Downy mildew in vineyards - Department of Agriculture and Food
Downy mildew in vineyards - Department of Agriculture and Food
Downy mildew in vineyards - Department of Agriculture and Food
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PAGE 6DOWNY MILDEW IN VINEYARDSSymptoms<strong>Downy</strong> <strong>mildew</strong> attacks all green parts <strong>of</strong>the grapev<strong>in</strong>e.LeavesThe symptoms on leaves vary with leafage. On young leaves (i.e. spr<strong>in</strong>g),the disease will appear on the uppersurface as small yellow spots referredto as oilspots; they are about 10 mmdiameter <strong>of</strong>ten with a chocolate halo.These spots tend to grow to about 50mm diameter as they mature <strong>and</strong> thehalo fades. As these spots enlarge theymay appear to cover most <strong>of</strong> the leaf,especially if there is more than one spoton the leaf.<strong>Downy</strong> <strong>mildew</strong> oilspot.Rapidly grow<strong>in</strong>g oilspots <strong>of</strong>ten merge,<strong>in</strong>fect<strong>in</strong>g much <strong>of</strong> the leaf. Often downy<strong>mildew</strong> is not detected until the diseasespreads <strong>and</strong> more oilspots are visible (notethe white areas on the leaves are spraydeposits).<strong>Downy</strong> <strong>mildew</strong> oilspots are <strong>of</strong>ten surroundedby a chocolate halo that fades as theoilspots grow (note the white areas on theleaves are spray deposits).
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