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Problem-specific reference photo
under review

Problem-specific reference photo under review

Fungal & Oomycete · Plant health field guide

Downy mildew

Downy mildew-like diseases often produce upper-surface discoloration and growth below the leaf.

Act soonPossible cause—not a diagnosis. Compare the visible signs, plant identity, and growing conditions before treating.

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Signs you may notice

angular yellow patches
downy growth below leaves
rapid spotting

Safe first checks

Compare top and underside patterns and seek expert confirmation before treatment.
Separate the plant if the problem may spread.
Remove only badly affected material with clean tools.
Improve airflow and keep affected foliage dry while you compare the signs.

Can look similar to

Overlapping symptoms are common. Compare these alternatives before choosing a treatment.

bacterial leaf spot
powdery mildew
edema

What to avoid

Do not assume every spot is infectious or use a disease-specific product without confirming the host and pattern.

Record and follow up

Photograph the same area in consistent light and note whether lesions enlarge, appear on new leaves, or stop after conditions improve.

Seek qualified local help when damage is severe, rapidly spreading, or may involve a regulated pest or disease.