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What to do about tomato anthracnose or fruit rot

This tomato shows the typical "spots" of tomato anthracnose.
This tomato shows the typical "spots" of tomato anthracnose.
Kim Willis

A common tomato problem is really prevalent this season. Many people call it fruit rot but the culprit is tomato anthracnose (Colletotrichum coccodes). Tomato anthracnose is one of those nasty fungal diseases that are so hard to control. This disease also affects the leaves, stems and roots of tomato plants but it’s the infection of the fruit that is most problematic. The disease frequently begins in late summer, and early fall with temperatures over 80 degrees and rainy weather being prime anthracnose weather.

Tomato’s that are ripe or nearly ripe develop what is called “watersoaked” spots, sunken, shiny areas with a number of small black spots in the center that eventually create a large black spot and the fruit rots around and under the lesion. The black spots produce salmon colored spores which can infect other fruits around them. When you cut a tomato with anthracnose you often see a black area on the meat inside below the outer spot. The rotted spots may also grow a secondary fungus; gray, fuzzy mold if left long enough. Tomatoes can have one spot or several.

Green fruits often have the fungal spores on them but the disease isn’t obvious until tomatoes begin to ripen. If your green tomatoes have large rotted areas and your tomatoes plants look blackened and wilted you may have the more serious problem of late blight. Late blight will quickly kill all the tomato plants in your garden.

Tomato anthracnose also makes the lower leaves on the plants get yellow spots with a tan center, and they eventually wilt and turn gray-brown. The stems may also develop spots. These foliar symptoms are very similar to other fungal disease of tomatoes and tomato plants can have more than one fungal disease going at the same time. In fact diseases like early blight weaken the plant and make anthracnose more common.

Tomatoes vary in how susceptible they are to “fruit rot”. At any time you may have some tomatoes with the spots and some without, even on the same plant. Your plants won’t die from the disease, although the disease often combines with other tomato fungal diseases to limit production and make the plants look horrible. Plants without many leaves don’t have the sugars and other nutrients that make fruit tasty and you may notice the tomato’s flavor isn’t as good.

You can cut off small rotted areas and eat the fruit without problems but if you like to can tomatoes you may have a problem. Tomatoes with anthracnose often cause bacterial problems in canned products resulting in spoilage. Don’t use any fruit with rotted spots for canning. It’s not wise to use them in frozen products such as tomato sauces either. Ripe tomatoes without rotted spots, even if you know anthracnose is around, are safe to use.

Prevention and control of anthracnose

Anthracnose can be prevented with fungicide sprays started as soon as there is fruit on the vine. Homeowners can use sprays with chlorothalonil (Daconil) or fungicide sprays with copper. Check the label to see if the product says it controls anthracnose and follow label instructions for use. If you have had problems with anthracnose in previous garden seasons a preventative spray program is a wise move.

Like other fungal diseases mulching and keeping plants off the ground by staking or tying them helps. Good airflow is important so don’t crowd plants. Some weeds harbor the disease so keep your garden weeded. Water at the base of the plant and try to keep plant foliage from getting wet. Tomatoes require well drained soil and wet soil often results in bigger problems with fungal disease.

If you get anthracnose in the garden it’s very important to remove all tomato plant debris and rotted fruits to a separate, remote compost pile or to plastic trash bags and the landfill. The fungus spores overwinter in tomato debris. And rotate your crops! This disease can also live in the soil through the winter and infect your plants next year.

Don’t allow your fruits to get over ripe on the vine. Pick them while red and still firm if you suspect you have anthracnose in the garden. Discard tomatoes with the rotted spots away from your garden, not in the compost pile either. If you pick tomatoes and notice small rotted spots cut out the spot and use them at once or toss them as they will quickly rot.

When storing tomatoes for fresh eating for a few days, try to put them in a single layer, not touching each other until used. If one has anthracnose that you didn’t spot it is less likely to spread to the other fruit if they don’t touch. And tomatoes should not be stored in the refrigerator! It ruins the flavor and they will actually spoil faster.

Tomatoes are not the only plants that get anthracnose. Peppers, eggplant, potatoes, cucumbers, strawberries, some squash and pumpkins also get anthracnose. Some of these strains of anthracnose can “crossover” especially in closely related species like tomatoes and peppers.

Even if some of your tomato fruit gets anthracnose late in the season you may still get enough good fruit for eating and cooking. Next year you may want to begin preventative sprays early in the season.

Here are some additional articles you may want to read.

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