Heat Related Tomato Disorders; Yellow Shoulders and White Cores
If your tomato harvest wasn’t up to par this season, you can blame it on the weather. High temperatures can prevent fruit set, delay ripening and impact fruit quality.
When temperatures soar to above 90 during the day and stay above 70 at night, tomato plants suffer producing fewer flowers and setting less fruit.
Even after the fruit is set high temperatures can slow ripening. Tomatoes ripen most quickly when the temperatures are between 68 and 77 degrees.
High temperatures also cause fruit with yellow shoulders and white cores. Excessive heat prevents the production of lycopene, the red pigment in tomatoes resulting in yellow shoulders.
We can’t change the weather, but maintaining ample foliage on the plants, providing ample moisture and fertilizing properly will help reduce the risk of these disorders.
A bit more information: Harvest yellow shouldered tomatoes when the bottom portion is ripe. Cut off the tougher yellow portion and toss it in the compost pile. Do the same with those with white cores. Cut out the white tasteless portion and use the rest. Missouri Botanical Gardens has more information on tomato diseases and hot weather related problems. A tough white core in the center of the fruit may also occur under these stressful conditions.