How to prevent and control gray mold in greenhouse flowers, and key points for sowing flowers in different seasons
Gray mold is an important disease of greenhouse flowers, mainly damaging the flowers, fruits and leaves. It often occurs along with the flower growing season, especially during the winter and spring greenhouse growing period. If management is relaxed, it further favors the occurrence and spread of the disease, and in severe cases it can cause a large number of fallen flowers and leaves, affect plant flowering and reduce ornamental value.
Pathogen and conditions for occurrence
Gray mold is caused by Botrytis cinerea of the Deuteromycotina subdivision. The pathogen overwinters as mycelium or conidia and sclerotia attached to diseased plant residues, or remaining in the soil. The suitable temperature for the development of this fungus is 10°C to 32°C, with a minimum of 4°C, and the relative humidity must remain above 90%. Because the spring temperature is suitable and the humidity inside the greenhouse is high, failure to ventilate in time is the main reason for the relatively severe occurrence of the disease. Main symptoms of the disease: the pathogen invades through the stomata or wounds of the calyx hairs and flower stalks, then spreads to the fruit stalks; the fruit skin becomes grayish-white, water-soaked and soft-rotted, and when humidity is high a large amount of gray mold forms on the fruit surface. Diseased flowers falling onto the leaf surface easily cause leaf disease, forming large round spots covered with gray mold. Rotten flowers and rotten fruits falling onto the stems cause stem rot, and in severe cases the plant dies. For example, when chrysanthemum leaves are affected, the leaf edges show brown spots and the surface is slightly wavy with concentric rings; the petioles and flower stalks soften first and then the outer parts rot. When fuchsia leaves are affected, the diseased leaves show water-soaked spots that gradually turn dark brown and rot. In addition, Gerbera and cyclamen are also susceptible to damage.
Control methods
1. Seed disinfection. To kill the fungi attached to the surface of flower seeds, the seeds can be soaked in 10% trisodium phosphate solution for 20 minutes, rinsed under running water for 40 minutes, and then used. They can also be soaked in warm water at 52°C for 30 minutes, then dried and set aside for use.
2. Planting in virgin soil. The pathogen mainly overwinters in the soil, so whether for garden planting or pot planting, the soil must be disease-free new soil, and the potting soil, flower pots and bulbs must be disinfected.
3. Greenhouse management. Remove diseased leaves, diseased flowers and fruits, and yellow leaves in time, keep the greenhouse clean, and ensure good ventilation and light transmission. High-temperature greenhouse sealing can inhibit the bacteria. In the early growth stage and after the disease occurs, appropriately control watering and ventilate later at the proper time. Raise the greenhouse temperature to 33°C, as this is unfavorable for the production and differentiation of spores. Reduce humidity to decrease condensation on the greenhouse roof and leaf surfaces.
4. Chemical control. In the early stage of the disease, 45% chlorothalonil smoke agent can be used, or 15% procymidone fumigation for 3 to 4 hours (250 g per mu of greenhouse). 5% chlorothalonil dust (1 kg per mu of greenhouse) can also be sprayed in the evening. For spraying, a 500-fold solution of 65% zineb wettable powder can be used, sprayed once every 10 days, for 2 to 4 consecutive sprays (interval 7 to 10 days). In the early stage of the disease, a 1000-fold solution of 50% procymidone or a 1000-fold solution of 50% duomeiling can also be sprayed, used alternately every 7 days, for 2 to 3 consecutive times, all of which can effectively control the occurrence of gray mold.
5. Reasonable fertilization. Apply fully decomposed organic fertilizer as much as possible, increase the application of phosphorus and potassium fertilizers, improve the disease resistance of the plants, and at the same time pay attention to controlling the amount of nitrogen fertilizer to prevent excessive growth and aggravate the disease.