Blossoms falling off, blackened

by Mike
(Auburn, CA)

Q. I just planted my tomatoes, so this is a preventative question. Last year I had a problem with blossoms turning black on the stem right beneath the flower and then falling off. What can I do to avoid this this year as my plants mature?

A. From your description, it sounds like the culprit is bacterial speck. As the name implies, it's caused by bacteria (Pseudomonas syringae pv. tomato) that can overwinter in the soil or transmit on seeds. Bacterial speck can appear on any plant part. It thrives in cool weather, so if you had a wet spring last year, those bacteria were loving life on your tomato plants.

Leaves on infected plants will also (eventually) show brown or black irregular spots surrounded by yellow halos.

You can control bacterial speck by avoiding excessive watering. Naturally, you can't control the rain! Also, begin a systematic spraying program using a copper spray. Apply each week and after rain.

Take these additional measures to minimize the risk of tomato blossom drop.

Good luck and happy gardening!
Your friends at Tomato Dirt