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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