|What causes tomatoes to split open and form grooves at the point where the stem joins the tomato (resembling a star shape)? Almost all of my tomatoes are doing this and although it doesn't affect the taste at all, it does affect the appearance and depending on how deep the grooves get, it reduces the amount of edible tomato.
|What you're describing sounds like Sour Rot, especially if lesions are water-soaked, and may have a white scummy growth in the cracks. Lesions often occur near the stem end scar.
There are a number of fungi that can cause Sour Rot, including Pythium, Phytophtora, Rhizoctonia, and Alternaria.
To control, fruit should be kept off the soil (if possible), and surface wetting should be minimized. (Furrow or drip irrigation is preferred over sprinkler irrigation.)
As a last resort fungicide sprays may be used if you have a "zero tolerance" for defects in your tomatoes. Generally, however, correcting your watering practices is all that's required.