Here is a quick guide to pests and diseases that Rhododendrons can be prone to.
Symptoms: Clusters of insects on young growth
Remedy: Spray with Mavrik or Confidor at 2 weekly intervals
Symptoms: Leaves yellow (stippled or mottled) and dehydrated in hot dry weather
Remedy: Spray with mite killer
Symptoms: Leaves silver and dry. Brown-black specks appear on underside of leaves
Remedy: Spray with Mavrik or Confidor at 2-3 weekly intervals through summer
Symptoms: Black sooty mould on leaves and twigs
Remedy: Spray with Mavrik or Confidor
Symptoms: Earliest symptom is light brown or whitish coloured circular spots on petals. Spots enlarge to form irregular blotches until whole flower collapses. Petals feel slimy when rubbed between fingers. Diseased flowers dry up and cling to the plant (leaves and stems are not affected).
Remedy: Avoid overhead watering. Pick off diseased flowers. Spray at two weekly intervals with GroSafe Fungus Fighter.
Lack of fertiliser
Symptoms: Leaves yellow and/or develop dark purple tone. Slow, stunted growth
Remedy: Fertilise with Butlers Azalea, Camellia and Rhododendron food in late spring after flower finishes and just before new growth starts
Soil too alkaline
Symptoms: Decline in vigour and leaves turn yellow while the veins remain green
Remedy: Fertilise with Butlers Azalea, Camellia and Rhododendron Food in late spring after flowering finishes and just before new growth starts. Do NOT lime.