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What is it?
Anthracnose is caused by coletrotrichum lagenarium, a fungus. It primarily infects cucumbers, watermelons, and muskmelons and is the predominant killer of these plants in the United States. Anthracnose does not affect the squash or pumpkin members of the curcurbit family.
What does it look like?
Coletrotrichum lagenarium damage shows up at first as yellowish areas on the leaves and melons which appear water-soaked but quickly dry out and turn brownish. These areas start quite small and spread in size rapidly. Once the areas dry out they crumble into a hole which looks ragged as if shot by a gun. Watermelon plant leaves turn black rather than brown, however all affected curcurbit plants may have elongated spots which appear on the stems. These areas will usually have a lighter brown center, getting darker toward the outer edge.
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 or if you get an infestation of cucumber beetles as these are prime conditions for spread of anthracnose. Additionally, there are varieties of these curcurbit family plants which are resistant to the disease that can be planted.
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