Tomato sunscald, uneven ripening and cracked fruit

This season has compelled us to consider, in this space, some of the ills of home garden tomato production. These have included tomato spotted wilt virus, poor fruit set, and early blight. Other challenges include cracked fruit, sunscald, and uneven ripening.

Cracked fruit have circular cracks, also called growth cracks, on the top (stem end) of the fruit. Sometimes these cracks go deep into the fruit, causing it to rot. Cracking is more serious during a period of drought followed by heavy rains or heavy irrigation, which encourages rapid fruit growth, disallowing slow, even ripening. Much more of a problem during hot weather, cracking is observed after the fruit has reached full size and begun to change color. Though unsightly, cracked fruit is edible. Some varieties are more susceptible than others to cracking. Choosing a resistant variety is helpful.

Prevent fruit cracking by maintaining even soil moisture with regular watering and mulching. As is true with most plants, it is better to keep the soil consistently on the dry side (barely moist) than to keep it constantly wet.

Sunscald occurs on green and ripening fruit and appears as a whitish patch on the side facing the sun. This area blisters and becomes sunken with a rough surface. As you may have guessed, sunscald is a problem on tomatoes that are exposed to the direct rays of the sun. It is more of a problem on varieties with less foliage or on varieties that have lost some of their leaves due to diseases, such as blights and leaf spots, or leaf roll. A black mold may also develop on the exposed area, causing rotting thus rendering the fruit inedible.

The solution to sunscald is to cover fruit that is close to the ground with straw or other material or somehow shade fruit located higher on the plant. Grow varieties that produce a dense canopy. Also, control leaf diseases and you will have less sunscald.

Uneven ripening is yet another common tomato fruiting problem. This may be caused by lower than ideal ripening temperatures (below 60 degrees), compacted and wet soil, which inhibits the root system, which in turn, delays nutrient uptake. Low levels of soil potassium also restrict normal fruit growth and maturity.

Unevenly ripened fruits feel hard and may have pits and/or a hard off-color core. Uneven ripening can be identified by yellowish or grayish blotches on the outside of green tomatoes. If you were to cut a slice of such a fruit, you may see the tissue just inside the skin turning a brown color, with pits and cavities. This browning may be the result of the plant being infected with tobacco mosaic virus, or TMV.

Prevent uneven ripening by watering and fertilizing wisely. Water when the soil two inches deep is barely moist and, when watering, apply enough water to wet the soil 18 to 20 inches deep. At planting time, use three to four pounds of 8-8-8 or 10-10-10 or similar fertilizer per 100 square feet of planting area and side-dress every three to four weeks with one to two tablespoons of this same fertilizer per plant. Occasionally giving plants a boost with a fertilizer with high potassium content will help too. Prevent TMV by controlling weeds that may carry the virus and aphids that can transmit the virus. The good news about uneven ripening is that usually only the first or second pickings are affected by it, as later fruit usually ripen normally.

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, former Perry High School horticulture instructor, and former horticulturalist at Henderson Village and Houston Springs. He and his wife, Susan, own and operate Lewis Farms Nursery located on Hwy 26 two miles east of Elko, where he was born and raised. He can be reached at (478) 954-1507 or timlewis1@windstream.net and at LewisFarmsNursery.com.

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