• Post last modified:February 2, 2022
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Cannabis cultivators are often faced with numerous challenges that sometimes result in the loss of an otherwise would have been bountiful harvest. One of these challenges is bud rot. This mold destroys plants at an alarming rate, leaving growers with steep losses and disappointments. This is especially true for beginner growers. Learning everything there is to know about bud rot puts you in a position to nip the infestation in the bud (no pun intended) before it’s too late to recover. This piece covers what bud rot is, what it looks like, the causes, and how to prevent and stop it. 

What is bud rot?

Also known as gray mold, bud rot is a mold that attacks the stem that the flowers/buds are attached to. With time, this interferes with the water and nutrient supply to the buds and leaves, leading to their death. Bud rot is caused by a parasite known as Botrytis Cinerea, and it affects both outdoor and indoor-grown cannabis plants.

Salvaging the bud rot situation might be attainable depending on the promptness of the actions taken after the parasite strikes. If detected early and the affected buds are removed, the other plants can grow normally and produce yields as expected. 

How fast does bud rot spread?

Very fast! The parasite is highly contagious and can quickly destroy your plants within a few days.

Stages where your plants may be susceptible to bud rot 

Bud rot becomes a threat from the beginning of the flowering stage until the drying and curing process. That’s right! Even after having a long, successful growth period, your buds are still at risk from Botrytis Cinerea. How fast you trim the buds after harvesting, the drying room conditions, and the curing procedures may or may not lead to bud rot infestation. 

bud rot on marijuana

What does bud rot look like?

Bud rot goes through 3 stages once it strikes. Initially, it presents as a feathery white mold. This is the first sign of the mold working itself from the core of the bud to the outside. If it goes undetected, the mold turns grey and is accompanied by yellow and brown, wilted leaves that appear burnt. The final stage is when the rot turns black. At this point, it is impossible to salvage anything as the damage is already done. The buds become slimy and have a pulpy consistency.

This image (left) is bud rot in its early to mid stages, it has already began to turn a brownish colour. Salvaging bud rot ridden plants isn’t easy, however as this particular patch was an isolated issue and caught early you can save the plant by removing the infected area.

Below is a list of signs indicating bud rot;

  • Yellow, wilted leaves that look burnt.
  • Rotting, foul odor
  • White mold on the flowers/buds
  • Black spots on the leaves
  • Inconsistent leaf growth
  • Rotten buds

What causes bud rot

Are you wondering what causes bud rot? Well, cultivating cannabis in a grow space/environment characterized by below-optimum air circulation and high moisture levels create the perfect flourishing site for mold. The chances of bud rot occurring increase if you grow closely packed, thick plants with dense buds. Their ability to retain water is higher compared to spaced-out, less dense plants. It is easier to control humidity, airflow, and temperature indoors than in a greenhouse or outdoor setup. Consequently, bud rot is more rampant in any outdoor setup. 

Identifying bud rot

Early detection of bud rot is critical in saving your cannabis plants. Unfortunately, it is impossible to diagnose the disease before it displays any signs. This is because it affects the core of the bud before destroying other parts of the buds and the leaves. Ensure you conduct regular inspections of your plants to get ahead of the situation when it matters. If you suspect your plants may be infested, examine the cracks and crevices of the buds in question. 

Take a good look at the core and if it looks pulpy and brown, remove the plant and others showing similar signs. Put that area under quarantine in case the remaining plants have been infected but are yet to show any signs. Bud rot can be transferred from one plant to another through spores by agents such as wind, water, insects, or anyone working on the growing area. To avoid this, ensure you and all grow room employees wear different clothing when handling the healthy plant section from the bud rot-ridden one. 

How to stop bud rot

Salvaging bud rot is not as easy as preventing it in the first place. However if a few plants or a section of your cannabis plants have bud rot, the mold may have spread to other areas within the same grow environment. At this point, you need to choose between harvesting everything immediately or isolating the affected plants and letting the healthy ones complete their growth cycle.

If you pick the latter option, ensure you conduct a thorough inspection of all plants. Remove any plant that shows signs of bud rot and isolate them. Always ensure you wear gloves and that all equipment used during this process, such as scissors or trimmers, is tossed or thoroughly sanitized. Lastly, avoid utilizing treatments that will affect your buds’ final quality (appearance, taste, and smell), such as fungicides or sulphur. 

how to stop bud rot

“Bud Rot is easier to prevent than cure: Use fans to improve air circulation with indoor grows and reduce the risk of bud rot ever occurring in the first place.”

How to prevent bud rot from affecting your cannabis plants

A sure way to prevent bud rot from affecting your plants is by providing optimum conditions that discourage the parasite from thriving. Below are tips on achieving this when cultivating indoors or outdoors. 

During the flowering stage

Growing Indoors

  1. If you have bushy, dense plants, try and defoliate the lower and middle leaves to facilitate optimum airflow.
  2. If there is high humidity where you live try growing a strain that is better suited to this kind of climate. Sativas such as Amnesia Haze, Thai Stick and G13 Haze all grow naturally in hot humid environments and have less dense foliage so will be much less susceptible to but rot.
  3. Invest in exhaust fans
  4. Conduct regular inspections of your plants, especially the denser ones.
  5. Maintain a humidity of about 40% to 50% throughout the flowering stage. 
  6. Keep the plants spaced out.
  7. Use humidifiers to regulate the amount of moisture in the grow room
  8. Maintain a temperature of 75 to 77 degrees Fahrenheit throughout the day. Lower the temperatures by 5 to 10 degrees during the night to allow the plants to cool down internally. 

Growing outdoors

  1. Avoid flower to flower contact by trellising your cannabis plants
  2. Get rid of unnecessary plant matter
  3. Drain stagnant water within the cultivation site
  4. Blow dew from the plants every morning. If you are cultivating cannabis during the rainy season, you can build a temporary shelter to keep the excess water away. Alternatively, you can use an electric leaf blower every time it rains. 
  5. Inspect the plants daily, especially the dense ones
  6. Space the plants sufficiently

During the drying and curing process

  • First, you should never harvest your cannabis plants if it has been raining for two or more consecutive days. Harvesting under dry and cool conditions lowers the bud’s moisture significantly. 
  • After harvesting, don’t let the plants sit around for an extended time. This creates an opportunity for the mold to strike. 
  • Do not overstuff your drying room. Space the plants such that they do not touch. 
  • Invest in fans to maintain regular, healthy airflow
  • Keep the plants in a dark room with temperatures of 60 to 70 degrees Fahrenheit. The humidity levels should be at 50% within the first three days then increase to 60%.
  • Trim your buds entirely before starting on the curing phase. 
  • Ensure that the buds do not feel moist when touched before initiating the curing phase. The stems should snap and not bend, indicating proper drying.
  • Once you put the buds in an airtight container, ensure you burp them several times a day for the first two weeks. This allows the moisture trapped inside to get out and lets in fresh air. 

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