Insect & Disease ID And Diagnosis Guide: Discoloration

Broad mite feeding causes bronzing on the underside of begonia leaves.

An overdose of a systemic insecticide caused this phytotoxic response in poinsettia leaf tissue.

Brown blotches and leaf drop can signal downy mildew on coleus.

Fringed, purplish-brown to black, 1⁄4-inch spots appear in an established Cercospora leaf spot infestation on pansy. Examine older leaves to find the most characteristic symptoms.

Yellow lines perpendicular to veins may show in hosta leaves infected with HVX.

Blackened veins in this impatiens are not the result of virus infection, but are the response to root uptake of a dilute chlorine bleach solution.

Major element deficiencies of nitrogen and phosphorus may result in reddening or yellowing of portions of geranium leaves.

Tiny, rust-colored flecks and yellowing on geranium leaves beginning at leaf margins are symptomatic of iron or manganese toxicity, resulting from growing at a pH of 5.8 or below on sensitive cultivars.

Faint yellow stippling similar to mite injury signals downy mildew on impatiens — turn leaves over to see white sporulation.

Powdery mildew can cause discolored patches on petals of gerbera.

Lower foliage yellowing on pothos signals the likelihood of Pythium root rot.

Ficus leaves infested with eriophyid mites may discolor and drop from the plant.

Scorched dead areas along the outer edges of poinsettia leaves may indicate excessive levels of sodium or boron at the margin or, in some cases, zinc deficiency.

Pronounced scorching of leaf edges on this mum resulted from an accidental overdose of a slow-release fertilizer.

Yellow mottling is typical of INSV on begonia leaves.

Whitened bracts or stem tissue on poinsettia may result from large Bemisia tabaci - B Biotype whitefly populations feeding on the plants.

Light-colored, serpentine mines through gerbera leaves signal leaf miner feeding. Look for miner frass, pupae, or larvae in the tunnels.

Browning at the base of these New Guinea impatiens leaves is caused by Rhizoctonia attacking tissue in contact with the rooting mix surface.

Feeding by four-lined plant bug can resemble a fungal or bacterial leafspot.

Angular, brown leaf spots on rudbeckia are caused by the fungus Septoria sp.