Symptom	Plausible Causes	Suggested Treatment
Curled or rolled leaves	Human Causes Air pollution Environment or Disease Leaf scorch Pests Apple aphids, leaf rollers, leaf skeletonizers, psyllids, thrips, weevils
Distorted leaves	Human Causes Irregular water supply Environment or Disease Cold, iron or nitrogen deficiency, leaf scorch. Apple scab, aster yellows, downy mildew, edema, fire blight, mosaic virus, peach leaf curl, powdery mildew, ringspot viruses Pests Aphids, gall midges, gall mites, leafhoppers, mealy bugs, nematodes, psyllids, scale, webworms
Froth on leaves	Pests spittlebugs
Gray or black mold or fungus on leaves	Environment or Disease Downy mildew, gray mold, late blight, peach leaf curl, sooty mold
Small galls on leaves	Environment or Disease Cedar-apple rust, edema Pests Gall mites, psyllids
Small leaves	Human Causes Nitrogen deficiency Environment or Disease Nitrogen deficiency, root rot Pests Nematodes
Sticky leaves	Pests Aphids, leafhoppers, mealy bugs, psyllids, scale, whiteflies
Tan or white bumps on leaves	Pests Scales, in particular oyster shell scale
Watery blisters on leaves	Environment or Disease Anthracnose, bacterial leaf spot, edema, gray mold
Webs on leaves	Pests Leaf rollers, spider mites, spruce budworms, tent caterpillars
White cottony mass on leaves	Pests Mealy bugs
White powder or mold on leaves	Environment or Disease Downy mildew, late blight, powdery mildew
Winding trails in leaves	Pests Vegetable leaf miners, western tentiform leaf miners
Yellow, orange or red blisters on leaves	Environment or Disease Peach leaf curl, rusts Pests Blister mites