Insect & Disease ID And Diagnosis Guide: Rings, Spots And Dots
Diagnose pest and disease issues that manifest as rings, spots and dots.
January 19, 2009
Seeing rings, spots and dots on your crops? Take a look at these pictures to see common pests and diseases that can lead to rings, spots and dots.
Scouting tip: Consult reference books, Extension literature and notes from grower seminars. Talk with experienced growers, Extension agents and consultants.
Black-rimmed spots on impatiens indicate INSV.
Lupines show leaf spots, drooping of leaves and petiole twisting when infected by an anthracnose fungus.
Irregular brown spots on New Guinea impatiens leaves are caused by the fungus Myrothecium roridum. Look for sporulation on the leaf underside to distinguish from INSV.
White spots with a grainy appearance on poinsettia leaves or bracts indicate powdery mildew.
Round brown spots are a symptom of INSV on cyclamen.
Scattered, 1/8-inch, almost perfectly round spots with a black rim and a paler center are typical for Alternaria leaf spot on impatiens. Yellowing is common.
Scabby spots on sedum leaves indicate powdery mildew. Use a hand lens to confirm.
Whitish haloed spots with a purple rim that buckle out from the leaf, along with lesions along the veins, are signs of poinsettia scab disease.
Tiny, 1/16 - to 1/8-inch, round, brown leaf spots and wedge-shaped areas of chlorosis are symptoms of bacterial blight on geraniums caused by Xanthomonas campestris pv. pelargonii.
Pale yellow spots with diffuse margins seen on the top of a poinsettia leaf signal powdery mildew colonies on the leaf undersurface. Use a hand lens to look for fungus strands on the undersurface.
Pale spots on the upper leaf surface of chrysanthemum may signal the presence of chrysanthemum white rust, which is under federal quarantine.
Tiny yellow dotting across part of a geranium leaf is from aphid feeding.
Zonate spots are a symptom of INSV in coleus. Irregular brown markings may also be seen.
Reddish-brown pustules of geranium rust will start as small bumps, and over time will develop concentric sporulation rings.
Round pale spots on the upper surface of a geranium leaf are signs that brown pustules of geranium rust may be found on the undersurface.
A ringspot pattern may show in TSWV-infected zinnia leaves.