Bud rot is a destructive plant disease that targets the dense floral clusters and buds of various crops, often leading to significant losses for growers. This condition causes the rapid breakdown and decay of plant tissue, making affected parts unmarketable and sometimes destroying entire harvests. The disease progresses quickly once established, transforming healthy buds into masses of rotting material. This swift, localized destruction is a major concern in agriculture and horticulture, particularly in environments where plants are grown in close proximity.
The Primary Fungal Agent
The organism responsible for bud rot is the ubiquitous fungus, Botrytis cinerea, commonly referred to as Grey Mold. This pathogen is a necrotrophic fungus, meaning it actively kills host cells to absorb nutrients from the dead tissue. It is opportunistic, existing widely in the environment and attacking a vast number of plant species, including fruits, vegetables, and ornamentals.
The fungus survives and spreads primarily through its asexual spores, known as conidia. These microscopic spores are produced in massive numbers on infected tissues, giving the diseased area a characteristic fuzzy, grey appearance. The conidia are lightweight, allowing them to be carried easily by air currents and deposited onto healthy plants, initiating new disease cycles.
Critical Environmental Triggers
The transition of Botrytis cinerea from a dormant spore to an active infection depends on specific environmental conditions. Prolonged exposure to moisture is a primary trigger, as the conidia require free water (dew, rain, or condensation) to germinate and penetrate the plant surface. Infection is strongly favored by high relative humidity levels, generally above 60%, and extended wetness duration.
Stagnant air within the plant canopy significantly contributes to the problem by preventing moisture evaporation. When plants are densely packed, a microclimate of consistently high humidity forms around the buds and leaves. This lack of air exchange sustains the moist conditions required for the fungus to transition into an actively growing infection structure.
While the fungus can survive in a wide range of climates, its optimal growth occurs within moderate temperatures. Botrytis cinerea thrives in temperatures between 60°F and 75°F (15°C and 24°C). This temperature range, combined with high humidity and limited airflow, creates the ideal scenario for the pathogen to rapidly colonize plant tissue.
How Infection Takes Hold and Spreads
Once the environmental triggers are met, the fungus begins its invasion of the dense floral tissue. Botrytis often requires an entry point, typically exploiting weakened or damaged areas like wounds from pests, mechanical handling, or the natural senescence of flower petals. The fungus then secretes enzymes and toxins that break down the plant’s cell walls, allowing it to grow internally within the bud structure.
The infection starts deep within the dense cluster, manifesting as water-soaked, browning, and softening tissue that is initially hidden from view. This internal decay progresses quickly, leading to necrosis and a mushy texture in the core of the bud. As the fungus consumes the dead tissue, it produces its own reproductive structures.
The final stage involves the production of a new mass of grey-brown conidia on the surface of the rotted tissue. When an infected bud is disturbed or exposed to a slight breeze, these spores are released as a cloud of infectious particles. This secondary spread allows the disease to jump to neighboring healthy buds, leading to a rapid epidemic across the crop.