Hydrangea pests and diseases: how to recognise them

At a glance

How to grow hydrangea · All pests and diseases

Pests

• Scale insectsSmall round or oval bumps on stems and along leaf veins, mostly underneath, that do not move and look like shells or scabs.Photo: BARAKAT2011, CC BY-SA 3.0, Wikimedia Commons
• Vine weevilDull black, pear-shaped weevils about 9 mm long with dirty-yellow flecks, feeding at night; they cannot fly.Also called: black vine weevilPhoto: Opuntia, CC BY-SA 3.0, Wikimedia Commons

Diseases

• Grey mouldFuzzy grey-brown mould on decaying buds, flowers, leaves, stems or fruit in humid weather.Photo: Schlaghecken Josef, CC BY 4.0, Wikimedia Commons
• Cercospora leaf spotMany small, round spots with a pale brown to off-white centre and a red to reddish-purple margin.Photo: Plant pests and diseases, CC0, Wikimedia Commons

Which hydrangea problems need quick action?

These spread or do lasting harm fast; check the plants and start treatment the day you see them.

• Grey mould: Small, almost translucent spots that turn brown and water-soaked; affected tissue goes soft, dark and dies, and buds and flowers shrivel.

Plants with many of the same problems

• African violet (3)
• Tuberous Begonia (3)
• Cyclamen (3)
• Gloxinia (3)
• Grape (3)
• Geranium (3)
• Rhododendron (3)
• Blackberry (2)

Which plants each problem affects: sources

The links between these problems and the plant were checked against these pages.

1. extension.umd.edu/resource/scale-insects-indoor-plants
2. ipm.ucanr.edu/PMG/PESTNOTES/pn7408.html
3. rhs.org.uk/biodiversity/vine-weevil
4. ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/blvinwee.html
5. rhs.org.uk/disease/grey-mould
6. ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/botrytis.html
7. hgic.clemson.edu/factsheet/hydrangea-care-in-south-carolina/