Leaf spot diseases are typically but not always caused by fungi. Two fungi, Septoria and Alternaria produce leaf spot diseases in multiple crops such as tomatoes, peppers, parsnips, carrots, brassicas, celery and lettuce. Infected plants have brown or black water-soaked spots on the foliage, sometimes with a yellow halo, usually uniform in size. The spots enlarge and will run together under wet conditions. Under dry conditions the spots have a speckled appearance. As spots become more numerous, entire leaves may yellow, wither and drop.