Growing Marijuana and Bud Rot?

When growing Marijuana, the aim of the game is to produce the biggest and best buds possible. Whether it has personal or commercial value, as a grower we wish to harvest the buds in a straightforward process. However, there are many potential factors that can seriously threaten a final crop and even wipe out a complete garden in less than a week.

One serious threat is a necrotrophic fungus that growers call Grey Mould or Bud Rot. The scientific name for this spore is Botrytis and it is a real problem if you don’t understand it. If left untreated and in the same environment, Botrytis can wipe out an entire budded crop within a week, rendering anything it attacks useless and unsmokable.

Bud rot can appear within the final stages of the flowering period, there are many variables that can cause the perfect environmental conditions for these spores to thrive within a grow room. It is not very difficult to diagnose mould or bud rot in your plant, especially if you have seen it before. Mould and bud rot affect plants in a similar fashion and can be prevented and treated using the same techniques. Bud rot usually goes hand in hand with discoloring of leaves and buds and a much weaker structure. If you are not sure whether a bud is infected, another easy way to check for bud rot is by gently pulling at the leaves that stick out of your buds. If these leaves come out very easily or are discolored on the portion that was inside the bud, it is very likely that the bud is infected.

How Does Mould Or Bud Rot Get Into My Grow Room?

Spores which travel in the air are responsible for this fungus to enter the garden. When growing Marijuana, we are always under threat from outside sources which carry potential airborne fungal spores, pathogens and even male pollen into the grow room. There is a great deal you can do to prevent these spores from entering your grow room but once they do, they will remain present as long as the atmosphere is suited for their survival. Wind and rain are responsible for carrying these spores, so the actual source of the problem is always out of your reach when growing Marijuana outdoors.

Conditions For Mould To Thrive?

Creating the perfect conditions for the plant during the growing and flowering phases is vital. When growing Marijuana, the humidity should be high during the growing phase, while during the flowering stage humidity should remain below half of what it was in the growing phase. Botrytis thrives in very wet conditions with very humid air, poor air circulation and a damp soggy growing medium. All of this means that there is a serious problem with the growing environment if the air circulation is not adequate and the temperatures and humidity are not correct.

Preventing Mould When Growing Marijuana Outdoors

For indoor grows these variables can be checked and adjusted individually, however when growing outdoors it is not possible to control all of these conditions. Weather conditions towards the end of the outdoor season are usually favourable for mould and bud rot, as this is when temperatures drop and humidity rises. A good thing to keep in mind when growing Marijuana outdoors in zones with suboptimal climates during the normal flowering season is that there are several ways to harvest your plants before this normal flowering season. The most straightforward way to prepare for bad weather is to grow a strain that is mould resistant and finishes flowering relatively early like Gold Rush Outdoor. Another great option is growing autoflowering strains that finish their flowering period within a set time frame like Dutch Automatic, Dutch Blue Automatic, AK Automatic or White Widow Automatic. Photoperiod strains can also be manipulated into flowering early through light deprivation, a technique that is further discussed in our blog.

Aside from growing a different strain or flowering your plants early, there are several measures you can take to help prevent mould and bud rot. If you are growing in a greenhouse, adding a small heater and keeping the air fresh can allow the conditions to remain spore free. It is not really an option to add a heater or fans to a true outdoor grow, but protecting your plants from moisture and improving airflow can already go a long way. Rain and even dew cause a lot of trouble towards the end of the season because wet buds will not dry as fast as during the hot summer months. Simple measures like shaking the water off of your plants in the morning or after rain can be very meaningful in preventing bud rot or mould. Better yet, you can put your plants under a roof to shelter them from the rain or even keep them inside at night. Ensuring there is enough space between buds and side branches can also allow for better air circulation in and around the plants. This additional space can be achieved in many different ways and usually involves pruning and training plants. It pays off to inspect your plants on a daily basis during these last few months of the season. You may not be able to completely prevent bud rot, but you will definitely be able to stop it from ruining your entire crop.

In the following video you see a grower taking care of his outdoor garden by pruning excess leaves to improve airflow and shaking the dew off of the buds. These simple techniques are a quick and effective way to prevent bud rot.

Can I Save A Growing Marijuana Crop Once Infected?

If you have identified a bud rot infection when growing Marijuana, action should be taken as soon as physically possible to prevent any further damage. This fungus is not to be ignored and can turn a crop into a slimy mess or a grey candy floss texture in days.

You can stop and prevent the spreading of Botrytis by following these steps:

Start by wearing latex gloves and clean scissors and sterilize both with alcohol. Carefully remove the mould off the buds and infected areas. The infected parts will fall away like candy floss and may even be slimy. Once you are confident you have removed any visible mould, sterilize the scissors with alcohol and throw the gloves away.
After removing the afflicted areas of your plant, you can include an optional step that involves cleaning these areas with an organic disinfectant. Commonly used products to treat Botrytis in commercial organic agriculture like Serenade by Bayer work very well for this purpose, but easier options include using a garlic concentrate, vinegar or hydrogen peroxide. Spraying areas you have removed Botrytis from with a 5% hydrogen peroxide solution will kill off the remaining spores and prevent further infection. But be careful, as too much of these disinfectants, even if they are organic, can also damage the plant!
Clean out the entire grow room with a bleach solution. This means wiping the walls, floors, ceilings, fans and pots. When every part of the entire grow room has been treated, the room should be spore free.
Keeping the grow room as clean and sterile as possible will eliminate spreading of any old Botrytis spores. The temperature and relative humidity in your grow room need to be perfect to ensure the spore cannot survive as it once did in the wet and damp environment. When growing Marijuana correctly, maintain a daytime temperature of 23°C and a nighttime temperature of 20-22°C. Keep a fan lightly blowing against the buds and with correct temperatures, air movement and a relative humidity of 35% the crop will grow mould free.
Using a dehumidifier can also aid the prevention and removal of Bud Rot. This is also a good idea if growing in a large greenhouse as these are prone to being too humid. A dehumidifier can alter the humidity levels to a comfortable 30-40%. Also consider the containers you are using, sometimes growers will use containers that are too large for their growing Marijuana plants. These can hold too much moisture within the medium, causing more issues later on.

Can Growing Marijuana Buds Mould From The Inside Out?

When growing Marijuana, mould can be identified when the outside of the flower is damaged. The symptoms of Botrytis will look like grey spider web on the surface of the buds, the fan leaves around the infection will often also be damaged. Often a grower can harvest what look like perfectly formed huge buds, only to find that once the buds are opened, the mould has grown from the inside out. These buds are completely ruined and the grower is left with 20% of the intended yield!

Mould formation from the inside out can occur when buds are so dense that airflow is restricted to parts of the buds. If this goes untreated for extended periods of time, the insides of these buds can become breeding grounds for fungus. If bud rot spreads in this fashion it becomes much more difficult to properly diagnose the problem, making it even more important to pay close attention to your plants. Yellowing of leaves, especially if this starts from the buds rather than from the leaf tips can be a sign of infection. Another way to confirm the presence of bud rot is to gently pull at the small leaves that stick out of your buds, if these leaves come out with little to no resistance it is very likely that the bud has been infected.

The denser your plant is, the more important it becomes to ensure the airflow is ideal. This means having oscillating fans blowing at the bottom and tops of the plants. When growing Marijuana, even during nighttime when the lights are out, having constant air movement prevents the growth of Botrytis and Powdery Mildew. The important thing to remember is that as long as your environment is right, this problem cannot exist.

Can You Smoke Bud Rot Infected Marijuana?

The answer to this is definitely no: you can not and should not. Infected buds that were left to harvest will be a dark golden brown and severely dried out. Smoking these buds would be a danger to your health and they should be removed. You will notice that the buds around affected areas look OK, possibly with some darkening of the final colour. Throw away any buds that have lost colour or become a dark golden yellow, as they are possibly infected with bud rot.