Fungal Infection Afflicting Blooms in Greenhouse Flower Plants: Botrytis Gray Mold
Greenhouse growers face a common challenge in managing gray mold, a disease caused by the fungus Botrytis cinerea. This disease is the most prevalent among herbaceous ornamentals, affecting a wide variety of floral crops and other plants.
The fungus thrives in environments with high humidity and temperatures between 32-50°F (0-10°C), making it a post-harvest problem in greenhouses. Symptoms may include pre- and post-emergence damping off, leaf spots, flower blights, bud rots, stem cankers, stem and crown rots, cutting rots, and in extreme cases, plant death.
To control gray mold, maintaining an environment within the greenhouse that will not permit the fungus to grow and sporulate is essential. This includes keeping the relative humidity below 85 percent and avoiding formation of free moisture on plant surfaces. Infected plant material should be removed from the greenhouse and not allowed to sit in trash cans within the house.
Sanitation practices before, during, and after each cropping cycle are the first important steps to achieve good control of gray mold. Under conditions of cool temperatures and high relative humidity (at or above 85 percent), the spores land on the plant surface, germinate, and penetrate the host plant. The fungus prefers to go after the soft, weakened or dead tissues on its host, such as buds, seedlings, and locations where recent cuttings were made.
Small, water-soaked spots are frequently the initial evidence of the infection, which may coalesce rapidly and a large portion of the tissue becomes gray-brown. Necrotic tissues provide an excellent substrate for the prolific sporulation of the fungus, which appears as a fuzzy gray mold when conditions of high relative humidity (at or above 85 percent) prevail.
The fungus produces a large amount of spores that are dispersed in the greenhouse via air currents. If left unchecked, the fungus will grow and sporulate, and the newly produced spores will be the source of infection for other hosts in the greenhouse. Infected seeds may fail to germinate, and young seedlings may wilt or collapse at or near the soil line.
Effective control of gray mold involves integrated cultural practices and chemical treatments. Lowering humidity and improving air circulation to minimize condensation and water films on plants is critical to inhibit pathogen development. Rigorous sanitation, including the removal of dead or dying plant material, is also crucial.
Regarding chemical and biological treatments, Bacillus subtilis shows effective biocontrol activity against B. cinerea. A recent study demonstrated that Bacillus subtilis vectored by Bombus terrestris (bumblebees) can be delivered directly to flowers, reducing infection rates by over 50%, with efficacy comparable to traditional fungicide spraying but without negative impacts on beneficial insects. This entomovectoring method represents a sustainable alternative to chemical fungicides and could be adapted for ornamentals.
Conventional fungicide sprays remain common, but reliance solely on chemicals can promote resistant Botrytis strains; hence combining chemical and biocontrol treatments with cultural controls is recommended. In summary, managing gray mold in greenhouse herbaceous ornamentals entails rigorous sanitation, humidity and microclimate management to reduce infection risk, supplemented by either fungicide sprays or innovative biocontrol treatments such as Bacillus subtilis delivered via bumblebees for effective and sustainable disease control.
Soil hygiene, specifically in the removal of dead or dying plant material, is crucial in controlling the spread of gray mold in greenhouse crops. Moreover, in the realm of health and wellness, adopting integrated science-backed practices such as the use of Bacillus subtilis, a naturally occurring bacterium that exhibits biocontrol activity against gray mold fungus, can contribute to maintaining a healthy and thriving greenhouse ecosystem.
