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Potato blight, how to treat Phytophthora infestans.


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James Kilkelly
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PostPosted: Fri Mar 28, 2008 1:12 am    Post subject: Potato blight, how to treat Phytophthora infestans. Reply with quote

Potato blight, how to treat Phytophthora infestans.
by GPI

Potato blight (Phytophthora infestans) thrives and multiplies at an alarming rate in mild & damp climates; It's no wonder then that this is the main problem experienced by Irish potato gardeners. The first signs of blight are brown spots on the leaf tips of the potato plants, often but not always accompanied by a fluffy white fungal growth.
Following on from this, the foliage will begin to rot, calling a premature halt to the growth of the potatoes. To make matters worse, fungal spores drop from the leaves onto the soil, where they quickly infect the potatoes rendering them inedible with dark sunken areas on the potato skin and a bronze rotting of the flesh.

Potato blight Scientific classification.
Domain: Eukaryota
Kingdom: Chromalveolata
Phylum: Heterokontophyta
Class: Oomycetes
Order: Peronosporales
Family: Pythiaceae
Genus: Phytophthora
Species: P. infestans
Binomial name
Phytophthora infestans

An example of blight affected potato leaves and tubers, photo / picture / image.

Management of the problem organically.
Arrow 1. When digging your potatoes each year, you should be scrupulous in clearing your soil of all potato tubers, even those as small as pebble. Ensure that there are no potatoes on site from last years growing, as blight spreads by fungal spores from old potatoes to new crops in mid-summer. Placing potato peelings on your compost heap can also carry over blight if the heap is not hot enough, so I would also avoid this.

Arrow 2. Plant only blight-free certified seed potatoes into soil that has not grown potatoes for at least three years. If you forget about planting maincrop potatoes altogether and instead opt for a first early or second early variety, this will allow you to harvest before blight infection is at its highest (mid -summer onwards). "Colleen" and "Orla" are both early potato varieties with good blight resistance.

If you are going to grow maincrop potatoes (harvest-August/September) then I suggest you select a common variety with strong blight resistance such as "Cara".

Some of the more blight susceptible potatoes to avoid are.....
Maris Piper ,
Arran Comet,
Arran Pilot,
Desiree
Epicure,
Foremost,
Golden Wonder,
'Home Guard',
Kerr's Pink,
Majestic,
Sharpe's Express,
Ulster Chieftain.

Reassuringly, one of the greatest hopes in the search for blight free potatoes has been the recent introduction of the Hungarian Sarpo varieties, "Mira" and "Axona". Promising four times more blight resistance than any variety already available, I have heard great reports about these maincrops including boasts of high yields and a floury texture.

Arrow 3. Avoid overhead watering of your potato crop, as this tends to wash the fungal blight spores from the potato plants leaves down into the soil, to infect the tubers. Of course, the rain will do this naturally, but if you have to provide additional irrigation, then I suggest you water the soil not the foliage.

Arrow 4. When the weather conditions are conducive to the spread of blight, radio stations and daily newspapers will issue "blight warnings", so watch out for these. Upon hearing a blight warning you can apply an "organic" blight spray known as Burgundy mixture, this is not a totally organic spray, but is a deemed acceptable by most organic growers.

Burgundy mixture is created by mixing......
50 grammes of copper sulphate (bluestone)
60 grammes of sodium carbonate (washing soda) or sodium bicarbonate (baking soda)
All in five litres of water.

As a prevention before blight symptoms show, you can spray this mixture on to your potato foliage every seven days during blight warnings, ensuring that the undersides of the leaves are coated as well.

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Arrow 5. Herbal teas concocted from common weeds/herbs such as nettle, horsetail (Equisetum arvense ) and comfrey can be sprayed on potato foliage to help prevent the spread of blight disease.

To make the horsetail tea you should ideally in early summer pick the green part of the plant, leaves and stem, excluding the root. You will need one kilogram (2 ΒΌ pounds) of equisetum to submerge in drum filled with 20 litres of rain water, stirring it daily over three or four weeks.

When the time comes, mix it in your watering can at a rate of ten parts water to one part horsetail tea, then water liberally onto your plants. Plants that show any symptoms of bight or other fungal type disease should be sprayed with this mix once every four days.

If in a rush to create a batch of horsetail tea, you can make up some by simmering 1/2 kilogram of the weed in a pot with 10 litres of rain water for about an hour. Once cooled it should again be mixed it in your watering can at a rate of ten parts water to one part horsetail tea.

Arrow 6. Be blight aware by checking the leaves of your crop daily, especially when the risk is high during July and August, at these times the disease can appear literally overnight. If you find blight on the foliage and you anticipate your potato yield is acceptable, then I would "bite the bullet" and cut away the stalks. Wait for about two weeks, then using a garden fork, gently loosen the potatoes from the ground discarding the few that the blight may have reached.

Management of the problem chemically.
All the measures mentioned above still stand, but instead of the Burgundy mixture many gardeners prefer to use stronger preventative blight sprays such as Bio Dithane945 or other fungicides containing the active ingredient Mancozeb.

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So, here's hoping for a dry summer and little blight.

Associated content.....
Nettle fertiliser, How to Brew your own.

Grow your own potatoes.

Increasing your stock of seed pototoes, How-to Video.

How to chit seed potatoes for earlier and heavier cropping.

How to grow new potatoes for Christmas.

How to manage the top two potato pests, Wireworm and Slugs.

Common potato Scab, Management of the problem.

Planning a Vegetable Garden? How to Make a Vegetable Garden.

(DISCLAIMER: The control methods are suggested here as a matter of general information. Under Irish and EU law it is illegal to use any preparation as a pesticide/fugicide/herbicide that is not approved for such use. The author and the website accepts no responsibility for how a user may mix, use, store, or any effects the mixture or its elements may have on people, plants or the environment. The information here is for reference only and does not imply a recommendation for use. If you disregard this warning and make any of the preparations you do so entirely at your own risk.

Any queries or comments on common potato blight, please post below.

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Last edited by James Kilkelly on Sun May 16, 2010 4:30 pm; edited 2 times in total
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Fiachra
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PostPosted: Tue Jun 30, 2009 9:39 pm    Post subject: Reply with quote

Thanks for all the information for novice gardeners like me.Is there a picture of horsetail anywhere on the site?
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James Kilkelly
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PostPosted: Wed Jul 01, 2009 1:09 am    Post subject: Reply with quote

Fiachra wrote:
Thanks for all the information for novice gardeners like me.Is there a picture of horsetail anywhere on the site?



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Fiachra
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PostPosted: Sun Jul 05, 2009 4:32 pm    Post subject: Reply with quote

Thanks,Where would you find it - it looks like something you would see in the woods?
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PostPosted: Sun Jul 05, 2009 5:39 pm    Post subject: Reply with quote

Hedgerows, edges of woods, stream-sides, pond-sides, it likes moisture especially.
Bill.

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James Kilkelly
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PostPosted: Mon Jul 06, 2009 12:24 am    Post subject: Reply with quote

Spot on.
The bog is where I see most of them.

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Fiachra
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PostPosted: Mon Jul 06, 2009 9:20 am    Post subject: Reply with quote

Thanks Lads,
I'll be visting my parents at the weekend - plenty of wet boggy land where they live so I'll have a look!
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PostPosted: Mon Jul 06, 2009 11:20 am    Post subject: Reply with quote

It sounds like you're thinking about planting them in your garden Fiachra. They can be a real pest if they spread - take a look at the roots in the pic. Impossible to get rid of!
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Mavericka74
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PostPosted: Mon Jul 06, 2009 11:40 am    Post subject: Reply with quote

Hi All,

Just looking for some advice. I planted Red duke of york 1st earlies which I dug up 2 days ago. They seem fine but the leaves were turning yellow and then withering over a period of time (2-3 weeks). When I dug up the potatoes the original seed appeared to have gone rotten but the potatoes look fine. Should I be worried (is it blight). I also have some main crop Kerr Pinks and the leaves are turning yellow on them too but its probably to early to dig them up. I was told it could be lack of nutrients thats turning the leaves yellow.

What do you think? Is it blight or what? Are the the Red Duke of York ok to eat. They look fine?

Cheers

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Liparis
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PostPosted: Mon Jul 06, 2009 11:51 am    Post subject: Reply with quote

For goodness sake, don't plant the stuff in your garden. You will find it everywhere even pushing up through tarmac!

Mavericka74, I answered your post in the other thread. I wouldn't double post, it will cause broblems collating everyones advice.
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verge
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PostPosted: Mon Jul 06, 2009 11:57 am    Post subject: Reply with quote

Liparis wrote:


Mavericka74, I answered your post in the other thread. I wouldn't double post, it will cause broblems collating everyones advice.
Bill.


As it has already. Rolling Eyes
Thanks for answering the query Liparis. I had removed the post by Mavericka74 just before you posted so it it ended up your post looked out of context, so I removed it as well.

Here is the Liparis reply in full Mavericka74.
Your original seed potato has done it's job, it's life cycle is finished. It's quite normal for it to rot, although on ocassions they don't. If the potatoes your lifting aren't showing signs of blight then it's possibly a nutrient problem. try a general fertiliser like Phostrogen, that will get ito them quicker, or a granular like growmore.
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PostPosted: Mon Jul 06, 2009 1:18 pm    Post subject: Reply with quote

Thanks for that.


I didn't mean to post twice. I had two windows open at same time and posted my question on wrong one. My mistake. Thanks for sorting it out for me.

I spread some 7.6.17 fertilizer on the soil around my potatoes. I was told it was the right stuff to use. Will it do the job? I also noticed some small flowers on the main crop potatoes a few weeks ago but they only lasted a matter of days. You can still see where the flowers were but no flowers there now. Is it possible that they are ready for digging as well. they are main crop kerr pinks.

Thanks again

Mav
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PostPosted: Mon Jul 06, 2009 3:09 pm    Post subject: Reply with quote

The presence of blossom on the stalk is no indicator of stage of maturity of tubers. kerrs Pink though regarded as a main crop can be grown as second earlies and do quite well in good sunny situations but they are very susceptible to blight, Try a sample stalk for a test or just root into the soil and try and pick a potato off the stalk without pulling it up. if potatoes come off stalk easily as stalk is turning yellow then they are fir to dig.
michael brenock horticultural adviser (retired)
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Her Outdoors
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PostPosted: Mon Jul 06, 2009 9:58 pm    Post subject: Reply with quote

[quote="Liparis"]For goodness sake, don't plant the stuff in your garden. You will find it everywhere even pushing up through tarmac!

This is the worst weed you can have in your garden! We got a couple of loads of soil when we first started the garden in 2005. The soil was great quality - except - it was full of horsetail, which we had no experience of. We have learned a lot since then. I spend half my time pulling it up and it has the flimsiest roots, you never get to the bottom of it. As Liparis said, it will even come up in tarmac! Steer clear of it.

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PostPosted: Wed Jul 08, 2009 11:47 am    Post subject: Reply with quote

Hi everybody,
Realx! I was just going to pick some to make the anti-blight tea.
Thanks anyway
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