Blights

Leaves, flowers, stems, and branches that suddenly wilt, wither, and die are common indications of blight. Common garden blights include Botrytis, early/late blight (caused by fungi), and fire blight (produced by bacteria).

Cankers

Affected woody plants produce dead, and often sunken, patches in stems and branches. These cankers may ooze a sticky and/or foul-smelling material that can spread to kill whole trunks or shoots. The fungal Cytospora canker is a common orchard problem; bacterial fire blight is another canker-causer.

Galls

Swellings or overgrown patches of leaf or stem tissue are known as galls. They can be caused by fungi (such as leaf gall), bacteria (crown gall) or even insects (such as gall wasps).

Leaf Curl

Deformed and/or discolored leaves suffer from leaf curl. Peach leaf curl is caused by a fungus, however viruses may also produce these symptoms.

Leaf Spots

Rounded or irregular areas in various colors are common leaf symptoms. They are produced by a large array of pathogens.

Mildews

Dusty white, grey, or purplish patches on the surfaces or undersides of leaves are an easy clue to the fungal powdery and downy mildews.

Rots

Soft or discolored and dying plant tissue generally indicate some kind of rot. Fungi and bacteria are possible causes of rot on fruit, stems, flowers, or roots.

Rusts

Orange or yellowish spots, galls, or coatings are caused by rust fungi. Rusts may affects leaves, stems, flowers, or fruits.

Wilts

Drooping leaves and stems indicate that the plant isn't getting enough water. This can be caused by improper watering or by fungi and bacteria that can clog the plant's water conducting system. Fungi cause Fusarium and Verticillum wilt; bacterial wilt is a problem in cucumbers and related crops.