Rust fungus on geraniums becomes particularly common in hot, humid weather. The disease appears as brown pustules on the reverse of the leaf. The upper surface becomes blotchy and yellow, eventually dying. The disease is quite debilitating on plants and reduces vigour and the plant's ability to produce flowers.
Control
Chemical: Pick off affected leaves.Spray with Mancozeb Plus or Baycor, mainly onto the reverse of leaves.
Cultural: Prune stems by 60% and remove all diseased leaves on the plant, on the soil surface and in the pot. these should be discarded not placed in compost. Fertilise with Garden Gold or Blood & Bone every 3 months to encourage healthy new foliage. Once new plant material produced, feed with Better Bloom to encourage more flowers. Pick off any diseased leaves as they appear.
NB Ivy leafed geraniums appear to be more resistant to rust disease.
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