This is pictures of a Brandwine Pink & Reds. There is something that is causing the discoloration but we aren't sure what it is. Could it be iron chlorosis? I am organic and have used Serenade Fungicide on them but will use Copper if needed. Sometimes the color will return to green and mostly the discoloration is on the lower leaves. A few cooler nights will cause it is get yellow as well. What is happening and what can I do?
Hi- this appears to be a symptom of some minor environmental stress. Older leaves naturally turn yellow and die with age. It's possible there is a nutrient issue but this does not appear to be iron chlorosis.
We actually recommend removing the lower 3-4 leaf branches on well-established tomato plants that are beginning to form fruit. This helps improve air circulation leading to more rapid leaf drying and slower spread upwards of foliar diseases. You may also want to monitor leaf undersides for any signs of spider mites although your photos do not suggest mite feeding.
Liquid copper could be applied during the season if fungal leaf spots (early blight and Septoria leaf spot) become prevalent. Follow label directions closely and don't spray any pesticides during hot weather.