Anthracnose Fruit Rot

anthracnose fruit rot

Few discoveries can be as disheartening to the tomato grower as that of the unsightly lesions and large rotten areas indicative of tomato anthracnose.

Untreated anthracnose can cause severe damage and can reduce a beautiful crop of tomatoes to rotten fruit in only a few days so vigilant scouting is advisable to catch this and other diseases early.

Like all fungal diseases, anthracnose is difficult to treat once the plant is infected but there are ways to minimize the damage.

Causes and Symptoms

When tomatoes that are planted in soil that has inadequate drainage, they become especially susceptible to the unfriendly Colletotorichum bacteria that attacks the fruit at every stage in its growth. The disease is usually initiated when insects, birds, or wind infect the soil with the fungus that thrives in moist environments.

The anthracnose fungus can be splashed onto the plant by water that first hits the infested soil or by heavy fruit touching the ground. The roots are also attacked in greenhouse settings because of the aboveground irrigation systems and the warmer temperatures. Any damage from pests such as flea beetles provides an open wound for spores to colonize.

Although infections are not seen on green fruit, as soon as the tomato begins to ripen symptoms emerge as small, somewhat sunken, watersoaked circular spots. The abrasions increase in size, become more depressed, and the center of the tomato darkens, sprouting many small, fungal structures. As the fungus spreads, a semisoft decay occurs, resulting in large rotted areas over time. If the disease has reached this point, results can be devastating.

Treatments and Control

The best treatment for anthracnose is to prevent its occurring in the first place. This can best be achieved by annual rotation of the planting location. Make sure that no non-solanaceous plants such as potatoes, soybeans or peppers were planted in the same soil in the previous year.

It helps to plant only certified, disease free seeds or to soak the seeds you use in hot water for 25 minutes prior to planting. A good layering of mulch around each plant will encourage the water into the ground and away from the stalks and leaves of the plant.

It is important to remove all visibly infected fruit from the vine and discard it. Surviving plants can be treated effectively with a number of fungicide sprays effective for tomatoes. The safest fungicides currently on the market contain the ingredient, potassium bicarbonate. This compound is commonly used in food products and is generally recognized as safe by the American Food and Drug Administration.

The most commonly used organic fungicide for tomato anthracnose is sodium bicarbonate, more commonly known as baking soda. This can be used both for prevention as well as for its treatment. If plants already show powdery mildew, it is best to gently hose down all the infected leaves prior to treatment to dislodge as many of the mold spores as possible.

The same fungicides used to treat septoria leaf blight in tomatoes will also protect fruit from anthracnose. Additionally, fungicides containing small amounts of copper have also been known to successfully treat Tomato Anthracnose.

Comments from Other Gardeners
  • saucelover says:

    Excellent article! I have a couple of questions, though. First, if this occurs, how long can it live in the soil? We practice annual rotation, but only have enough room to have 2 spaces, so we can’t do the 4-year rotation like most people in the know recommend. However, I’d rather not plant them than plant them just to sacrifice them to anthracnose.

    Also, how often should we treat and retreat for either prevention or treatment of this? Thanks in advance! :)

  • Sue says:

    Are tomatoes with anthracnose safe to eat after peeling and removing the lesion????

  • Ron says:

    Ilike Sue’s question. Can one eat this tomato after removing the lesion?

  • Bill says:

    Are infected tomatoes safe to eat?

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