Botrytis cinerea is a significant disease affecting greenhouse-grown flowers, commonly damaging flowers, fruits, and leaves. It often occurs during the growing season, especially in winter and spring, when environmental conditions are favorable. If not properly managed, the disease can spread rapidly, leading to severe losses. In extreme cases, it causes large numbers of fallen flowers, hinders plant flowering, and significantly reduces ornamental value.
The pathogen responsible for Botrytis cinerea is the fungus *Botrytis cinerea*. The fungus survives in infected plant material as mycelium, conidia, or sclerotia, and can also persist in the soil through winter. It thrives at temperatures between 10°C and 32°C, with an optimal minimum temperature of 4°C. High humidity, above 90%, is essential for its development. In spring, when greenhouses tend to be humid and poorly ventilated, the disease becomes more prevalent. The symptoms typically begin with infection through natural openings or wounds on stems, petioles, or flower buds, leading to water-soaked, soft rot. Under high humidity, a gray mold layer appears on the surface of infected flowers, and diseased blooms fall onto leaves, promoting leaf infection and forming circular patches of gray mold. Infected fruits may drop onto stems, causing stem rot and even plant death in severe cases. For example, chrysanthemum leaves show brown spots along the edges, with slight discoloration. The petiole and pedicel become soft and then rot. Dwarf varieties may develop water-soaked, blackened, and rotted leaves. Gerbera and cyclamen are also highly susceptible.
To manage Botrytis cinerea effectively, several strategies should be implemented:
1. **Seed Disinfection**: To eliminate fungal spores on seed surfaces, soak seeds in a 10% sodium phosphate solution for 20 minutes, then rinse thoroughly with running water for 40 minutes. Alternatively, soak seeds in warm water at 52°C for 30 minutes, then dry them before planting.
2. **Soil Management**: Since the pathogen overwinters in the soil, it's crucial to use clean, disease-free soil for both garden and potted plants. Sterilize pots, bulbs, and used soil before planting to prevent contamination.
3. **Greenhouse Management**: Regularly remove diseased leaves, flowers, and yellow foliage to maintain cleanliness and improve air circulation. Avoid excessive humidity by ensuring proper ventilation. During the growing season, control watering carefully, and raise greenhouse temperatures to 33°C, which inhibits spore production. Reducing humidity helps minimize condensation on leaves and structures.
4. **Chemical Control**: At the early stage of infection, apply 45% chlorothalonil smoke or 15% fast smoke for 3–4 hours (250 grams per mu). Alternatively, dust 5% chlorothalonil (1 kg per acre) in the evening. For spraying, use 65% zineb wettable powder diluted 500 times, applying every 10 days for 2–4 treatments. Early application of 50% quick-Ling or 50% Duo Ling at 1000 times dilution, alternating every 7 days for 2–3 applications, can effectively suppress the disease.
5. **Fertilization Practices**: Use well-decomposed organic fertilizers and increase phosphorus and potassium levels to enhance plant resistance. Limit nitrogen fertilizer to avoid excessive growth, which can worsen disease severity.
By combining these preventive and curative measures, growers can significantly reduce the impact of Botrytis cinerea and maintain healthy, vibrant greenhouse flowers.
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