Hi everyone! I'm hoping that someone knows what is wrong with my potatoes. This is my 2nd year growing them and I did choose to grow them in the same place as last year. The problem is that a lot of them have brown scab looking like things or brown pock marks on them. (OK, I realize this sounds strange, but I am a real person and this is a real question.) Most of my potatoes are Yukon Gold, with some red, a few russet of an odd variety, and a few purple. None of the russet are affected, but as I said, they are an odd type that seems to have a thick smoothly scaly skin. All the others are affected in an equal percentage. All the affected ones are the thin skinned types, am I right that this has something to do with it? (I am guessing that this is some very common thing, and I will feel a bit like an idiot, but, hey, if I'm not brave enough to look foolish I guess I'll have a hard time being me as I do that all the time! Ha, ha! Extra question: Can I eat the potatoes? (Please say yes...) Thank you all in advance for your time and trouble, Leslie (real e-mail address ho

-- Leslie in Oregon (leslie@cntdu2trlls.com), November 29, 2001

Answers

Hi Leslie,

Potato Scab is a fairly common gardening problem. If you go to Google and type in Potato Scab, you'll get several sites that discuss the problem and what to do about it. From what I've read, there doesn't appear to be a problem eating the potatoes, because the scab comes off when the potatoes are peeled. Don't know about baking them.

I copied the information from the U of Vermont and have pasted it below for you.

Hope this helps.

University of Vermont Extension GD 7

Potato Scab

by Alan Gotlieb, Extension Plant Pathologist and Ann Hazelrigg, Plant Diagnostic Clinic Coordinator, Plant and Soil Science Department

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Symptoms

Shallow surface scab consists of a superficial roughened area often raised slightly above or sunken slightly below the plane of healthy skin. Scab lesions vary in size and shape and usually are slightly darker in color than normal skin. Pitted or deep scab lesions can be up to 1/4 inch deep and are often darker than shallow lesions. Scab infections occur on young, rapidly expanding tubers as well as on stems and roots of potato plants. Tubers infected with scab are often attacked by chewing insects and invaded by rotting organisms. When scab lesions are deeply pitted, there is a lot of peeling waste.

Cause

Scab is caused by the bacteria-like organism Streptomyces scabies. The organism can survive indefinitely in slightly alkaline soil but is relatively scarce in highly acid soils. This is why addition of alkaline-producing materials such as lime, ashes, and manure to a garden having acid soil may suddenly increase scab occurence. The organism can be present in soil where potato has not been previously grown. It is distributed by infected seed tubers, in wind and soil, and in fresh manure since it can survive the digestive tract of animals.

The organism enters through pores (lenticels) in stems, through wounds, and directly through the skin of young expanding tubers. In addition to potato, other susceptible crops include beets, radish, turnip, carrot, rutabaga, and parsnips. This should be kept in mind when planning crop rotations.

Control

Control in the vegetable garden for the most part involves correcting the conditions that are favorable for scab production.

Cultural

Soil pH and fertilizer choice

Keeping the soil pH at or below 5.2 will suppress scab. You can apply sulfur to the soil to lower the pH and make it more acidic. See your local Extension office to get your soil tested to determine the amount to apply. In addition, acid-forming nitrogen fertilizer, such as ammonium sulfate and diammonium phosphate, is more effective in reducing scab than ammonium nitrate is, while calcium and potassium nitrate can raise soil pH which may favor scab development. Fresh barnyard manure applied to the soil can create a scab problem and the pathogen may persist in the soil for many years afterward.

Crop rotation

Follow a rotation schedule when scab is a problem. Plant at least three years of nonsusceptible crops between potato crops. Scab infection builds up following frequent crops of potatoes, beets, radishes, turnips, carrots, rutabagas, and parsnips. Rotations that include rye, alfalfa, or soybeans may reduce scab severity. Keeping soil moist during early tuber development may help control scab. Do this for about 2 weeks after the plants emerge from the soil. Avoid overwatering because it may cause rotting or poor plant growth.

Varietal Resistance

Plant certified seed potatoes of the russet-skinned varieties, since they have more resistance to the disease. The variety Nooksack is highly resistant, while Russet Burbank, Netted Gem, and Norgold have moderate resistance. A red variety, Red Norland is also moderately resistant.

Resistant Alamo, Catoosa, Early Gem, Haig, Hi-Plains, Norgold Russet, Ona

Moderately Resistant

Belleisle, Belchip, Norchip, Norgold, Norland, Plymouth,Russet Burbank, Russet Sebago

Slightly Resistant

LaRouge, Sebago, Viking Fungicide Seed Treatment

In situations where growers are planting in ground not planted previously with potatoes or where the field is known to be scab-free, treat seed tubers with a fungicide seed treatment to reduce scab introduction through the seed pieces.

-- Ed (ecupubs@lynchburg.net), November 29, 2001.

Ed, Thank-you SO much. I heavily mulched that area for 2 years with horse manure and I guess I caused my own problem, or exacerbated it. Guess I'll try to bring the acidity of the soil up, (in some 'natural' way; I'll have to look into the sulpher idea...) and plant soy beans there this year. In my area of Oregon, in the fir forest, soils tend to be acid but I guess 1 1/2 foot of manure is a bit overdoing it. Thank-you so much for your patient and thorough answer. :) Leslie

-- Leslie Coray (leslie@webolium.com), November 29, 2001.

Leslie...

Don't guess .... soil test It is easy and will tell you much information.If you need more help contact your local extension office and ask for a "Master Gardener". They will be glad to help with many garden questions. I am an Ohio "Master Gardener".Have fun and Good Luck

-- Ralph in N.E.Ohio (Roadapple@suite224.net), November 29, 2001.

Leslie, we're north of you in bc and potatoe scab is very normal with us as we're trying to build up poor, forest floor soil. We don't really worry about the scab, It comes off when you peel the potatoes. If you bant to bake , simply cut off the scabs, wash and bake as normal. Easier than trying to get rid of it. How's the snow down your way. We got the blizzard , just stopped snowing this afternoon. Temp dropping like a rock, 23 below and still falling. Guess we've got winter! Good luck. Tomas

-- tomas (bakerzee@hotmail.com), November 29, 2001.

Ralph, Thank-you so much. I think that the U of O has an extension office... I'll check this out. :) Tomas, Does the fact that the disease has both Strep. (a virilent bacterium,) and Scabies, (a virilent parasite,) not worry you a little as far as eating the potatoes??? No, seriously, I've already eaten some, and I didn't die, yet. Of COURSE I tried eating them. Hey, this is Oregon, where women are tough and men are..... Sorry, I'll behave. Our weather here has been awesome for Nov. It WAS just starting to get below freezing at night, but began raining and the temp. went up. The weather people were saying we were going to have solid rain for 5 or 6 days, very heavy, which in Oregon means that you had better sleep in your neighbors boat, (on account of; its bigger than your own boat,) but actually it has only rained a little today and we had some, (please don't hate me,) SUN. I hope that you are warm and toasty and enjoying the indoors. If you want any good Native American beadwork patterns I'll send you some. :)

-- Leslie Coray (leslie@webolium.com), November 29, 2001.