Hi! We've had a large garden for years and have grown a variety of tomatoes. This year we are having a problem with our San Marzanos. They have a fungus, I believe. The tomatoes, before they are vine ripened, are developing black spots that when left get a brownish fuzzy center. Is there any way to save the plants? The only thing we have found on the internet is blossom rot bottom, and it is definitely not that. Any suggestions would be helful!!
This sounds like anthracnose fruit rot. It cannot be noticed on green fruits but becomes obvious on the ripe fruit. These start as small water soaked spots which enlarge and develop dark fungal structures in the center. The fungal centers expand to a quarter inch or so.
The fungal structures overwinter in the soil
As with most fungi once they are seen it is too late to do anything this year. Here are as some practices that can prevent or at least minimize the problem for next year.
1. All tomato refuse should be removed and discarded. It your composter is hot enough they can be composted but otherwise remove off the site.
2. Rotate the crops next year. Plant the tomatoes away from where peppers, eggplants and potatoes were grown in the past three years. They all suffer the same problems.
3. Grow the tomatoes in areas that are not moist, having full sun and lots of air flow.
4. Water early in the morning to allow the plant to dry or with drip watering to keep the water off of the plant.
5. Staking or caging the plants is a way to keep the plants off of the soil.
6. Mulch the plants in the spring with 6 inches of leaf or straw mulch to keep the fungi in the soil from getting in contact with the fruit.
7. Use a preventive fungicide before the fungus is evident. Be sure to read all of the directions and make sure the fungicide is safe for vegetables.
Hope this helps.