Powdery Mildew Prevention

Powdery mildew is a fungal disease that can affect a wide range of plants. It is one of the most common and costly diseases for nursery plants such as flowers, vegetables, woody plants and cannabis. It can infect plants under a wide range of conditions making it challenging to prevent and combat. Temperature, relative humidity, light, and air circulation are all prominent environmental factors that influence powdery mildew and its prevalence. Once it becomes active on a contaminated plant, powdery mildew will leach away a plant’s nutrients, making the plant weaker and bloom less, ultimately reducing yields. Prevention is the strongest approach you can take against powdery mildew.

Integrated Pest Management (IPM)

IPM as a concept was first developed in the late 1950s out of concern for the environmental impacts of the heavy and widespread use of pesticides. It is a layered, ecosystem-based approach that focuses on long-term prevention of pests through biological controls, physical habitat management, modification of cultural practices, the use of chemical controls (more often though it seeks to employ alternatives to synthetic chemicals), and the use of resistant plant varieties. IPM is all about taking actions before there is an issue to keep pests and contaminants from becoming a problem.

Proactive Rather Than Reactive

Monitoring is arguably the most important preventative measure of IPM. Not only does it help provide information specific to a current grow that can better inform a growers decisions, it also enables early detection. Routine scouting as part of a structured crop inspection program is an essential practice. This entails examining the upper and lower leaf surfaces, noting and then recording any irregularities and colorations to better detect any changes.

Culture controls refer to sanitation, weed control, environmental factors such as light/temp/humidity, and the use of powdery mildew resistant plants. While cleanliness alone will not guarantee pest and disease problems won’t happen, it is a foundational piece of IPM that will make all other prevention methods even stronger. Common cultural control approaches include:

  • Removing dead/dying plant matter, getting rid of crop residues, and washing and disinfecting all tools and equipment are just a few of the habits important to practicing good sanitation. Clean room principles can dramatically bolster your IPM plan, which is discussed in greater detail further down this article.
  • Removing all weeds from inside your greenhouse (or indoor growing environment) and from the areas immediately around the outside can reduce pest habitat.
  • Management of temperature and humidity (or more importantly, Vapor Pressure Deficit <link to VPD section in PM #1>) is especially important for preventing and controlling powdery mildew.
  • Maintaining good drainage to avoid any standing water is an important and often overlooked environmental control. Even if a grow space is not currently being used, keeping it clean and sanitized is important.

Choosing to grow plants with genetic resistance to powdery mildew and other pests/contaminants can give you a leg up in preventing and managing infections. Additionally, biocontrol (using living organisms to combat pests) can be an important component of IPM, especially with the development of pesticide resistance. It cannot stand alone however and requires the support of other IPM strategies in order to be effective.

We offer a possible paradigm shift in regards to the creation of clean grow environments and current IPM strategies. Part of the underlying theme of IPM is around controls and preventative measures. However, the current foundation exists around these individual measures acting in parallel to ensure a safe grow. We propose that these processes should be layered with an underlying foundation of creating or retrofitting facilities with clean rooms and clean room techniques, with the remaining IPM solutions built on top of this core foundation. This cost effective change refocuses growers time and energy on establishing proper plant health for increased yields, reduces the need for chemical applications, and minimizes crop risk.

Clean Room Principles

One tends to think of airlocks, air showers and full body suits when thinking of cleanrooms. While these tactics can benefit an indoor growing environment and be vital in certain scenarios, they are not required for growing environments. A cleanroom is simply defined as a “room with a defined concentration of airborne particles, designed and used in a way that the number of particles introduced into the room or originating and being deposited in the room is as small as possible, and in which other cleanliness-relevant parameters such as temperature, humidity and pressure can be controlled as required.” (VDI 2083-1) The foundation of cleanrooms is air filtration and circulation. Incoming air is filtered and rooms maintain constant airflow, ultimately pushing air towards filters that will continuously scrub the air of contaminants.

Air Filtration and Circulation

The smallest objects that the unaided human eye can detect is anything larger than about 4 microns (0.1 mm). Powdery mildew spores are sized between 1 to 3 microns and a room filled with PM spores from a plant is largely undetectable using non-sensor based monitoring systems. The value of creating a clean environment is to prevent powdery mildew from taking hold, or if after the fact, to mitigate the population and halt the spread of active powdery mildew spores.

Best practice for creating a clean room is to have the entire volume of air scrubbed through a high quality air filtration system once every 10 minutes with filters capable of capturing small contaminant sizes. With proper airflow management where clean air is directed from the top of the plant canopy down to the floor, the spread of powdery mildew spores is greatly reduced and surrounding plant contamination slows. This top-down method of moving air also helps maintain even plant temperature from the top of the canopy down to the root structure.

Beyond Powdery Mildew

A study published in 2017 by researchers at UC Davis found multiple bacterial and fungal pathogens in medical marijuana products from California. 90% of the samples had something on them. While strong immune systems can typically withstand repeated exposure to these pathogens, individuals with immunocompromised systems (cancer patients, AIDS patients, etc.) face serious outcomes when exposed, especially when these pathogens are introduced directly into the respiratory system. Immunocompromised individuals are the predominant medical marijuana users, making this is an issue of critical importance and the need for the creation of clean product a life and death issue.

Airborne fungal spores and toxins in cannabis can also pose a risk for workers and processors. A 2017 report published by the CDC highlighted exposure risks to airborne fungal spores and toxins in an outdoor cannabis growing operations. Findings suggest concern for long term exposure to Actinobacteria and fungus in these environments as people working in them are at increased risk for respiratory issues. Previous to the CDC report, the US Department of Justice found that exposure to and risk of respiratory issues would likely be greater in an indoor growing environment.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) reaffirmed in 2018 that porous media particle filtration systems (mechanical filters) remain the only systems proven to provide significant health benefits. It is crucial not only for the health and viability of your crops to maintain a clean growing and processing environment, but also for the health of your customers and employees. Air filtration is a foundational step in accomplishing this. Adopting cleanroom principles and technology can help your crops thrive and truly benefit those who work with and consume what you grow. It can also put you a step ahead in meeting regulation standards currently enforced and those to come.

The Golden Rules for a Clean Facility

  1. Don’t let contaminants into your facility.
  2. If contaminants do enter the facility, control where they go and how they are captured.
  3. Clean facility design is a niche engineering trade that focuses on the creation of clean zones with a person or product moving from the dirty exterior through isolation zones before entering the cleanest growing or processing zone. Each zone is meant to be cleaner and more positively pressurized than the previous zone. This helps push contaminants away from the cleanest grow room or processing center.

Learn More – Defend with Prevention

Within 30 minutes of runtime, the E1 Air Filtration unit can scrub a 2,000 sq. ft. room of 98% of all powdery mildew and contaminants 0.3 microns or larger. The E1 empowers growers and processors to instantly create and indefinitely maintain clean environments. Unlike devices that rely on photocatalytic oxidation (that rapidly degrades – requiring replacement – and are quickly rendered less effective via the buildup of dirt and dust) and Ionic Oxidation (the levels hydrogen peroxide emitted via devices that offer periodic misting of areas is not at a level to provide sufficient or even moderate sanitation results), the E1 Air Filtration Unit captures and retains airborne contaminants and can be washed down and sterilized inside and out. This means you can use it with complete confidence that it is not a source for spreading disease. Contact us today to learn more about how the E1 Air Filtration unit can be a first line of defense in your integrated pest management plan.