Question: My tomatoes are experiencing some problems. Some look like they are rotten on the bottom, some are cracked, and some have yellow blotches on them and are inedible. Can you help me identify what causes these conditions and what I can do to prevent them in the future?
Answer: After waiting all season to enjoy vine-ripened, homegrown tomatoes, it’s so disappointing to find some of them look disfigured or ruined.
I will address five common tomato problems that we see a lot in the Master Gardener Plant Clinic.
- Blossom end rot in the tomato fruit is indicated by a dark, leathery, sunken area at the base or flower end of the tomato. The most common cause of this is uneven watering, resulting in the plant unable to take up calcium. Excessive cultivation around the roots, burning from improper fertilizer application, or too much fertilizer containing ammonia can also cause blossom end rot. To avoid this malady, maintain even soil moisture by watering regularly during the dry growing season and mulching the plants to retain moisture. Get a soil test to make sure your soil has a pH of 6.5-7. Use a fertilizer high in superphosphate but low in nitrogen. You can also apply a calcium foliar spray, available at garden centers, enabling the plant to uptake calcium through the leaves.
- Catfacing shows itself as a deformity that occurs when the flower is forming and is also on the blossom-end of the tomato. Cold temperatures during flowering, improper pruning and high applications of nitrogen can cause this. Large-fruited varieties such as “Brandywine” are more prone to catfacing than others. The tomato with catfacing is still edible — just cut out the deformed area.
- Circling cracks and cracking at the stem end of a tomato are caused when the inside of the tomato grows faster than the skin, so it splits. Causes are over-fertilization, extreme fluctuations in moisture and soil temperature and not enough leaves to protect the fruit. Some tomato varieties are more susceptible to cracking.
- Stink bug damage, known as “cloudy spot”, shows up on a tomato with white or yellow pithy spots and mottling over the surface of the fruit. Stink bugs insert their needle-like mouth parts into the fruit, sucking out the juices, leaving hard, inedible areas on the tomato. Stink bugs overwinter in weedy areas, so control weeds around the tomato patch. They are difficult to control, but can be hand-picked or vacuumed up and dropped in a pail of soapy water. In larger gardens, try kaolin, an organic, white, edible clay sold in garden centers or online under the brand Surround WP. It coats the plants and fruit in a white film, thus deterring the bugs, then is harmlessly washed off before harvesting.
- If your tomatoes have a whitish blotch extending over one side of the fruit, it might be that it was exposed to too much direct sunlight, causing sun scald. Try to ensure there are enough leaves to shade developing fruit or use sunshade fabric (available at garden centers) during days of intense sun and high temperatures.
These are just a few tomato troubles. If you have others, email, call or visit the Douglas County Master Gardener Plant Clinic at douglasmg@oregonstate. edu, 541-236-3052, or 1134 SE Douglas Ave., Roseburg.