2 common, preventable plant diseases are Blossom End Rot (BER) and Botrytis Gray Mold (BGM).
Prevention and early treatment are key.
BGM is caused by spores and is most likely to happen if plants are in high humidity and poor ventilation. Keep air moving around your tomato plants, and prune heavily. These little brown bud stems are an early indicator of BGM I spotted in my greenhouse. I have disposed of them in my waste bin because my compost pile isn’t efficient enough to hit the temps needed to kill it and I risk spreading in my garden when I do eventually use that compost.
The other disease – BER – is a calcium deficiency and shows up as brown, rotted looking bits of tomato fruit opposite where it attaches to the stem. Calcium is carried by water so BER happens most often if plants are left to dry out or water levels fluctuate dramatically.
It can also be caused by high humidity and low air movement (more common in a greenhouse than on a patio or garden). In some cases it may even be caused by over-fertilizing with nitrogen.
If your tomatoes are in garden soil, be sure to keep ground watered, compost and feed occasionally. If your tomatoes are in a pot, they will dry out faster and need more nutrition than those in the ground (potting mediums are great for drainage but contain almost no nutrients).
Be sure to use a balanced fertilizer and follow the directions on the container.
If you see BER on the fruit, remove it.