Prevent Cannabis Bud Rot: Cultivation Facility Design and Retrofit Solutions to Help Solve Your Bud Rot Problem

Bud rot in cannabis can be heartbreaking. Picture the scene: An otherwise good (maybe even great) looking crop is on track for a big yield of high-quality flower. But a short time on the harvest table quickly reveals the devastating loss that is about to take place—bud rot! 

Its scientific name is botrytis cinerea and it’s commonly referred to as gray mold. But whatever you call it, it can cause devastating crop losses. Bud rot is especially insidious because it tends to show up when everything else is going well - when buds are big, spirits are high and after the grower has already turned in their optimistic projections for the crop’s yield. Those estimations quickly get reduced by 25% to 50% (or more) once bud rot damages are taken into account. 

This blog will delve into causes for cannabis bud rot, along with other similar mold issues in cannabis cultivation, and explore solutions for both new facilities and retrofits to prevent and combat this common problem.

Understanding Cannabis Bud Rot and Related Mold Issues

Botrytis cinerea is a fungal pathogen that thrives in high-humidity conditions where airflow is poor. It primarily affects the buds and flowers of cannabis plants, causing them to rot, turn brown and become unsuitable for consumption. 

The first signs of bud rot are usually within the interior of the bud, making it easy to miss until it’s too late. Keep an eye out for single dead or yellowing sugar leaves protruding from the cola. Then trace those leaves back and gently open the bud to check for the actual mold. Bud rot can be gray or black and will often appear fuzzy. Other common mold issues in cannabis cultivation include powdery mildew and downy mildew, both of which also thrive in high-humidity environments. These molds can significantly reduce the quality and yield of the crop. 

Many cultivation facilities were not originally designed to efficiently move air or remove enough humidity from the environment, forcing operators to invest in costly and often suboptimal strategies for avoiding bud rot in their cannabis crops.

Preventing Bud Rot at New Cannabis Cultivation Facilities

When designing a new cannabis cultivation facility, it is important to consider airflow and dehumidification from the outset. Proper estimation of water rates and target environmental conditions should precede the specification of HVAC systems. Latent load, which refers to the moisture content in the air (specifically, how much water is added through irrigation, spraying, and even staff), is a critical factor in specifying HVAC equipment. 

If you don’t know your latent load, be sure to get on the same page as your cultivation director and your HVAC equipment manufacturer. Work together to determine your watering rates and anticipated latent load, and be sure to stick to these specifications once the facility is operational. Dehumidification plays a crucial role in controlling latent load, preventing mold growth and ensuring healthy plant development.

Facility designers and owners must ensure that cultivators understand the relationship between temperature and humidity and how it influences vapor pressure deficit (VPD). Maintaining an optimal VPD is vital for plant growth as it affects transpiration rates and nutrient uptake. Target setpoints for temperature and humidity should be achievable with the specified equipment while maintaining an acceptable VPD range.

Growers accustomed to running cooler room temperatures due to the heat generated by older High-Intensity Discharge (HID) lighting fixtures may inadvertently create conditions that promote bud rot. Targeting 72 degrees Fahrenheit and 50% humidity may sound like a nice, comfortable environment, but most dehumidification units operate below optimal efficiency at lower temperatures (and at lower relative humidity). Raising room temperatures, particularly in LED rooms, can rapidly lower humidity levels, but it's essential to monitor canopy-level temperatures to prevent heat stress on the plants.

To combat humidity issues effectively and maintain adequate air quality, it's recommended that HVAC systems be capable of providing between .5 and 1 air exchanges per minute (30-60 exchanges per hour). Consider adopting a coupled HVAC solution, like Agronomic IQ’s Compressor Wall Grow Room HVAC system that handles both cooling and dehumidification without the need for supplemental dehumidifiers. 

While these systems may be more expensive than a traditional HVAC system upfront, they operate more efficiently and help prevent heat-related challenges in grow rooms because they were designed with the unique challenges of indoor cultivation in mind. HVAC systems should also feature adequate filtration and purification, ideally incorporating HEPA filters and potentially UV sterilization to maintain clean and pathogen-free air.

We recommend utilizing a Horizontal Airflow System (HAF) design, rather than oscillating wall fans. This method of air circulation is commonly used in large-scale agricultural applications. HAF fans are mounted above cultivation lighting and pointed horizontally (and sometimes slightly downward) in a pattern. We love Schaefer Ventilation's Versa-Kool and VK fan lines for our HAF needs. If additional airflow is required, consider adding oscillating fans around the perimeter of the crop, but be aware that the airflow of those fans may interfere with your HAF airflow pattern.

Retrofit Solutions to Control Cannabis Bud Rot

If your cannabis cultivation facility is already operational and experiencing bud rot or mold issues, many of the solutions outlined for new facilities still apply. 

First and foremost, ensure that your system is capable of removing 90-100% of the irrigation water added to the room each day. If your system falls short, consider strategies to reduce water rates or runoff.

If you are still using HID lights, upgrading to LED lighting can significantly reduce your HVAC requirements. LEDs generate less heat, making it easier to achieve and maintain target environmental setpoints. There are also rebates to be had and other cost-reduction considerations for making the switch.

Sometimes the only option left to growers battling humidity is to add supplemental dehumidification. While buying and installing dehumidifiers into an operational grow space can be a costly bummer, there are products that can get your humidity problems under control quickly, and that were designed specifically for the conditions and space constraints found in most grow rooms. 

Quest produces (arguably) the most popular indoor cultivation dehumidifiers on the market, and we recommend their products to growers of all types because of their dependability, efficiency and great customer service. Speaking of efficiency, check out the Quest 335 - the most efficient dehumidifier available to cultivators today, with a capacity of 350 pints per day, @ 8.5 pints per kWh. 

Be sure to keep an eye out for the Quest 225 High Efficiency Series , which will be hitting the market before the end of the year, and boasts a capacity of 225 pints per day, @ 8.2 kWh—as efficient as it gets. While adding dehumidifiers can be a viable solution for combatting high humidity, be cautious of the additional heat load they produce. If your facility already struggles with cooling, adding dehumidifiers may further strain your cannabis climate control system.

Tight plant spacing is another factor that contributes to inadequate airflow and bud rot. Implementing good pruning techniques and removing fan leaves as needed can increase airflow throughout the canopy.

Consider incorporating air purifiers into your cultivation rooms. Products like ProKure, which release controlled amounts of chlorine dioxide gas, can be used to improve air quality and reduce the microbial load in the air and on surfaces. This addition can help mitigate mold issues.

Key Takeaways

Avoiding cannabis bud rot and other mold problems in cannabis cultivation facilities requires careful planning and attention to environmental control measures. New facilities should prioritize airflow, dehumidification and efficient HVAC systems in their designs, while existing operations can implement retrofits and upgrades to address these issues effectively. 

By managing temperature, humidity and air quality, growers can maintain healthy crops and avoid devastating losses due to mold-related problems. In the ever-evolving cannabis industry, staying ahead of these issues is crucial for long-term success. 

If you’re in the process of designing a cannabis cultivation facility and want to ensure you’re taking every precaution to avoid air quality issues, or if your existing operation is experiencing bud rot or other mold or quality challenges, contact Next Big Crop today.

Troubleshooting other aspects of your commercial cannabis facility design? We're here to help—including support in equipment selection, sourcing and financing. Reach out to Next Big Crop today.