The potatoes have been beautiful as well as delicious this year. You can understand my surprise and disappoint when I harvested some the other day that were less than beautiful. They had a common potato disease called potato scab.
Still OK to Eat
The good news is they’re ok to eat and still delicious. Just cut the unsightly part away from the skin and/or flesh and cook as you normally would.
Common potato scab occurs throughout the potato growing areas of the world. It doesn’t affect yields and isn’t harmful to us, but none of us want our potatoes to look like that.
Common Scab and Your Organic Garden
The severity of common scab is said to be significantly reduced in soils with ph levels of 5.2 and below. But if you have an organic garden to which you consistently add organic material over the years— your soil will probably be about like mine with a ph of 6.5 to 6.7. Potatoes won’t find an acid soil in our gardens.
That’s what organic material turning into organic matter does to soil. (And I include pine tags, oak leaves and the like which are said to be acid.)
Interesting that 6.5 ph is almost the perfect ph to allow vegetable plants to take up the nutrients they need. And your yields will be much higher — even with potatoes. Acid soils are just not favorable to most vegetables.
I’ve grown potatoes in my organic garden for about 30 years and have had the scab disease in maybe 3 to 5 of those years.
There are no above ground symptoms so you won’t know you have it until you dig your potatoes.
The disease can appear in several forms pictured below:
How Do You Get It in Your Soil?
The pathogen that causes the disease can occur naturally in the soil. But commonly it is introduced by seed potatoes that have the disease. (Important reason to get certified free from disease seed potatoes.)
Things You Can Do to Cut Down on the Chances of Having It.
1. Seed potatoes that are not certified free from disease could have the pathogen that causes scab disease even though they show no visible signs. Plant only seed potatoes that are certified disease free.
2. Some varieties of potatoes although not totally immune to the disease are more resistant to common scab disease than others. When you can, buy the resistant varieties.
3. Heavy mulching will help maintain soil moisture. This is especially important during the first 2 to 6 weeks after the green leaves emerge from the soil. Potatoes that have to bulk up without adequate moisture are more at risk to the pathogen that causes the disease. Scab can be more severe when tubers develop under warm, dry soil conditions.
4. Follow a crop rotation schedule.
- Follow potatoes for at least 3 years by crops that are not susceptible to scab. (Many root crops like radishes, beets, turnips, and carrots can be infected as well as potatoes.)
- Corn, alfalfa, rye or soy beans planted in soil after potatoes with scab are said to be especially able to “starve out” the infestation.
- Rotation does not totally destroy the pathogen, but eventually reduces it.
5. Avoid using manure to fertilize potato beds. Because it’s alkaline it can cause an increase in the microorganism that causes scab infection. (Use composted manure the fall prior to planting.)
6. Avoid red clover as a cover crop where you eventually plan to plant potatoes. It stimulates the pathogen. Never use red clover in beds where you’ve already had a problem with scab.
7. Keep in Mind:
- This pathogen can survive passage through an animals digestive tract and be distributed when the manure is used.
- Avoid digging the peels from the diseased potatoes back into your soil.
- It would be wise to stay away from composting them as well, unless you know your compost gets hot enough to kill the pathogens.
Not everything in your garden is going to be perfect all the time. But if you follow the practical advice given above, over time you’ll find the looks of your potatoes greatly improved. In the meantime, cut off the part that’s disfigured and enjoy the rest.
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Great tips. Timely too, because I’m planning a bed to grow potatoes next year. Also, very good thing to keep in mind about perfection and lack thereof. Just enjoy what you get.
Thank you for the great tips about how to prevent scab. Greatly appreciate it. I have grown organic red potatoes that originally sprouted 4 years ago. The planting area changed each year as we moved to different homes. We moved shortly after harvest time last year and I again saved some of the smaller potatoes to grow. The area I chose is in nearly full sun had been fertilized by sheep for several years and had a great deal of pumice in it as well. I planted as usual and dug some up today and disappointingly they are scabby.
I have told you all this to ask this question: Are the seeds from these potatoes okay to try to grow or should I destroy the little seed balls? They never put out seeds from the flowers before this year.
On July 24, 2013 in the comments sections of the post https://tendingmygarden.com/growing-potatoes-planting-in-best-and-worse-conditions/ I placed the following comment in answer to a readers question like yours:
Real potato seed from the top fruit (resembling a small tomato) that potatoes can develop (this is sexual propagation by the way) — will develop into a plant with unique characteristics — not necessarily those of the potato from which it came. Each fruit can contain 300 seeds — theoretically you could get 300 plants — all different from each other and different from the the parent plant.
Real potato seed is used in breeding programs.
Two great things about growing from the real seed of the fruit produced by the potato is that genetic diversity will be high and the seeds don’t often carry diseases.(It’s my understanding there are very few seed-borne potato diseases.)
If you have the time and are so inclined — you could eventually come up with potatoes that thrive in your unique conditions. There’s a good chance that the plants will be less susceptible to the pests and diseases than the ones you now plant from tubers (seed potatoes). When you finally come up with the potato you consider a winner — you would then reproduce the potatoes from tubers (as you already know).
I think if I were younger and just starting to garden — I would be very interested in doing this. But – as I said — it takes a lot of time and — I would think — record keeping. It can get quite complicated and if you’re going to do it — do as much research as you can to find all the little secrets that will save you time and effort and keep you from unnecessary mistakes. (As always with any research — be careful who you believe.)
Also, I think that the first year only produces mini-sized tubers — not full sized potatoes. So in order to really know what you’re going to get — you have to save the mini-potatoes over until next year and plant — as you have already mentioned. With that second year harvest — you should know what the results are.
After that, to make sure you get the same kind of potato as the new plant you started with — you must grow potatoes from “seed potatoes” (this is vegetative propagation)— the potatoes already produced by your new parent plant. This is also called cloning. It assures genetic purity and also favors high yields.
Last year my little garden produced 3 bushels of ‘Adirondack Red’ potatoes from about 5 lbs. of seed potatoes, and most of them were above average in size, much larger than a big man’s fist. It was delightful to dig, and ‘season’ them, and they were easy peelers. The space used was 12′ x 12′ with much gravel !
I heard good things about a potato called German Butterball and tried it, for I wasn’t very fond of purple mashed potatoes….the ‘red’ of the Adirondacks is all the way through, but it was very tasty.
This year’s yield was horribly disappointing, with egg or marble sized, potatoes and very few of them, not enough to fill a brown paper bag! I have NO idea why…… We did use some dried horse manure fertilizer.
(unless the sun was too hot for them.)
Please help ! Hopefully, Carol
Carol, all you’ve basically told me is that the potatoes you planted this year didn’t do well.
That’s not anywhere near enough information to even make an educated guess at what your problem might be.
Here are a few general comments to point you in your search of the cause.
1. Different varieties will do better for some gardeners than others.
2. Hopefully you rotate your placement of nightshades (peppers, potatoes, tomatoes, eggplants) and don’t plant the same spot with those each year. (There are exceptions, but no time to go into that now.)
3. Are you building your soil with the addition of organic material every year?
4. I assume that your horse manure had no residual herbicides in it.
Your might want to search my site for all posts on potatoes and read those. Then you might want to search and read the posts on residual herbicides.