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Botrytis, also known as gray mold or bud rot, is an extremely common humidity related disease, found in greenhouses around the world. With over 200 known species, this fungal pathogen affects most fruits and vegetables, as well as ornamentals and cannabis. Preventing botrytis is key for many different agricultural sectors.
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Botrytis’ Effects and Symptoms
Gray mold begins when the botrytis cinerea fungus infiltrates the plant, through soft tissue or wounds. It develops inside the plant, eventually erupting on almost any part of the plant: leaves, stems, flowers or fruit.
Though symptoms vary, they generally involve darkening and softening of the tissue on which it erupts. In later stages, spores begin to emerge in the form of white or gray fuzz. Eventually, gray mold will cause its host to dry out, shrivel and rot.
Preventing & Controlling Botrytis
When it comes to indoor or greenhouse diseases, preventing botrytis is often much simpler and more cost effective than treatment. By the time symptoms become apparent, the disease has already taken hold, drastically reducing the efficacy of treatment methods. Additionally, there are currently no proven non-fungicidal remedies for gray mold.
In order to develop spores, botrytis requires specific climate conditions, including relatively cool temperatures and high levels of humidity. When the conditions are right, spores begin to develop. They are then easily carried by wind, transported by people or thrown around by splashing water, making it very difficult to control their spread.
Once relocated, the spores need to germinate and infiltrate the plant, in order to do any damage. Germination is only possible where there is free water, meaning a wet surface. Denying the fungus its preferred conditions is the key to preventing botrytis. There are many different greenhouse climate control methods. A grower’s best bet is to utilize a mixture of all measures.
Avoid water presence
One of the most basic requisites for botrytis to spread is water, without which spores aren’t able to develop.
Irrigating properly, straight to the soil while avoiding the leaves, will drastically decrease the presence of water and inhibit germination.
You should also water during morning hours, to allow crops to dry in the sunlight.
Not all water comes from irrigation. Plants constantly perform transpiration, and water evaporates from the soil. All this water vapor is contained in the air, in the form of humidity. When humidity builds up, it begins to condense on colder surfaces, such as railings, various structural elements, or even the leaves themselves. Even if condensation is avoided, high levels of humidity on their own are enough to initiate germination.
Maintaining lower relative humidity levels and eliminating the threat of condensation, with the use of dehumidifiers, is one of the most basic methods to combat botrytis, as well as other fungal diseases.
Prune and don't overcrowd
In a crowded ecosystem, with dense foliage, water vapor has a hard time dispersing, creating pockets of very high humidity surrounding the plants. These pockets are known as boundary layers. Spreading out the placement of plants will allow more air to flow through the canopy, reducing humidity build-up.
Pruning overgrown plants may also help in creating a less crowded environment. Its important to disinfect any equipment when going from to plant, as any contact can carry spores and infect additional plants.
Increase air circulation
IAnother way to reduce humidity and improve plant health is by incorporating air circulation. Any movement of air can help in dispersing the boundary layers. But while most airflow schemes are sporadic, creating differing climate conditions in different areas, air circulation is a thought out, circular system.
A botrytis breakout anywhere in the greenhouse may lead to a rapid infection of the entire space. Proper air circulation helps in homogenizing the greenhouse climate conditions, decreasing the chances of humidity building up in a certain area.
Keep soil clean
Good greenhouse stewardship is always a good thing. Debris in the form of leaves or fruit which fall to the ground quickly begin decomposing, providing the perfect platform for diseases, such as botrytis, to take hold, develop spores, and disseminate through the greenhouse.
In the case of fungal diseases, maintaining a clean unobstructed soil bed is even more crucial. Spores may travel in water, even in small splashes. Any material on the ground increases the danger of dripping water, by causing it to splash, throwing spores around and infecting nearby plants.
Avoid wounding plants
Botrytis begins its journey by attempting to infiltrate plants, and any wound can provide the entry way. It’s extremely important, when tending to the crop, to be careful not to injure the flesh of the plant, making it difficult for infection to occur.
Maintain proper radiation
Radiation, whether in the form of sunlight, or artificial light, assists in evaporating any free water which may find its way into the greenhouse, making it another tool for combatting humidity.
But radiation isn’t just about drying. A proper lighting scheme will improve plant health, metabolism and photosynthesis, strengthening the plant and improving its immune system. This can help in preventing any disease, by lowering the susceptibility of the crops.
Apply neem oil
Neem oil acts as a natural fungicide, and can help reduce the concentration of fungal spores.
Applying neem oil regularly, as a preemptive measure, can drastically reduce the chances of a botrytis breakout. It also provides the added benefit of acting as a natural pesticide, decreasing harmful insect populations in the process.
It’s possible to make homemade neem oil spray, by mixing 1-5 milliliters of neem oil, 1-2 milliliters of liquid soap and 1 liter of water.
Neem oil can be found in most health stores, and is unharmful to humans.
Remove infected plants
Removing any plants which may have been infected is the last tip and last resort when it comes to prevention. It is critical in stopping the spread of an already active outbreak, though it is preferable to avoid this situation in the first place.
Any discarded plants should be removed from the space immediately, in order to stop the spores from spreading.
Infected plants should not be composted, as the spores remain active and may cause future outbreaks.