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Diseases and pests

Rhododendron 'Rosy Lights'.
Photo: Jardin botanique de Montréal (Gilles Murray)
Rhododendron 'Rosy Lights'

Black vine weevil
(Ostiorhynchus sulcatus)


  • Leaf edges damaged by adult weevils
  • Roots attacked by larvae
  • Plant partially or totally wilted

Control methods:

  • Do not overwater.
  • Inspect plants starting in mid-June, after sunset (when the adults are active).
  • Pick off and destroy any weevils.
  • Place sticky strips around the base of the main stems.
  • Use nematodes to control larvae in the soil.

Root and crown rot
(Phytophtora sp.)


The fungus lives in the soil, proliferates in stagnant water and gets into a plant through a damaged crown or roots.

  • Plant partially or totally wilted
  • Stems, petioles and leaves turn brown

Control methods:

  • Mulch the soil and avoid damaging the roots.
  • Do not overwater.
  • Remove plant debris.
  • Destroy any severely affected plants.

Powdery mildew
(Mycosphaerella sp.)


  • Powdery white down on upper and sometimes lower leaf surfaces

Control methods:

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