How to manage Botrytis in Cannabis

Of all of the many pests, critters, pathogens, and problems that you may encounter in your cannabis garden, one thing will always dominate the list: Botrytis, aka “bud rot”. Here we learn how to identify and manage Botrytis in Cannabis.

Botrytis is a pathogen that is introduced to your plants in the form of microscope spores. It’s an extremely common mold found nearly everywhere on the planet. As an outdoor OR indoor cultivator, there isn’t much you can do to avoid the risk of spore contamination. However, there are multiple steps that can be taken in order to mitigate Botrytis outbreaks and get the most out of your harvest.

The mechanisms that enable botrytis: There are a few major factors that inevitably contribute to botrytis outbreaks. Moisture, temperature, lack of airflow, dead plant material, flower ripeness, flower structure and genetic predisposition.

Environment

In an outdoor environment, you are largely at the whims of the weather. As they say “nature bats last”. This can’t be farther from the truth. If you live in a rainy climate, you likely have an uphill battle fighting botrytis. There are still measures that can be taken to minimize or mitigate the risks. For indoor gardens, heat and dehumidification are a must. Always minimize sudden temperature fluctuations in order to keep your dew point in equilibrium and minimize condensation. In tropical climates, it may be necessary to build a transparent roof structure over your plants. This is not an advocacy for greenhouses, in fact greenhouses are not the answer you would expect in humid environments. Greenhouses trap moisture and unless they are very well engineered, condensation will rain down on your plants and only worsen the botrytis issue.

Treat your plants delicately. Mold spores are everywhere, they are on a seek and destroy mission to find a host. Be extremely careful when pruning and defoliating. Always use sharp, clean scissors and take caution when tearing leaves from plants. A small tear may seem harmless when the plant is in juvenile stages but when it starts to ripen, the dead plant material will become an inviting host for botrytis spores.

Location Location Location

Outdoor gardens locations should be carefully chosen. Sites with poor southern exposure and lack of morning sun are the most vulnerable. Southern facing walls are a a great backdrop, the thermal energy stored in the wall will help radiate the the plants with enough warmth to keep them above the dew point during crucial morning and evening hours. Areas with good airflow will inevitably fare better than stagnant areas with little to no airflow. Examine the wild fauna around your proposed locations and avoid areas where you already see Powdery mildew, rotting detritus or fungi.

Genetics: plant structure, early ripening, flower density and overall resistance.

Genetics absolutely play a role in resistance of mold and mildew. However, genetics aren’t the key ingredient. It’s important to understand that all cannabis flowers will mold with the right mechanisms. Early ripening varieties are the best bet against nature. As fall approaches temperature fluctuations become more pronounced and these fluctuations in-turn lead to dew-point fluctuations. Plants with really big colas and thick canopies are almost always more likely to mold than plants with thin leaves and spaced out flowers. Big, dense colas trap moisture and inhibit airflow. Lastly, some cultivars have a cellular structure that is more resistant to botrytis than other cultivars.

Proper Pruning and Maintenance

Keep your plants healthy, healthy plants with strong cell walls will naturally defend against the intrusion of botrytis spores. Proper pruning is an absolute must, this is true for both indoor and outdoor cultivation. The key word being “airflow”. Plants with thick sets of leaves should be pruned in order to allow airflow through the plant. Prune the bottom branches liberally in order to create an inverse pressure gradient that forces air upwards through the plant much like an airplane wing gets uplift. Proper pruning will have a profound impact on the mold resistance in your garden.

Early Identification and Removal

Once you spot botrytis in your garden, you already have a major problem. Early identification can make the difference between a partial loss and a total failure. The earliest signs of botrytis usually show up as a single wilted or brown leaf coming out of an otherwise healthy looking bud. Botrytis usually affects the largest, densest and most ripe buds first but this isn’t always the case. If you spot mold, it’s imperative to complete a full damage control assessment. The rot will spread incredibly fast so do not hesitate to remove and destroy all infected areas. If the damage is centralized to small specs, do your best to remove any and all infected areas, if the damage is widespread, you will likely need to remove entire buds. Oftentimes, “spot harvesting” the plant can greatly mitigate the issue. Try harvesting all of the big vulnerable tops and leaving the bottoms to ripen up for a while longer.

Dry it Fast and Warm

Unfortunately, if your crop is molding upon harvest, you will need to throw your typical drying and curing etiquette out the window. Botrytis will spread like wild fire, even after harvest. I have personally witnessed harvested crops go from 25% loss to 90% loss during the drying process alone. This was user error and could have been prevented with an aggressive drying regimen. For best results, dry your flower at 80-85f and 35-50% humidity. The warm dry air will quickly inhibit the mold from growing