Early blight, the most common fungal disease of tomato. It causes lower leaves to turn yellow then brown. On closer examination you’ll see brown spots with concentric rings of dead tissue. Later, tomato fruit will develop rotten spots. Staking plants to improve air circulation and quick drying is an important control measure. Fungicides work very well but most gardeners are not interested in spraying plants and despite the infection, plants usually produce a decent crop… for a few weeks. The fungicide chlorothalonil is effective in preventing the disease spread and is available over the counter in garden centers. Organic gardeners can use copper fungicides and get limited control.
My strategy: 1) Stake ‘em up early and often 2) have a second planting coming on and abandon the first when the disease overwhelms them in late August. Go ahead and compost that old stuff.
Blossom end rot causes a dry, leathery, brown rot on the blossom end (opposite the stem end) of fruit. Caused by calcium deficiency. Hard to fix now. Soil test and add needed calcium with lime or gypsum in the fall to boost Ca levels for next year. A Penn State Soil test will tell you how much. Sometimes blossom end rot shows up in gardens with adequate calcium. Anything that prevents the plant from absorbing calcium from the soil, such as moisture extremes or root damage can result in blossom end rot. Sometimes plants have affected fruit for a while and then snap out of it.
Viral diseases mimic herbicide injury. Saw several cases last week. My guess is cucumber mosaic virus but that is just an educated guess. Viral diseases cause weird plant distortion and mottled, mosaic patterns (several shades of color) on fol age and fruit. Fruit are often undersized and misshapen. Viral diseases are a tough case because there is no cure. The virus lives in other plants, often hundreds of species, including ornamentals and weeds and is transmitted by insects such as aphids and leaf hoppers. They can even be transmitted by human handling of infected plants. You may see viral symptoms on beans and vine crops also. I do not know why virus diseases are devastating one year and almost non-existent in another. This is looking like a good year for viral diseases.