Around the spots, the tissue may become yellow.

The first sign is small, brown lesions on aged foliage. The fungus Alternaria linariae causes early blight. The first symptoms include yellow or pale green spots on the upper leaves, turning yellow and, under especially humid conditions, covered with gray, velvety spore growth. Leaf mold affects older leaves near the ground where the air may not circulate as well and humidity levels are high.

Look for brown to black round spots that are the size of a pencil tip or larger that leads to yellowing.īacterial spot forms small, irregularly shaped spots with a yellow outer ring and dried-out centers that tear on the leaves and can affect green tomatoes with slightly raised spots on the tomatoes themselves. The infection begins on the bottom leaves and can spread upward if not treated early. Septoria leaf spot rarely affects the fruit. Most thrive in areas with high summer humidity. Most tomato leaf diseases overwinter in the soil and then splash onto the lower leaves of the plant during watering. Fortunately, they are all treated using the same methods. In the early stages, it is nearly impossible to distinguish between leaf spot, leaf mold, or early blight.

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