Tomato
Botrytis Blight
Botrytis cinerea
Fungus
In a Nutshell
- Gray mold on leaves, shoots, fruits or pods.
- Patches of fungal growth on tissues.
- Wilting, browning and damping off of affected plant parts.
- Branches die back.
- Canker formation on woody crops.
Tomato
Symptoms
The extensive growth of mold on leaves, shoots, pods or fruits is the most striking symptom. Initially, sparse, tan-brown and water-soaked lesions appear on plant parts that are in contact with the soil or that have been injured. Numerous hairy and gray-brown patches of fungal growth develop on these tissues. Later on, the mold grows on younger fruits and pods, giving them a fuzzy appearance. Alternatively, the symptoms appear during storage. In both cases, severe losses can be expected. Basal leaf and stem rots cause a total crop failure in the case of susceptible varieties of horticultural crops (damping-off). Occasionally, dieback of branches and canker formation have been observed on woody crops.
Recommendations
Organic Control
Biofungicides containing the competitive fungus Trichoderma harzianum are effective against gray mold on a wide range of crops. Products based on Streptomyces griseovirides are also available for use on lettuce.
Chemical Control
Always consider a integrated approach with preventive measures and biological treatments, if available. Control is difficult to achieve because the fungus may colonize the host plants close to harvest time, thus preventing the application of chemicals that leave toxic residues. In case of early infections, foliar sprays with chlorothalonil can be applied to control its spread. Other fungicides based on fluazinam, and thiophante-methyl can also work. The development of resistance is common when fungicides are used intensively.
What caused it?
The symptoms are caused by the soil-borne fungus Botrytis cinerea, which can grow and infect all plant parts. Moist weather, with frequent rainfall and cool temperatures favors the appearance of the symptoms. The reported optimal temperature range for the development of the fungus, the colonization of the plant and the progression of the disease is 15-20°C. Symptoms first appear on leaves or plant parts that have been injured mechanically during field work or through hail or frost. Lower leaves are most vulnerable. Excessive irrigation and dense canopy may increase the level of the disease by providing a humid, dense environment that is favorable for fungal growth.
Preventive Measures
- Use healthy planting material from certified sources.
- Plant resistant or tolerant varieties of the crops.
- Plant early or early-maturing varieties.
- Keep a reasonable distance between the plants.
- Ensure an adequate row orientation and upright plants.
- Use mulch to impair the life cycle of the fungus and reduce the inoculum.
- Practice good drainage of the location and avoid inappropriate irrigation.
- Monitor the field and remove the decaying plant tissues.
- Take great care not to injure the plants when working in the field.
- Do not over-fertilize the crops.
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