If all marijuana growers were asked what the bane of their existence was, many (if not most) would answer, “bud rot.” Bud rot can be incredibly devastating to any marijuana crop, due in large part to the fact that it comes after nearly an entire season of growing healthy plants, only to completely ruin the buds in the end.
Not only does bud rot have the ability to ruin months of hard work, it also can take hold and destroy everything in one mere week – or less. For that reason, prevention is key. Once bud rot takes hold, it can be extremely difficult (if not impossible to get rid of). Find out how to detect and fix the problem and be sure to check out my free Marijuana Grow Bible for more pro tips.
Bud rot: an introduction
If you are not already familiar with bud rot, it is important to have a basic understanding of the fungus in order to know how to prevent it. It is also known as “gray mold” and is a type of fungus or fungal disease. Like all fungi, it thrives in climates that are humid and cool.
Bud rot can occur anywhere and anytime, even when your marijuana plants do not yet have buds. The temperature and humidity level are the most important determining factors in how at risk your marijuana plants are for getting bud rot.
To get more advanced, the actual fungus that causes bud rot (or gray mold) is called Botrytis cinerea. One of the reasons it is so difficult to manage is that it rots your buds starting on the inside. Once you notice it on the outside of your marijuana plants’ buds, it is already too late to combat. The bud is lost.
Gray mold doesn’t only affect marijuana plants either. It has been known to attack strawberries, grapes (especially wine grapes), and peonies in particular. It is tough to know when your plants have been exposed to gray mold because it is spread from place to place through its dusty spores that either travel through water or blow in the wind.
Your marijuana plants won’t get bud rot unless they are physically exposed to the fungus. That may make it seem like it’s easy to prevent, but unfortunately, it’s nearly impossible to ensure that the spores never come in contact with your plants. There are certain precautions you can take to lower the chances, however.
Another aspect that needs to be in place for bud rot to take hold is some sort of physical tear in your marijuana plant’s tissue. These tears can come from training your plant (as they can be extremely small for bud rot to get inside), or they can come from insect damage. Insects such as caterpillars, snails, or worms can damage your plants enough to let bud rot inside. Even mildew can have this effect.
Detecting Bud Rot
Noticing bud rot in your plants is surprisingly easy. The tricky part comes when you want to detect it before it damages your marijuana plants’ buds beyond saving. That said, certain symptoms can lead you to take notice of bud rot before it gets too grim.
Bud rot typically starts at the youngest stems in your marijuana plants, specifically where the plant meets the soil. It softens these stems and turns them brown in color, eventually causing them to weaken and fall (known as “damping off”). Although it generally starts with the younger stems, it will certainly attack your plant’s more mature stems as well.
The beginnings of bud rot look grayish brown in color and then start to get covered in fungal spores. At this point, your marijuana plant will begin to turn yellow since it isn’t getting enough chlorophyll to stay green. Any growth above where the bud rot has taken hold all the way around the stem is going to begin to wilt.
Buds are the next target for bud rot. The buds on your female marijuana plants are especially appealing because of how moist they are. The leaves will begin to wilt and brown, and the pistils will do the same afterward. If left to its own devices, bud rot will entirely cover the buds of your marijuana plants, making them look brown, gray, and slimy. In other words, the buds are completely pointless at this point.
Sometimes bud rot can be rather tricky. It might only appear on some of the buds of your plants, or it might be more obvious in other parts of the plant first. The cola of the plant could even look like its drying up rather than suffering from what you might expect bud rot to look like. But do not be deceived.
Even the outsides of the buds could look like they are drying out, even though bud rot specifically targets the wettest part of any plant. Be especially wary of the area near the colas of your plants if they have particularly large colas, as those areas are not exposed to much air circulation and are generally attacked there by bud rot first.
Bud rot can be dealt with if you notice it when it still looks white and fluffy rather than gray, brown, dark, and dusty. It is uncommon to catch the mold in this state, however, meaning that as soon as you notice any bud rot on your buds, it’s likely too late to save those buds. Check inside the buds just to be sure – if they look dusty, brown, or dark gray on the inside, then your bud has been lost.
Bud rot occurs most commonly in environments without much light. Therefore, having lots of light to begin with is one way to combat the potential development of bud rot.
Our Symptom Checker can help you identify any problems.
Fixing the Problem of Bud Rot
Although bud rot can be absolutely devastating, the good news is that there are specific things you can do to prevent it from ever taking hold on your precious marijuana plants to begin with. This means not only keeping the environment a toasty warm, dry place with good ventilation but also taking other types of precautions to prevent any unnecessary risk of gray mold exposure.
As a general rule of thumb, the temperature of your grow room should always stay above 70 degrees Fahrenheit. Even though there should be enough humidity for your plants to stay healthy, that should remain below 50%. This is crucial when trying to avoid the development of bud rot.
Of course, outdoor growers don’t have it as easy. There is no sure way of preventing their plants from being exposed to gray mold blowing in the wind or making it to their plants through the water. Therefore, be glad that you are an indoor grower who can perfectly control your growing environment.
Another way of preventing the development of bud rot is not to let your plants get too bushy and dense in terms of leaf growth. You can train or prune your plants to maintain the proper shape without too high of a density, thus allowing plenty of ventilation to permeate the foliage of your plants. Plants with densely growing leaves are more likely to develop bud rot because there is a greater opportunity for moisture to get trapped.
Pruning your marijuana plants should be done carefully. Make sure you don’t remove a high number of leaves all at once, as this will not only shock the plant but will also cause your plant to lose many valuable sources of energy. Remember that marijuana plants get their energy from their leaves being exposed to direct sunlight.
The best way to remove any leaves is to take away the ones that are already receiving little or no direct sunlight, or ones that are blocking numerous other leaves from getting lots of direct sunlight. This will be the most efficient way to lower the density of your marijuana plants’ leaves.
Other preventative measures that should be taken include changing your clothes before going into the grow room, as clothes can easily serve as transport for bud rot spores. This will have the added benefit of being preventative for a number of other pests being exposed to your plants. If you happen to have a cat or dog, be sure it always stays away from your grow room.
Any types of tools that you use on your marijuana plants should be sanitized before and after use. The same applies to outdoor grow setups as much as possible. For outdoor plants, watering is also an important thing to think about. Or, rather the timing of your watering schedule. The best time to water marijuana plants which may be at any risk for developing mold is during the heat of the day.
Watering your marijuana plants in the middle of the day allows them to properly dry out before the cooler, darker nighttime takes place, which is when bud rot would best start developing. Even indoor marijuana setups can follow this basic logic. Whatever type of setup you have, make sure your plants have an adequate amount of time to dry out afterward before nighttime or the lights are turned off.
Another element that should be paid attention to is ventilation. Keeping air moving across your plants does wonders for keeping them dry and healthy. Bud rot thrives in a dark, cool, still, moist environment. Taking away each of these elements one at a time is an excellent way of reducing the risk of bud rot. The key is to make sure the air is touching all parts of the plant, not just the tops.
Other, more aggressive ways of preventing bud rot from developing include using bacillus subtilis spray or a sesame oil spray or neem oil spray onto your plants so that there is another barrier preventing the gray mold from getting started growing. Potassium Bicarbonate does the same job and is also organic.
If you do discover bud rot on any of your plants, remove the entire plant right away. Losing one plant to protect the others is well worth it. Whatever you do, don’t add this plant to a compost pile, as that will spread the mold far and wide. Seal it into a plastic bag and then discard it. Some people manage to prune the affected parts of the plants successfully, and the rest of the plant continues living. This is by no means a surefire way of saving the plant, however.
Other methods include copper sulfate mixed with slaked line, used commonly by vineyard workers to prevent bud rot. Copper soap and copper spray are also available for use throughout your plants’ lives. Then spray your plants with sulfur, so the treatment takes to the air and spreads.
Outdoors plants are at the greatest risk for developing bud rot after rain. If there is rain in the forecast and you know well enough in advance, try putting a tarp over the plants to prevent most of the water from getting in. Be sure that there are no spots for water to pool on the tarp. If the rain happened before you could do anything, get back to your plants as soon as possible and physically shake each one of them.
A Few More Tips
Marijuana plants with bud rot will start to have a burnt, browning look around the edges of their leaves. These leaves will eventually turn dark and purple altogether and perhaps will grow spots as well. The leaves could simply grow abnormally as well -- so if you see any strangeness developing on your marijuana plants’ leaves, be sure to take a closer look.
Whatever you do, don’t use fungicides when your plants are in their flowering phase. This could have a detrimental effect on the taste and smell of your buds. If you do discover gray mold in your indoor grow setup, there is probably something about the environment that you can change to make it less hospitable to this pest.
Keep in mind as well that you may need to harvest your plants early if you start seeing widespread signs of bud rot. Better to harvest your plants early than not at all, of course! Harvesting early does come with a greater risk of mold developing during the drying process, so remember that the risk does not go away once you've harvested.
Find more on bud rot on my blog and be sure to prevent it.