Some of you have commented about seeing small yellow spots on your Pelargonium leaves. This could be Pelargonium rust which is a fungal disease. It travels in the air and is very contagious but with a bit work it is something you can control.
Pelargonium rust only occurs in Zonal Pelargoniums, but that does mean doubles, singles, dwarfs, miniature, and Stella’s are also affected. So, if not recognised and addressed it can become a big problem for your plants.
It first started in Australia and, because they don’t have a proper cold winter over there, it spread unchecked until they were unable to grow Zonals for quite some time until a control was found.
It is most noticeable in high summer. By this time many of the leaves will be covered in brown spots, in the worst cases all the leaves will drop off. When this happens it is best to strip off all the remaining leaves and dispose of them carefully. In fact, cleanliness is the key!
During the rest of the season, up to the winter, keep a lookout for any signs of rust and remove and dispose of them carefully. Bearing in mind it spreads very easily in the air. The winter does bring some respite, so temperature is key in its cycle.
Keeping everything clean and tidy over the winter is good. Then in early spring spraying with an appropriate chemical spray once before they come into flower will help keep it under control.
If you have cured the rust in your garden don’t forget it travels on the wind so it is something you will need to do annually. But as it is only one preventative spray it’s not too bad.
The spray we use is for commercial use only but there are sprays the amateur gardener can use, such as a rose rust, or a carnation rust spray