Geranium Rust & Pests
Answered by: Conrad Richter
Question from: Arthur Philip
Posted on: April 30, 2006

Thanx for making this facility available.

I am the franchise holder for a company called Talborne Organics in KZN. During a visit to one of my Rose Geranium growers I noticed there was a type of rust infection. I have taken some photos of which one is attached. On closer investigation I noticed some little white insects. I believe it was "white fly" but I am not sure. With some difficulty, I managed to get a picture of this little creature. (photo attached) unfortunately, I was only able to capture a photo of an immature insect, as all the mature ones would not allow me to get close enough to get a shot. I am hoping you will be able to shed some light on the rust type, and maybe identify the insect.

The immature insect does not appear to be whitefly. But it is difficult to be sure because there are many species of whitefly and we are only familiar with the greenhouse whitefly (Trialeurodes vaporariorum) and the silverleaf whitefly (Bemisia argentifolii) common in North American greenhouses. Trying to identify insects at non-adult stages is also very difficult, especially from a photograph.

Whiteflies are common pests of scented geraniums so it is quite likely that they are what your grower has. It may help you to feel more confident of your identification by comparing the adult flies with photos available on the Internet. Here is a link to many whitefly images using Google:

Google Whitefly Images

The "rust disease" shown in your photo does not look like a typical geranium rust disease to us. We do not believe that it is a biotic disease (i.e. one caused by a living organism such as bacterium, virus, or insect). Instead we suspect that it is a sign of stress, perhaps from drought or nutritional deficiency. Typical geranium rust disease caused by a fungus causes yellow spots on the upper surfaces of the leaves and rust-coloured spots on the lower surfaces. On closer examination the rust colour appears when rust coloured spores develop as the fungus reaches the fruiting stage. If you rub the leaves during this stage, the rust should smear. If, however, the colouration is caused by environmental stresses, the colouration will not smear when rubbed.

It is important to get a definitive identification of any disease or pest problem plaguing your crop. The only way is to send samples to a competent plant disease disgnostic lab. In most developed countries diagnostic lab services are available at commercial, government or university institutions.

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