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What is it?
Tomato anthracnose is caused by gloemerella phomoides, a fungus. It primarily infects ripe tomato fruits, rotting them, but can also infect unripened green tomatoes in the vegetable garden. However, tomato anthracnose occurs most often on tomato plants which are fully ripened and lay close to the ground or soil level.
What does it look like?
Glomerella phomoides damage shows up at first as water-soaked spots on the surface of the tomato fruit. These areas will usually have a lighter brown center, getting darker toward the outer edge. Sunken areas of anthracnose on tomato fruits typically grow up to one half inch in diameter and will form a series of concentric rings within the sunken, affected spot of anthracnose. These sunken spots may darken brown over time and will eventually become blackish. The anthracnose water-soaked spots may also merge together and result in the anthracnose covering a large portion of the tomato fruit. In tomato plants, typically only the tomato fruits itself is affected by the anthracnose, and it is there you will find these visual clues to the problem. Unlike other vegetable plants, tomato anthracnose does not typically attack the leaves of stems of tomato plants.
How does it manifest?
Coletrotrichum lagenarium is primarily present in regions where the temperature remains around 70° to 80°. Anthracnose also thrives in areas that have frequent, regular rainfall. Anthracnose can attack all above ground sections of the plant including the fruit itself, the stems and the leaves. It is very destructive to these plants in a quick period of time and the plants will die off quickest when the weather is most humid as this is when the fungus spreads rapidly. Once plants have been infected the spores can overwinter on plant debris and seeds that were left in the garden. Then when spring rains arrive the splashing water quickly spreads the coletrotrichum lagenarium to new, previously healthy plants. Anthracnose can also be spread by feeding cucumber beetles as well as garden tools, gloves and on shoes or clothing which may then come in contact with plants after touching an infected one.
What can you do about it?
Chlorothalonil containing fungicide is effective in controlling the spread of the disease if applied when you first notice signs of damage. However, you may need to repeat applications of the fungicide several times as seven day intervals before you contain the disease and rid the plants of the fungi. Plants may become reinfected if you have not killed off all of the fungus and the weather becomes warm, wet and humid again as these are prime conditions for spread of anthracnose. You can safely repeat applications of a chlorothalonin insecticide to tomato plants at weekly intervals right up until you harvest your tomato fruits, Additionally, there are varieties of tomato plants which are resistant to the disease that can be planted. After the harvest of tomato fruits, you will want to diligently clean up and destroy all plant debris to prevent further spread of the anthracnose to other regions of the vegetable garden.
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