Anthracnose can cause serious losses in tomatoes and lettuce
Anthracnose is caused by the fungus Colletotrichum phomoides and is a common and widely distributed rot of ripe tomatoes. The disease can cause serious losses after the product is harvested. In lettuce it is caused by Marssonina panattoniana (Berl.) Magn.
Symptoms of Anthracnose
Infected fruits show a small, slightly sunken water soaked circular spot which become about 30-40mm in diameter. They become darker and more depressed with time and often have concentric ring markings in the inside of the sunken area. The centre if the depressed area can become light in colour and during humid periods masses of spores can erupt through the surface of the lesion or along the sides of cracks in the depressed areas. The spores have a characteristic salmon colour. During warm weather conditions the Anthracnose fungus penetrates deeper into the fruit and renders the fruit unmarketable.
Anthracnose persists form season to season on infected plant refuse in the soil. The initial fruit infection sometimes may come from infected leaves, but most fruits probably are infected from conidia (spores) produced in the soil.
On lettuce leaves the disease can be identified by small, pin-point, water soaked lesions which enlarge to reddish coloured circular to angular spots. These spots can be up to 4 mm in diameter. The midrib can also be infected after which the leaf may break off at the infected point.
Anthracnose is prevalent in areas where there is poorly drained soils. The fungus can live from season to season and no varieties are 100% resistant. Sprays such as mancozeb etc. will control the fungus.
The less rotten fruit found in and around a greenhouse building the less anthracnose will be a problem. This applies to other crops such as lettuce, brinjals and peppers. Unmarketable fruit should be discarded in such a way that the spores cannot reach the greenhouse. It is even a good idea to either burn or cover old leaves as well. Any leaf lying around on the floor is infected with various spores and bacteria that feed on it. These spores are very light and drift in the air to infect the next host. So, keep your production area clean and you will find a remarkeble reduction in spore infected diseases.