Plant Disease Symptoms and Causes What you see Leaves mottled or discolored Possible Causes Mosaic; nutrient deficiency, ozone, or sulfur dioxide injury; sooty mold; sunscald; yellows; insect pests What you see Leaves with yellow or brown spots Possible Causes Anthracnose; apple scab; bacterial spot; Botrytis blight; cedar-apple rust; downy mildew; Septoria leaf spot What you see Leaves curled, cupped, or blistered Possible Causes Bacterial spot; black spot; cherry leaf spot; late blight What you see Leaves, shoots, or fruit with white spots or patches Possible Causes Downy mildew; powdery mildew; salt injury What you see Leaves and stems wilted and dying Possible Causes Bacterial wilt; Dutch elm disease; Fusarium wilt; oak wilt; Verticilium wilt; waterlogged soil; lack of water What you see Leaves or stems with orange spots Possible Causes Rust What you see Stems with irregular swellings Possible Causes Black knot; cedar-apple rust; crown gall What you see Stems with oozing slimy or gummy substance Possible Causes Cytospora canker; slime flux What you see Stems condensed into short, bushy "rosettes," plant stunted Possible Causes Peach rosette; nematodes What you see Stems of seedlings rotted at the soil line; infected seedlings collapsed Possible Causes Damping-off What you see Flowers or fruit with brown spots Possible Causes Brown rot; Botrytis blight or fruit rot; fire blight; frost damage What you see Fruit with small, dark sunken spots Possible Causes Anthracnose What you see Apple fruit with green or velvety brown spots that turn into raised, dark, corky areas Possible Causes Apple scab What you see Fruit with water-soaked spots that turn brown and leathery at the blossom end Possible Causes Blossom end rot What you see Roots of young and old plants rotted; plants stuntedor wilted Possible Causes Root rot What you see Roots with irregular swellings Possible Causes Club root; crown gall; nematodes