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Ministry of Agriculture, Food and Rural Affairs


Small (0.5-0.5 mm) brown to black lesions on only the upper surface of exposed older leaves with small veins that remain light-coloured or green.  Lesions may coalesce to form spots as large as 2 mm in diameter.  Young leaves are seldom affected.
Often Confused With
Leaf-stippling leafhoppers- both upper and lower surfaces are affected, and nymphs, adults or cast skins are present

Potassium deficiency- both upper and lower surfaces are affected

Period of Activity
Usually most severe after temperature inversion after prolonged periods of warm temperatures and smog conditions in August.

Scouting notes
Some grape varieties, including Concord, Chambourcin and some other French hybrid cultivars, are highly susceptible to injury from ozone.

Early ozone damage Ozone damage Ozone damage Ozone damage Click to enlarge.