventing bud rot in an outdoor grow
Growers have far less control over the environment when growing cannabis outdoors, but there are certain things you can do.
What’s the ideal location for growing cannabis outdoors?
Selecting an optimum spot for a cannabis can help minimize the risk of bud rot. A grower must visit the intended site several times before planting, making sure it always has plenty of sun and at least a gentle breeze (though hurricanes, tornados and strong gales should be avoided).
What is the best climate for growing cannabis outdoors?
Your climate should definitely inform your cannabis strain selection. Indica plants can manage better in cooler climates, while sativa plants thrive in warmer regions. Auto-flowering varieties can do well pretty much anywhere besides deserts and frozen tundra.
What do I do if adverse weather sets in?
After rainfalls and drops in temperature, cannabis plants are at a higher risk of gray mold. You need to be able to both monitor and react to these types of weather changes.
Building a portable, removable shelter for your plants will give you an effective (if rudimentary) way to keep off the rain. Make sure the cover does not come in direct contact with the plants, with ample overhead space. It should also be constructed with a ‘fall’ so the rain doesn’t puddle in the middle.
After a shower of rain or during mornings with heavy dew, shaking the plants to get rid of water droplets also helps.
Pruning and training your cannabis plants.
Having proper air circulation is critical in preventing the growth and spread of gray mold. The foliage should be able to breathe. Air moving freely throughout the plant will help keep it healthy and dry.
Pruning and defoliating is a good way to facilitate airflow, reducing the chance of moisture accumulation on the inner and lower parts of the plant. Remember to remove a few leaves at a time, though – you don’t want to overly shock the plant. A plant gets its energy from the leaves so be careful not to remove too many!
Training is also a good preventive measure, especially if the density of the leaves is not that high. By separating the colas, growers can increase the ventilation.
Feeding and watering your cannabis plants.
Bud rot loves moisture and darkness. When combined, the chances of Botrytis mold growing on the plants increases dramatically. Following Kyle Kushman’s Feeding and Watering guide will help you keep excess moisture to a minimum, lowering the odds of bud rot. Correct watering gives the plants an opportunity to dry off before the sun goes down and when it is time to turn off the lights. This can prevent humidity at night time.
Grow cannabis organically or veganically.
Plants should be reasonably healthy in order to fend off mold more effectively. To improve the immune system of the growing plants, you can feed the soil with organic compost or veganic nutrients. Using compost tea can increase the beneficial microbes in the soil, helping to keep the plants strong and healthy.
Observe your cannabis plants.
In addition to the usual routine of watering the plants, adding fertilizers, turning the lights on and of and so on, keeping a close eye on the plants can help detect bud rot before it becomes full-blown. Cannabis plants are more vulnerable in the later stages of the flowering phase, but you should monitor regularly throughout all stages of growth.
Cleanliness is next to godliness.
Because gray spores cling to all surfaces, including clothing, you really should change clothes before stepping into the grow room. This will cut the risk of unknowingly introducing spores and other pathogens. Keep your pets away from your plants and keep everything clean – especially pruning shears and the surfaces inside your tent.
Bud rot is still a risk during and after harvest
The risk of bud rot is a little lower during and after harvest, though there is still a very real danger – harvested buds are not immune! Make sure you follow these steps to minimize the post-harvest risks.
Harvest your outdoor cannabis plants during a dry spell.
Your outdoor cannabis will have lower moisture content when it’s not rained for a few days. You will be taking dryer buds into the hanging room so the plants will dry at a more optimum rate.
Inspect your cannabis plants before, during and after harvest.
Removing any affected parts of a plant is essential BEFORE the plants go into the drying room. Be vigilant.
Trim the buds before hanging.
Trimming the buds and removing the fan leaves decreases the amount of moisture in drying room. It also improves airflow around the buds.
Hang The Plants Properly
When hanging, the colas and branches should have ample space in-between to allow proper air circulation. Normally, they can lightly touch each because they will contract over time, but if there is any evidence of bud rot, you should keep them apart – even if you think you have removed all affected areas.
Drying cannabis plants in the correct environment.
Make sure your drying room has:
- about 50% humidity level
- a temperature of around 70°F or 20°C
- air circulation
A fan is a good friend in the drying room, but never aim it directly at the plant – airlflow needs to be as passive as possible.
Adjust The Drying Speed
If mold is an issue, it might be better to quicken the drying process. Increasing air circulation, decreasing humidity and increasing the temperature can help cannabis plants dry faster. Note, though, that this will have an impact on the buds’ overall quality.
How do I get rid of bud rot?
When bud rot hits, there aren’t many things a cannabis grower can do. With limited options on the table, let’s take a look at what you can try to get rid of bud rot.
Destroy the affected cannabis plant.
Once the bud rot becomes too widespread, cannabis growers usually have no other option but to throw away the whole plant. ALL rotted plants MUST be removed to stop the disease from spreading to healthy plants.
While removing the infected plants, do not let them touch the unaffected plants. Once removed, each one must be put away in a sealable plastic bag. It cannot be added to the compost pile since this would only spread the contamination.
Remove the affected buds and leaves.
Although throwing away the whole plant is advisable, some growers try to remove the affected parts in the hope the unaffected areas will survive.
The proper way to trim the plants is to cut 2 to 4 inches below the bud. If there are many infected buds, growers should sterilize the cutting tool after each cutting.
The bagged infected parts should then be destroyed immediately.
How do I stop bud rot coming back?
Once your cannabis plants are free from bud rot, growers can help the remaining ones stay healthy by improving the environment. Following the precautionary steps provided above can decrease the chances of bud rot coming back.
If you can’t improve the current grow space, you could move them to a better site entirely. The new site must be warmer and dryer with adequate air circulation.
Preventing bud rot is key.
Bud rot and other types of mold are part and parcel of a cannabis grower’s life. The best thing to do is take every precautionary measure to prevent gray mold, and don’t be afraid to cut your losses if you have a bad contamination. It’s heartbreaking having to throw away your cannabis plants but sometimes, the best lessons are the ones that hurt the most.
Can I use sprays and fungicides on my cannabis plants?
A more aggressive approach to preventing bud rot is spraying Bacillus subtilis, a non-chemical probiotic bacteria. Also known as hay bacillus or grass bacillus, it can be useful in fighting bud rot and some strains of mildew. It naturally occurs in the soil and is considered by many to be a responsible, organic solution to cannabis bud rot.
An oil spray containing Sesame oil or Neem oil can form a barrier on the plants that will prevent the Botrytis mold from thriving. Due to its low toxicity, it does not present risks to animals, humans and beneficial insects. It will adversely affect the flavor of your buds so make sure you only use it during veg.
Potassium Bicarbonate (KHCO3) is a widely-used natural compound that usually comes in powder or crystal form. When mixed with oil, castile soap and water, it becomes a powerful solution against powdery mildew and fungal diseases.
What about fungicides?
Fungicides should not be used during the flowering stage of the cannabis plant. This goes for chemical sprays, burn sulfur and Neem oil.
Since bud rot cannot be treated with any fungicide after it has spread, spraying should only be done as a preventative measure. It should be used before the plant has started producing buds.