Anthracnose: The Tomato Disease You Hope To Never Meet
It took me twenty years of blissful summer gardens to bump into this disease. And truly, I hope you never meet this stubborn, soil-borne fungal pathogen. I can honestly say my life would be no less rich and a little more tomato-y had my ignorance continued indefinitely. And I’d have been perfectly content with that.
But that’s wasn’t my path.
Clearly, we were meant to meet. I’ve more than come to peace with that. If I have had this issue, surely this is a common garden disease that perhaps you have also seen over the year. I’ve worked to learn as much as a I can about this disease I never gave any thought to until last month.
And that’s often how gardening unfolds, a somewhat reactionary process, learning only that which is needed to understand what is unfolding right before you eyes. You may think going into a growing season you know what you need to know for a successful year, then something like this comes along and enlightens you, offering much learning and a deeper respect for growing food.
What It Is
Anthracnose is a fungus, its spores patiently wait in infected soil for up to four years even in our frigid climate until the right medium is nearby. Instead of being an edible mushroom like the fungi you may enjoy eating, these utilize primarily tomato skin as it’s nutrition to form a sunken fruiting body called an acervuli on the surface of your prized summer fruit, causing the tomatoes to rot, the spores to form and explode all over your soil and thus the cycle continues. It can also infect other crops in the Solanaceae family including your peppers, potatoes, and to a lesser degree eggplants. We’ve only observed damage to our peppers and tomatoes this year.
There are many types of Anthracnose, and the name refers to a group of fungi that infect things from oak trees to agricultural crops. Tomato anthracnose is a terrible disease because you don’t know your plants have been infected until the fruit starts to ripen, the exact time when your heart starts to skip a beat or two as your daydreams of a caprese salad are nearly a reality.
How to Identify It
Keep a keen eye on your maturing tomatoes, the large slicing varieties seem to be more prone in my experience to developing this fruit rot. I’ll go a step further and share my observation that my heirloom and open-pollinated varieties were definitely harder hit than my cherries, plum, and paste tomatoes. It has taken all summer for my open-pollinated cherry tomatoes to show signs of it, and my Juliet plum and Sungold cherries remain as healthy as ever. To say it’s a complicated disease is a good start.
It might be confused for blossom end rot, which is a physiological condition not a disease. They may look similar in their later stages, but the fruiting bodies and spores of anthracnose are more brightly colored than the sunken black spots of blossom end rot. Both can occur anywhere on a pepper or tomato, yet blossom end rot is not a fungal disease and as such does not live in your soil. Instead, it is a function of calcium availability in your plant during ripening and is most often seen early in the season when demand for calcium is high for all parts of the plant, and early fruit tends to get the short end of the stick.
What you may see at the earliest stages are sunken spots. Just little sunken spots. I can now recall seeing these but didn’t think too much of them. At first, they are just little divets. But those divets are already working toward producing spores, and are a sign that tomato anthracnose, one of several Colletotrichum species are hard at work reproducing themselves asexually.
How to Manage It
As I said, this is a disease of reaction, not proaction. You won’t know you have it until it is actively producing the fruiting bodies on your precious tomatoes or peppers. However, there are a few things you can do to minimize any chance it could splash up from your soil onto low-hanging fruit. No tomato variety is resistant. This one can attack them all.
Crop rotation is key. You don’t want to plant in the same beds where the infection occurred for at least the following three growing seasons. We have noticed it in multiple beds across our garden, so it is very likely our industrial compost is the cause of infection. I won’t ever know for sure, but in addition to crop rotation, we need to take further measures to minimize a repeat next year.
if you know your garden is infected like we do, mulch is probably the best defense. Mulch provides a barrier between your soil and splashing rainwater, preventing the spores which rely on water as its vector to travel onto your tomatoes or peppers. And it should already be a part of your gardening philosophy, as it is ours. We use compost as mulch, a thick 2” of industrial compost atop our beds each spring.
And that is probably our culprit.
Splashing water from our compost up onto the lowest lying fruit due to now regular torrential rains throughout the growing season provided an easy commute for the spores to infect our largest tomatoes. We have no control over our regular flash floods, and we love our compost mulch, but we will be adding another layer of mulch on top of our compost in our tomato and pepper beds next year.
It may be straw or landscape fabric or leaf mulch, but we will be minimizing any chance that rain could splash soil back up onto our tomato plants. This is our best defense for the foreseeable.
Another really, really important factor is that diseases can also be seed-borne. I know, this sounds crazy weird, but it’s true. So you don’t want to save seeds from any infected plants because the seeds can go on to infect a different bed where you worked hard to rotate your crops. There are home gardening methods for sterilizing seed before sowing, so if you’re a seed saver or swapper, this should probably be part of your best practices before sowing them each winter. It’s a time and temperature thing, exposing the seed to warm enough water for long enough to kill pathogens but not the seed itself.
I have appreciated the learning opportunity this disease provided us. I would not have learned as much about the disease without our outdoor classroom where I was able to continue to monitor and observe how the disease progresses. This is one of those wonders of gardening. As advanced as you become, you remain an avid student and there is always a new lesson or two awaiting you in each new season of growth.