Potato Scab!

[Susan BBPM]

I'm fairly new to gardening and still at the stage of "stick it in the ground, water it and be totally gobsmacked when it works!". Equally, when it doesn't work I get extremely disheartened.

Yesterday I harvested second earlies - Kestral I think and I was over the moon. They were huge and plenty of them. However, today I was checking through them and there's a lot of scab on them. Not on all of them, but I'd say half.

I did some google research and discover it's a bacterial disease in the soil and you can't get rid of it.

Some sources suggest a scab resistant type of potato, others lowering the ph to make the soil more acidic, and some suggest that the problem might not recur if watering is consistent. We did have a very dry spell just as I was down with COVID, so it could have dried out a bit at the wrong time.

I grow my potatoes in a combination of raised beds, and also in large tubs with the bottoms cut out and placed on soil. So a combination between growing in containers with the benefit of the roots being able to go deep into the soil.

Any advice, tips or consolation welcome!!!

 

[Meadowlark]

I've grown in excess of 200 pounds of new potatoes every year since about 1980 in the same garden. I had scab very bad at first but have not had it in decades. Here is what got rid of it:

1) never, ever add manure to your potato row...even composted can be problematic
2) always use Sulphur in the potato hill and on the cuts if you cut them
3) rotate, rotate, rotate...never ever plant potatoes in the same space consecutively...4-year rotation works well for me.
4) always, always follow and precede potatoes with legume cover crops...rye, alfalfa, sunn hemp, clovers etc TILLED into the soil will largely completely prevent scab.

I honestly don't remember the last time I saw scab on my potatoes, and I religiously employ the above practices. It's very easy to be completely scab free.

 

[Susan BBPM]

Awesome! Thanks. Last year we put manure onto the compost heap - I'll avoid doing that again.

I've been looking into cover crops, and I actually have a big bag of clover seed and field beans so I'll give that a go.

4 year rotation will be tricky as we dedicate a lot of beds to potatoes. But I'll work on it!

Big help - thanks.

 

[Susan BBPM]

I've grown in excess of 200 pounds of new potatoes every year since about 1980 in the same garden. I had scab very bad at first but have not had it in decades. Here is what got rid of it:

1) never, ever add manure to your potato row...even composted can be problematic
2) always use Sulphur in the potato hill and on the cuts if you cut them
3) rotate, rotate, rotate...never ever plant potatoes in the same space consecutively...4-year rotation works well for me.
4) always, always follow and precede potatoes with legume cover crops...rye, alfalfa, sunn hemp, clovers etc TILLED into the soil will largely completely prevent scab.

I honestly don't remember the last time I saw scab on my potatoes, and I religiously employ the above practices. It's very easy to be completely scab free.

I've been putting a lot of time, research into this in light of what you said here, and in the discussion on no-till.

It has been extremely useful - and just at the right time when I'm figuring out my planting schedule for the rest of this year and into next year.

I checked over all of my harvested potatoes and those that I thought were OK from earlier harvests do have a tiny bit of scab. The worst effected are the potatoes grown in compost bought from the store.

We've had a dry summer - the potatoes in containers of compost would be most likely to dry out too much. Not sure how the scab bacteria got into the compost though!!

I followed your lead on sulphur - scab likes alkaline soil so making the soil more acid will reduce or even eliminate the scab. I have testing strips and sure enough - the bought compost was slightly alkaline. All of my raised beds are very slightly acid.

As I mentioned on the no-till thread, I think the reason why UK people use compost (rather than chop and drop) is that slugs are a major problem in our climate. So adding compost would be the thing to do here. Whether you dig in or lay it on top - well, no dig people insist laying on top works better, but both work.

And finally, I found reliable sources that say that regular application of garden compost reduces the ph level of your soil.
So by converting what you advise to no-dig in a UK climate laying compost on top of the beds each year should be enough to reduce ph, but I think it makes sense to use the sulphur chips too. I'll keep the manure (we back onto a farm) separate from the compost. The only thing that I'm still swithering over is whether to rotate crops. Certainly I can plant beans before and/or after potatoes - but in the same growing season. If I don't keep beds specifically for potatoes I can't really do no dig!!

I appreciate your input on both threads. This has been one of those discussions that's joined a lot of dots and helped me make sense of umpteen things that I hadn't understood!

 

[Meadowlark]

Excellent discussions. Thank you for the comments. I'm a bit intense about growing my veggies and especially potatoes. It is very important to me to have nutrient dense produce....it is why I garden basically.

Some points:

1) I find the powered ag. sulphur is most effective for me in the garden and specifically on potatoes. You may not have it there.



2) I do use cow manure (home grown) extensively in my garden but never ever freshly applied to a potato row and always at least a year in advance of planting potatoes.


3) Rotation...I do hope you will research this topic further. I'm sure you are aware "The repeated cultivation of potatoes on the same plot of land was one of the primary reasons for the spread of blight that resulted in the Irish potato famine." There are many many references I could give on the need for rotation and recommended rotation cover crops in general and specifically for potatoes.

Again, by doing your homework you will find these and more.

4) I fully recognize climates are different...some vastly so. You have to find what works for you in your location. Accordingly, I like to offer commentary limited to what works for me and, what I actually practice rather than what someone else may do.

Thank you again for being open minded and I encourage you to continue to do your homework.

 

[plot22]

I have grown 2 rows of Kestrel and despite the dry weather I have had a decent crop. I always set my potatoes in a trench on well rotted farm manure and I have a tiny bit of scab. The amount of scab does not really bother me as Kestrel are the most slug and eelworm resistant variety that I have ever grown. Out of the 2 rows I have just harvested I have had no potatoes with any slug or eelworm damage so I am more than happy with this years crop.

 

[Susan BBPM]

That's good to know. I'm trying to work out what to grow next year and was swithering over Kestrel.

One of my goals is to grow 100% free veggies - so completely self sustaining. I saved some of my Kestrel and Desiree harvest last year and used them as seed potatoes this year - I put them in some experimental beds and they came out better than the expensive seed potatoes I purchased.
I've been swithering over whether to save Kestrel seed potatoes for next year. Some of the beds had very little scab and there are plenty of 'clean' spuds for seed potatoes.

Here's what I'm thinking in order to hedge my bets and ensure that I get at least a partial crop in future years.

Swift - First Early

Sarpo Mira - Maincrop that's resistant to everything. They keep growing indefinitely - you can eat them early at new potato size or let them grow until the size you want. They won't stop growing until first frosts.

King Edwards - Because I LOVE them.

Charlotte - Sewn in July for Christmas potatoes.

I've been swithering over whether to include Kestrel, Cara, Desiree (simply because I've harvested lots this year and can save seed potatoes).

All I'd have to buy is a few Sarpo Mira and I'll be (touch wood) eating free potatoes for life!

I am very aware of all the advice to buy seed potatoes every year to avoid introducing disease. But I'm assuming that's primarily from people selling seed potatoes. I'm hoping that if I only save the very best from my harvest I'll be OK?

 

[plot22]

I grew Swift this year along with one row of Lady Cristi which were my own seed. 2 years ago the Scottish potato growers had a very bad crop and since then they have been unobtainable so I have been saving my own seed for one row each year. This morning I have just gone through the Lady Cristi and put to one side enough for 2 rows for next year and fingers crossed I may be able to buy some seed for a third row. I was not too impressed with Swift as they are supposedly the earliest new potato but the one row of Lady Cristi was ready before them and they did not taste nearly as good. Over the years I have tried many different maincrop but now I only grow Harmony (3rows) as they again are eelworm resistant and they do not go down in the water as many main crop do. It's each to his or her own when it comes to choosing potato varieties. I have always saved some potatoes for seed and as Susan says the advice not to save seems to derive from the growers you just have to keep checking the ones you have saved to make sure that you have not saved a bad one.

 

[Oliver Buckle]

I am very aware of all the advice to buy seed potatoes every year to avoid introducing disease. But I'm assuming that's primarily from people selling seed potatoes. I'm hoping that if I only save the very best from my harvest I'll be OK?

The theory is that they are grown in areas where there is no disease, and I think that the advice is old enough that it is not simply hype from people selling seed, but has some validity. I can't grow enough for all our needs, and this year bought seed potatoe which I saw very much reduced, but normally I save the smallest bought potatoes that usually start chitting in the veg cupboard. My logic is that any farmer worth his salt wold not tolerate any disease, it seems to have worked so far.

 

[Susan BBPM]

Out of interest both - how do you store your saved seed potatoes?

I had mine in the fridge last year and that worked fine but obviously isn't ideal as I need the fridge for food!! I've heard some say they just keep them in the shed, but my shed gets baking hot in summer and freezing cold in winter.

 

[Susan BBPM]

3) Rotation...I do hope you will research this topic further. I'm sure you are aware "The repeated cultivation of potatoes on the same plot of land was one of the primary reasons for the spread of blight that resulted in the Irish potato famine." There are many many references I could give on the need for rotation and recommended rotation cover crops in general and specifically for potatoes.

This conversation has helped me understand why so many of the youtube no-dig people grow their potatoes in containers. It made no sense to me, as they all buy in bags of store bought compost which costs a small fortune. It makes potatoes very expensive.

It also explains Charles Dowding's experiments with planting the same crops in the same beds every year (he's on year 6 and thus far no problems).

I now realize that potatoes are the fly in the ointment when it comes to no dig. You MUST dig (or at least significantly disturb the soil) to get your potatoes out.

1. I can't afford (refuse to pay) to buy in compost every year to grow potatoes in. If you make your own you don't really solve the problem as if you've had scab in your garden it'll likely end up in your compost heap.

So, I'm left with:

2. Dedicate a single bed (or beds) to potatoes and grow there every year, leaving the rest no-dig.

or

3. Give up on no dig.

I went out and took another look at my no-dig beds. I have clay soil. To make the beds, I created a wooden frame, placed paper or cardboard on the grass and filled up with bought in compost. I did my first beds last spring. Looking at them now, they all have a few inches of fluffy compost on top, then a harder layer beneath that. The potatoes all grow in the fluffy top layer.

There are very few worms in the fluffy top layer - the worms are in the harder layer, which seems to be the original clay with the compost starting to mix in with it.

The roots of the potatoes go deep into the lower, hard area, and the potatoes nestle in a bed of soft, fluffy, clean compost.

So now I'm wondering if it matters that you disturb/dig the top compost area as that's primarily mulch. A lot of shallow rooting stuff grows in that, but it looks to me like the important stuff is happening in the harder layer?

I think I might try continuing as no dig, but accepting that when potatoes are in a bed I'm going to be rummaging around in the top layer. I might even mix amendments into that top, fluffy layer. But just leave the deep layer well alone?

This will let me rotate my crops whilst still hanging onto the no-dig (which I enjoy). Is this best of both worlds or worst of both worlds?

 

[Oliver Buckle]

I sometimes recommend growing potatoes as a first crop, it can work either of two ways.
I have done it digging the ground over, planting potatoes, earthing them up, and then digging up the crop, disturbing the soil three times like that and growing such a vigorous crop means weeds don't have much of a chance and cleans the ground up well.
I have also done it by taking the weeds down with a sickle, laying down an old wool carpet (Avoid synthetic fibers which don't rot), cutting slits in it, and putting seed potatoes in the slits. The potatoes grow through the slits, the weeds rot under the carpet, and when the potatoes die back and you pull apart the rotting carpet the crop is growing slightly embedded in the ground under it. Not a big crop, but easily gathered. Go over the ground with a rake to get the big bits of carpet and potato weed stalks for the compost heap, or dig them in, as you wish.
@Susan BBPM Have you read about the trick with sugar water on hard earth? I have seen it discussed here but not tried it yet. It involves drenching the ground with water with added molasses, it seems this feeds the ground living micro-organisms to such a degree that they alter the structure of the soil making it soft and friable.
I should have found out earlier, I turned over some of my solid clay last year and left it over winter. In the dry spring it turned into solid lumps and when I tripped coming up the garden I fell on one face first and lost my right eye. It wouldn't have happened if I'd watered it with sugar water

 

[headfullofbees]

Scab is a fungus which which thrives in soil with a pH over 5.5 or if there's too much organic matter in the soil, or if you let the soil go very dry whilst the tubers are bulking up.
Sulphate of Iron is your friend.
Crop rotation is a waste of time, as you will have to seriously lower the pH of your soil to avoid spores which can lay dormant for years, so would still be there when you got round to there again.
Scab is harmless to humans, so a little should be tolerated.
There are also resistant cultivars.

 

[gary350]

Potatoes are a very tricky crop to grow if plants don't get exactly what they need you won't get a good crop of potatoes. Geographical location, weather, soil, fertilizer determines if you have a good crop of potatoes. When I lived in Michigan & Illinois I could throw down 60 potato 1 eye cuttings, rake soil over them, return 4 months later and dig up 300 lbs of potatoes. When I lived in Phoenix AZ plant 60 cuttings Nov 1st return 4 months later dig up 300 lbs of potatoes. Now I live in TN I struggle to get 50 lbs of WHITE potatoes from 60 cuttings. RED potatoes are hot weather potatoes 60 cuttings in TN will grow 200 lbs of potatoes but we like White potatoes better than RED so I don't grow red anymore. Most potatoes are a 4 month crop. A 1 eye cutting, 2 eye cutting, 3 eye cutting all act like 1 plant. I get about 1 lb of white potatoes from each plant in TN that sucks compared to 4 lbs with Red potatoes in TN. Soil needs to be about 5 to 6 ph. Give plants too much nitrogen you get very large plants and very few new potatoes. 5-20-20 is a good potato fertilizer. Soil needs to be very soft for tubers to get large. I till my soil, sprinkle fertilizer in the row, put 60 cuttings in a 40 ft row, rake 2" of soil over the cuttings, this row is finished. When our temperature gets 85°F or hotter plants need shade from 12 noon to dark so I need to plant North South rows so I can use shade cloth for shade. Last year we had 47" of rain Jan to April then desert June to Sept. We don't get much rain June to Sept so I need to water potatoes or there are not many potatoes. If I plant cuttings April 1st they do nothing until weather gets warmer so I wait and plant cuttings April 25 then harvest is about Aug 30. I need to check potato hills once a week to see if I need to sprinkle more soil on the hills to keep sun off of the new potatoes. Daylight we see is blocked by a small amount of soil the sun radiation will go through 1" of soil an new potatoes will be green color. Make sure new potatoes are covered with 2" of soil or mulch.

Be careful with sulfur that stuff stays in my soil for 4 months it kills most everything I plant. I tried adding sulfur in Dec but 47" of rain washes it away by April so now I buy grocery store vinegar by the gallon to pour on my potato rows.

 

[Meadowlark]

... RED potatoes are hot weather potatoes 60 cuttings in TN will grow 200 lbs of potatoes but we like White potatoes better than RED so I don't grow red anymore.

I certainly agree that people should grow what they like and what works in their areas, but my goodness the productivity factor difference on red vs white potato across the Southern U.S. and specifically in my garden is huge. So much so that feed stores in my area do not even carry white seed potatoes, and one would have to special order them around here. White potatoes do not store nearly as well as red for me.

We also harvest 200 lbs of red potatoes every year and they normally last us until close to the next harvest the following year. No synthetic fertilizers are used here on them...rather I rely on soils which were prepared well in advance. For example, see the attached photo of the area that I harvested over 300 ears of corn and my yearly supply of Okra in this spring/summer. Since harvest, that area has been treated with well composted manure and is now planted in the crazy nitrogen fixing Sunn Hemp which will provide easily more than enough nutrients for my red potato crop in 2023. It's important to not use fresh, even if composted, manure on your potato rows during the growing period...or scab will most certainly result.

Next year's potato harvest and onion harvest will be in this soil which hasn't seen either in 4 years.