What causes a mosaic pattern on plant leaves?
An irregular patchwork of light and dark green that does not follow the veins is the signature of a plant virus. There is no cure for any of them, so the decision on this page is about containment and about not spreading it further on your own hands and tools.
The one observation that decides it
Rule out the two impostors before you pull the plant. A nutrient deficiency gives a regular pattern that respects the veins, and it appears on many plants at once in the same bed. Herbicide damage twists and narrows the leaf rather than mottling it. A true mosaic is irregular, ignores the veins, usually starts on one plant, and comes with stunting and poor fruit set. Confirm by checking for the vector — aphids or thrips — because that is what will carry it to the rest of the row.
Start from the plant in front of you
8 things it could be
Ordered by how much they can cost you — if the first entry fits what you can see, rule it out before considering the milder ones.
Pale green rings, blotches and vein-banding on leaves in spring, easiest to see on a dull day. Fruit develops sunken rings and brown internal blotches, tastes poor and drops early. Stones of infected plums often show pale rings.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowSeen on: Plums
Yellow mosaic mottling and puckering of young leaves, which often become narrow and strap-like. Plants are stunted, flowers are streaked or malformed, and cucumber fruits are warty, pale and bitter.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowUpward curling and cupping of leaves, yellowing of margins, severe stunting with bushy shortened growth, and heavy flower drop with little or no fruit.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowMottled light and dark green or yellow mosaic patterns on leaves, distortion, puckering and stunting; fruit may be mottled, lumpy or fail to set.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowMottled light and dark green leaves, crinkled and often with dark necrotic streaks down the stems and leaf veins. Plants are noticeably shorter than healthy neighbours and drop their lower leaves early. Tubers may show sunken rings.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowSeen on: Potatoes
Bronzing and inward cupping of young leaves, dark streaks on stems, ringspots and uneven colouring on fruit, and one-sided stunting of the plant.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowSeen on: Peppers
Yellowing between the veins of older lower leaves while the veins stay green, often with reddish or purple tints and curling margins, progressing upward over time.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Fix the cause, not the leafYellowing between the veins of the youngest and middle leaves, with the veins themselves and a band either side staying green — a broader green edging than iron deficiency shows. Beetroot leaves turn red-purple; peas develop the brown "marsh spot" inside the seed.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Fix the cause, not the leaf