What’s that black mold inside my tomatoes?

While slicing open recently harvested paste tomatoes for dinner last night, I found black mold growing inside the next-to-last tomato that I was going to use.  I was surprised because there was no sign of a problem on the outside of the tomato.  The next tomato had it too.  I frantically searched through the tomatoes I had already cut up, but they seemed OK.  Hopefully, the tomatoes that were already cooking were good.

tomato26

An internet search turned up the most likely culprit:  anthracnose.  More information about this disease is available from the Missouri Botanical Garden, Cornell University, the Ohio State University, and the University of Minnesota.  Anthracnose can also infect other vegetables including peppers, eggplant, beans, squash, and cucumbers.

Anthracnose isn’t considered to be very serious.  It can be prevented through crop rotation (which I already practice), maintaining good drainage (not a problem with raised beds), and by leaving space between plants so that they can dry out (OK, that’s a problem with my tomato jungle).  It’s also important to remove old tomato vines and diseased fruit and to not use overhead watering as that spreads the disease.

You might be tempted to spray fungicide on diseased plants, but once a fungus shows up on a plant, it’s probably too late.  Fungicides can prevent the spread of fungus, but they usually can’t get rid of the fungus once it’s infected a plant.

tomato jungle

tomato27

health kick paste tomatoes

tomato28

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About brianbreczinski

work: chemist, NMR manager; hobbies: gardening, reading, photography, electronics, biking, woodworking
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12 Responses to What’s that black mold inside my tomatoes?

  1. Ophelia says:

    I like the helpful info you provide in your articles. I will bookmark
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    I am quite sure I’ll learn many new stuff right here! Best of luck for the next!

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  4. I haven’t come across this problem in my tomatoes, but if and when I do, I know where to look for advice!

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  7. Sue says:

    I had the same problem on my huge beautiful tomatoes-After reading your post I guess I shouldn’t crowd them

  8. Sue says:

    Hi. I know this is an older post, but that damage looks like it could be Internal Blossom End Rot, especially given the variety, as elongated paste tomatoes are particularly prone to BER. It’s a form of blossom end rot that happens not on the outside end of the tomato but inside the tomato hidden from view, caused by the same problem (calcium transport problems within the plant while fruit is developing). Damage typically looks like what’s in your photo.

    • It could be that, or a couple of other types of fungal problems, but when I posted this anthracnose seemed the most likely. I don’t think I was seeing blossom end rot in my tomatoes at the time, so I decided that wasn’t the problem. I’ve certainly had BER problems with my tomatoes, usually when I couldn’t keep soil water levels fairly constant.

  9. Dean says:

    Can I cut off the bad and eat the rest?

    • I’ve done that with small mold spots, such as blossom end rot, but in this case I think I actually discarded the tomatoes. If the mold is anthracnose, based on what I read about it (see the links in the blog post) it should be OK, but other molds may be dangerous and there may be parts of the mold growing in the tomato that you can’t see. Even if it doesn’t make you sick, it probably won’t improve the flavor.

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