Sounds like botrytis blight, or gray mold. This is a wide ranging fungus disease that attacks over 200 kinds of plants, including tomatoes. If that’s not frustrating enough for gardeners, botrytis can also cause a variety of diseases, from damping off to blights of stems, buds, fruits and flowers.
How Does Gray Mold Affect Tomatoes?You’ll often first see symptoms of gray mold on tomato stems, as dark spots or girdling. Actually, you’ll probably miss these symptoms totally unless you’re looking for them.
Once gray mold takes hold, it can spread to all parts of the plant. The immature fruits may turn a light brown or whitish color, with the inside flesh getting soft and moldy. The instance here shows the stem end slowly rotting and falling from the stem.
What Can You Do About Gray Mold?Unfortunately, there are no tomatoes with resistance to botrytis. Fungicides can help prevent it, but they will not cure a plant that is already infected.
About the best you can do is remove and destroy the affected plants and fruits and to a preventative spray of any healthy looking plants with a fungicide labeled for use on edible plants. Something like anything with copper or sulfur, neem ore various other organic fungicides are good.
Next season, be sure to rotate your crops. Botrytis spores are good at overwintering in the area. If you have similar weather conditions again, high humidity or damp, cool nights, you may want to consider a preventative spray early in the season, with your organic fungicide.
Then be on the lookout and remove any plants that show signs, as soon as possible.