Geranium Rust.

Latest Update 16th December 2014.

Geranium Rust.
  • Binomial Name:                                               Puccinia pelargonii-zonalis.
  • Family:                                                           Pucciniaceae.
Notes. 
  • Geranium Rust is fungus that grows on living plants and plant debris.  Movement of infected plant tissue can spread this fungus, and infection occurs readily if leaves are wet for 5 or 6 hours at 13°C to 24°C.  Spores could remain infectious for at least 3 months.
  • Considerable genetic variation exists between cultivars, and immunity varies considerably.  
  • Both leaf surfaces first develop white or yellowish spots and those on the lower surface enlarge and look like blisters (see photo). These brown powdery markings are evident on leaves and sometimes on stems.
Why Geranium Rust is a Pest.
  • Severe leaf infection causes total yellowing and defoliation.  Eventually the plant will die.
Organic Pest Control.
  • Avoid wetting the plant's foliage.
  • Reduce humidity by spacing plants wide enough apart to provide good air circulation.
  • Inspect all plants regularly for signs of the disease, including new ones. Destroy diseased leaves and severely affected plants.  Do not recycle them unless you are confident the fungi will be killed in the process (e.g. hot composting).
  • Fungal plant pathogens like Puccinia pelargonii-zonalis are vulnerable to microbial predators in the soil.  For this reason it is important to maintain an active community of micro-organisms in the soil by adding plenty of homemade compost before planting your Geranium.
  • There are also communities of beneficial microbes living on the surface of the Geraniums leaves, and the activity of these can be boosted by applying a foliar spray of aerated compost tea regularly.