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In this article of
FloraScience, we are featuring Botrytis Cinerea, the most common and serious threat to quality yield of rose and many other ornamentals.
Introduction:
Among the 40 or so diseases reported in roses caused by fungi bacteria, nematodes, viruses and phytoplasmas, botrytis blight or gray mould, caused by Botrytis Cinerea is probably the most common one and always poses a serious threat to quality and yield in roses and many other ornamentals.
Cause of Botrytis:
The most serious damage from this fungus occur in storage or in transit which means that flowers that look perfectly fine at the time of packing turn out to be completely unsalable at the other end, after transport. The fungus can also infect flowers and canes (stems) in the greenhouses. Symptoms are water soaked areas or canes, flower buds that fail to open, specks/spots on outer petals of flowers, blighting of canes, canters etc.
Healthy plants or stock can actually carry the fungus, but the infection develops when environmental conditions are favorable, water humid environments in greenhouses, wet packing materials in the packing/grading halls and cold stores. Very little air circulation and humid and high moisture conditions in shipping boxes.
What is Botrytis?
It is always advisable to develop a preliminary layout by first considering only major activity areas. Points to be taken care of while planning for a greenhouse:
Botrytis fungus is a saprophyte, which means it can survive on decaying plant material and can get easily distributed on crop residues, irrigation water, during harvest and by workers in greenhouses. A petal that has the infection can easily act as a source and spread the disease. Also wounds on plant tissue, pruning points etc are ideal places for the fungus to enter plant tissues.
Symptoms:
In early spring young stalks may suddenly wilt and fall over. Young buds turn black and dry up (Fig. 1). Larger buds that become infected later in the spring turn brown and become covered with a brown or gray mass of fungal spores (Fig. 2). Flowers may fail to open. Usually the stalks below infected buds and flowers are rotted for short distances below the necks. Large, irregular, dark brown blotches may also occur on the leaves. In severe cases, crown and root rot may occur; however, these symptoms are not as common as aboveground symptoms. In wet weather the diseased plant parts soon become covered with a grayish, felty growth of fungus spores. Small, black sclerotia may form on the base of infected stalks or in other invaded portions of plants that have fallen to the ground. The causal fungus overwinters in this sclerotial stage.
Bud and flower symptoms are often confused with injury from the sucking insect, thrips. If thrips are the cause of bud or flower symptoms, these insects can usually be shaken from among the petals onto a piece of paper. The presence of tiny, orange, scurrying insects barely visible to the naked eye is evidence of thrips injury. Thrips do not cause the leaf blotches or stem rot associated with Botrytis blight.
Control of Botrytis:
Control of Botrytis mold is better achieved when several activities are integrated and all of these should be directed towards reducing the inoculums level. All infected buds, flowers and canes in the greenhouses should be pruned and destroyed as soon as the first symptoms appear. Condensation in greenhouses has to be reduced by proper ventilation and air circulation. High relative humidity (more than 90 percent) and free water have to be avoided at all costs in greenhouses, packing halls and cold store areas. Forcing warm air from the bottom of the plants in greenhouses has been shown to reduce sporulation. Proper air circulation among plants by controlling the crop density is also vital.
Research:
Recently, research has concentrated on the use of greenhouse covers that absorb long wave infra red light, which can reduce relative humidity in the greenhouses by slowing down the temperature fall at the end of the day.
Remedies:
Several fungicides have been recommended for the control of Botrytis but it is to be remembered that fungicides can never make up for the absence of sanitation or poor environmental conditions. Also resistance in this fungus to many of the beazamidazole fungicides has been reported. Controlling and preventing gray mold in the greenhouses can always reduce the incidence of this problem during post harvest stages. Protective sprays of Tolyfluanide, Carbendazin, Vinclilozolin, Sprodion and Procymidon have all been used in greenhouse environments.
In packing halls and cold stores, burning chlorothalonil 14% (1 tablet for every 100 Cu. Meters) has proved to be effective. There are newer and more effective fungicides like Decree in the market, but biocontrol and inducing genetic resistance in the variety have been attracting considerable attention. Antagonistic fungi like Trichoderma harzianum have been successfully used. Fungal antibiotics like Bacillus Subtitis, use of antifranspirants that reduce fungal penetration etc are all being tested world over with varying degrees of success. After harvest, growers practice spraying of fungicides to cut flowers, dipping the flowers in fungicidal solutions etc. Harvesting flowers at the correct stage of maturity (older flowers are more susceptible) and storing them at the right temperature and humidity in a clean cold room can avoid many of the problems.
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