Are Silver-Grey Spots on Potatoes Harmful?

For some time now, I have noticed that the skin of organic potatoes has white and grey-brown spots. This is the case with almost all potatoes, especially with the Ditta variety. What are these spots and can you still eat the potato?

With something like this, I always wonder if I should stick with organic and put up with those stains, or should I go with non-organic and get potatoes that look good and don’t rot or get moldy.

The spots are probably a fungal disease. The fungus  Helminthosporium solani  triggers the so-called silver scab. In terms of health, this is completely harmless for us humans.

However, affected tubers have poorer skin quality, which can lead to water and weight loss.

The pathogen penetrates the cork layer of the tuber skin and detaches it from the cell tissue. The resulting small gap fills with air, which leads to the formation of the shell’s silvery sheen. With red or blue-skinned tubers, the spots are particularly easy to recognize due to the destruction of the pigment deposits. The spots are sharply defined and have a brownish edge. (Similar spots with brown to dark gray spots and an irregular and blurred border are caused by another fungus, the  Colletotrichum coccodes, the infestation leads to the so-called wilt disease.)

Immediately after harvesting, the spots are usually very small. In storage, under suitable conditions, the fungus can spread well and cover a considerable part of the tuber surface.

Washed tubers are more susceptible to silver scab, as micro-injuries can occur during washing. However, tubers that have already been infected can also be identified more easily after washing.

Direct control is currently not possible in organic farming. However, since the fungus has a negative effect on the appearance of the potatoes and is harmless to humans, we believe that you can continue to use organic products, even if they do not always look great or can be stored for as long as conventional products.

Organic or non-organic is an individual decision of each individual. For example, no artificial fertilizers or synthetic pesticides may be used on organically grown potatoes.