April 19th, 2011 by Marc Opperman
I robbed a couple potatoes from my still-growing forest of potato plants. I hand-dug below a red pontiac plant and a kennebec plant, and came up with a pair of pretty tubers. Both of these would be considered “new potatoes” since they are the earliest from the crop.
The small one was from a smaller plant I pulled a few days ago. The larger red pontiac’s skin is torn from me trying to wrest it from the ground. Maybe I need to cut my fingernails.
That’s the good news. The bad news is that the red pontiac had a couple sizable scab lesions.
Potato scab is lesions on potatoes caused by the presence of a bacterium in the soil, Streptomyces scabies. It causes various forms of lesion, either pits or raised welts, seemingly dependent on the growing conditions and variety of potato. It isn’t harmful to humans, but it does render the otherwise pretty potato unsightly. In extreme cases the lesions take on a corky, pithy form that is unappealing to eat.
I knew my soil conditions might be right for scab when I planted the seed potato slips, but I had done some work to try and condition my alkaline soil to help ward off the pathogen. The bacteria doesn’t do well in soils with a pH below 5.2, so boosting the acidity of the soil with compost is something growers often do. (Compost can raise soil acidity). However, I’ve seen warnings that using manure-based composts might aggravate the condition. I used Natural Gardener turkey compost to help acidify my soil some.
For next year I may have my soil tested professionally and amend it accordingly with something more like coffee grounds or another acidic agent that doesn’t contain manure compost. Another factor seems to be to maintain consistently-high soil moisture. This allows other non-harmful soil bacteria to out-compete s. scabies.
Whatever the case, my two potatoes will be breakfast tomorrow. The scab on the red pontiac is easily cut off. I plan to enjoy thinly-sliced potatoes sautéed in olive oil with minced garlic and maybe a bit of chopped garden onion.