Many of the things that go wrong with tomato plants, are not disease or insect related. They are primarily due to the plant's growing environment. Problems, such as blossom-drop, cracks in the fruit, blossom-end rot, sunscald, catfacing, and hard spots, occur because of specific cultural, and environmental conditions.
Blossom drop- Many varieties of tomato will not set fruit unless temperatures are between 55°F and 75°F for at least part of the night. Early season tomato cultivars will set some fruit at lower night temperatures, but then have problems as summer progresses, and temperatures soar. If blossoms develop and plants don't set fruit, the blossoms will drop off. Chemicals sprays that supposedly prevent blossom drop can help somewhat, but sprayed fruits often become malformed and seedless.
Fruit cracks- Tomatoes that are growing rapidly can often crack in concentric rings around the stem, especially during hot, dry weather following a rainy period. Mulch tomato plants, and water regularly to prevent rapid fluctuations in soil moisture. Certain tomato varieties are more prone to cracking than others. If your local weather is conducive to fruits cracks, seek out crack-resistant cultivars.
Blossom-end rot- This is a common problem that begins as a leathery patch on the blossom-end of the tomato. Usually the first fruits to ripen are plagued by this rot. It develops when environmental conditions prevent the proper usage of calcium in the tomato plant. When plants are under stress (hot, dry winds and low soil moisture) calcium moves from the roots to the leaves with the movement of water, bypassing the fruits. The lack of calcium in the tomatoes causes tissue to breakdown at the blossom-end. Excessive nitrogen causing very rapid plant growth can also contribute to the condition.
To prevent blossom-end rot from ruining your tomatoes, irrigate and mulch your plants to maintain consistent and adequate soil moisture. Research has shown that applying additional calcium to the soil or spraying a water-soluble calcium solution on the leaves does not remedy the situation. BER is not caused by a shortage of calcium, only the plant's improper use of it, due to stress.
Sunscald- Sunscald can develop as a yellow or whitish patch on the sunward (south-facing) side of a tomato. Affected patches blister, and form a shrunken, grayish-white spot with a papery surface.
Most commonly, sunscald affects small, immature fruits that are suddenly exposed to direct sunlight. This can happen because of insect defoliation (many caterpillars and beetles feed on tomato foliage), diseases that cause leaves to drop, or unsupported, sprawling plants. When fruits are no longer shaded by the leaves, sunscald can occur.
Caging tomato plants provides better foliage cover for the fruits. Controlling foliar diseases, and insects such as the tomato hornworm will help to preserve leaf cover, and keep tomato fruits nicely shaded.
Catfacing- Sometimes tomatoes develop with surface deformations reminiscent of cat-faces or zippers. This scarring of the tomato skin is caused when fruit set happens during cool, cloudy weather. Blossoms stick to developing fruits, causing puckering and scarring. Since this disorder is dependent upon the weather, usually only a few tomatoes are affected in any given growing season.
(Unless of course, cloudy-cool summer weather is the rule for your area.) Large-fruited varieties seem to be much more susceptible to catfacing than smaller tomatoes.
Hard spots- Hard, white spots that develop just under the skin of tomato fruits are caused by plants in stress. Too much water, too little water, and high daytime temperatures (in excess of 90°F) can all be contributing factors. Tomato plants cease to produce red pigment during periods of extreme high temps, causing tomato flesh to develop with a colorless cast to it.
Again, minimizing stress to the plant by mulching, and watering regularly can go a long water to preventing hard spots from developing in your tomatoes. When ultra-high temperatures are predicted, shade cloth, or screening, properly placed can ease the heat during the hottest time of the day.
- Mary Vaananen