The Potato Growers' Curse

by frankbeswick

Potato blight [Late Blight] is a serious threat to crops across the world, and it is not just potatoes that are endangered.

The 1840s were hard years for Ireland, a country whose population relied on the potato for sustenance. For several years the weather conditions in mid to late summer had been damp and cool, the conditions which blight, the fungus Phytophthera infestans thrives. The first signs were brown blotches on the leaves, which then shriveled.The trouble was that the fungus got to the tubers, which rotted within a few days of picking, causing mass starvation. All that is history, but the disease still thrives and is enjoying a come back in the wet and cool summer that Britain has been having.

Photo courtesy of wait0000, creative commons

The Blight Arrives

I should have seen it coming,or maybe foreseen is the better word,  for you cannot see the blight arrive, its microscopic oospores float unseen on the breeze till they find a host.But its menace can be foreseen,  for we know the conditions in which it thrives. The fungus reproduces by oospores, which are water-borne, not in deep water, but the thin surface lubrication that occurs in long term damp conditions, and that's what we have had in Britain this year,  a steady succession of rainy days and temperatures that are a disappointment to holiday makers. We  have not had a good summer, but the fungus  loves it.

The speed at which the fungus arrived was dramatic. I had had my eye on the potato bed and nothing seemed to be wrong, but  I was fortunate to enlist the services of my neighbours, the Keane Brothers, a pair who have not only years of  experience in gardening but have won many prizes, to help me to move a greenhouse. They have the plot next to mine;my other neighbour is a judge in gardening competitions, so I have talented  people on both sides .It was one of the brothers who told me that he had discovered blight on his plot. A quick scan showed me that a few leaves on mine were showing symptoms,leaves which had dark blotches and which later turn brown and crinkly before they shrivel. I decided that I was coming back the next day to clear the infected plants. 

Before I arrived I expected the job to be short, but soon the gravity of the situation hit me. There was far more blight than I thought. Don't be too concerned, as there  were many plants that were unaffected, but there were enough for me to know that this is the worst blight infestation that I have ever suffered.

But I had to manage my garden work carefully. Before I dealt with the potatoes I watered the plants in the greenhouse, so I could approach them with unsullied hands, and I had to be careful. I have peppers, egg plants and tomatoes, all of which are members of the Solanaceae family. It is the Solanaceae that are vulnerable to blight, so I ensured that I did not enter the greenhouse after I had begun the clearance, until I had finished and washed my hands thoroughly.   

What to do.

After I was informed that blight had arrived I drove to the garden centre to buy some Bordeaux mixture, only to discover that this  traditional remedy has been taken out of service by European Union legislation. At this point I imagine the scurrilous anti-EU press trumpeting a headline,EU attacks our potatoes! They missed this one,  but there was a reason behind the ban.Bordeaux mixture is composed of copper and slaked lime, but over the years in which it has been applied to soils on farms there has been an accumulation of copper in soils, leading to some toxicity. In excess copper does no good for soil life, such as worms. You can still purchase copper sulphate, but the garden centre  had none in stock. However, knowing the need for copper to  destroy the fungus I ordered some online when I returned home, express delivery. By the time that I am writing this sentence the copper sulphate has arrived, but the weather is wet and I will need a dry day to apply it. I am unconcerned about toxicity, for I have not overused copper as some farmers have, so my soil is not in danger of having too much of it.

But my neighbour, Ron, the gardening competition judge, had already acted. His potato crop is small and well tended, so he simply lopped off the tops of all the potatoes and dug them up.  Doing this when you see the first sign of blight means that you kill the  infected  leaves before the fungus drops its spores into the soil. If you do this the potatoes are unaffected and are, though smaller than you hoped, perfectly edible. I checked a few of mine by digging them up, and found that they are small, the size of new potatoes, but are fine. I sought  Ron's advice, and he suggested that as the infection was not present in all my crop,I monitor it and eliminate only infected plants. 

Not all varieties are affected.First and second earlies rarely suffer, but main crop can get the disease badly. The Irish potato famine occurred because the Irish peasants grew a variety called the Lumper, which was a large, starchy,flavourless variety that sold well to the mass market of the English poor. The Lumper was very prone to blight, so Ireland took the full force of the disease. No one grows it now.  Some varieties are bred for resistance, but the pathogen can mutate and so no one is really secure. 

One important rule. When you rip up the infected plants, do not compost them on your garden compost heap. I took mine to the council tip [garbage disposal centre] and put them in the green waste section. The council works with a recycling company that has a hot composter, which  is a tunnel into which the green waste is shoved. The heat inside is so great that break down of tissues is achieved more easily than the domestic compost heap can achieve, so the pathogen dies with the plant tissue,whereas in the domestic heap  it can live on to infect more ground.

Long Term Precautions

To protect my tomatoes, egg plants and peppers I am ensuring that when I water them I pour the water directly onto the soil so that the leaves do not get wet, as the pathogen is water-borne. As always good ventilation is an enemy of fungal attacks, and though I want to keep the Phytophthera spores out, stale air can encourage mildew and botrytis, also nasty fungal infections.A careful inspection regime will be necessary, and I hope that the weather will become drier and warmer. We have not had a great summer.

For next year a good crop rotation will be necessary, and no potatoes will be grown on ground on which infected plants were found. This is going to cause me a problem as I have grown potatoes for years, but the answer may lie in my intention to use more raised beds and containers. I am thinking that next year I will grow potatoes in containers, pots using fresh compost rather than relying on the underlying soil.This may have to be the case for some years, and I will refresh the compost every year. Also necessary will be for me to spray with copper sulphate early in the season. I have not had to do that before, but the need is on me me now.

Furthermore, a more careful selection of varieties will be needed, so I will avoid any main crop potatoes in favour of first and second earlies, and choose varieties with good fungal  resistance.

Also important in your anti-blight strategy is to ruthlessly pull up any scutch potatoes that survive until the next year.These grow from potato tubers left accidentally in the ground after picking, but while you might be tempted to regard them as  an extra crop, beware, potatoes are a disease prone plant and so these tubers can harbour viruses and fungi that can infect the soil.Blight can and does dwell in these roots, so be safe, get rid. Compost them not on your heap but in the council waste disposal unit, and if there is no such hot composting unit available to you, burn them. 

Don't be too concerned, not all my crop is affected, and much survives, the same goes  for Britain's crops of potatoes. But climate change is giving us erratic summers, so no one can predict what is coming next year. All that I can say is that next year I will be more ready than I was this year, and the experience will accelerate my progress towards raised beds and containers for vulnerable plants.





Updated: 07/08/2016, frankbeswick
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frankbeswick on 07/13/2016

Fungal infection can affect experts. Monty Don, an expert gardener who presents the television programme Gardener's World, someone whose advice I value, lost his box hedges to box blight.All he could do was rip them up and replace them with other species.

frankbeswick on 07/13/2016

Sadly, the blight got into the greenhouse. The speed at which it arrived was unsettling.One day, just a few symptoms, next day, despite spraying,it was all on one side. I sprayed again and thinned out unproductive stems to allow air in. My aim is to preserve the tomatoes. We might be in line for some decent weather in the next day or two, which might help.

blackspanielgallery on 07/12/2016

Gardening, as with other things, requires knowledge. You are ahead of many by knowing what is happening and taking act.

frankbeswick on 07/11/2016

I saw a few smitten leaves in the greenhouse, but this time I had the time to act, so today I gave the whole set of plants a good spraying with copper sulphate. But greenhouse work was all that I could do today, as the weather is very wet.

frankbeswick on 07/09/2016

The disease dwells in living tissue and dies quickly outside it, but potatoes are often left in the ground after picking, as some are missed by the picker, so the pathogen can linger in the tubers, if it has got into the soil. I think a year will be enough if the disease is caught and treated early, but otherwise two years or more might be necessary, as it will take that amount of time to guarantee that scutch potatoes that are acting as pathogen reservoir are destroyed.

I read an article today by Charles Dowding, an expert, who thinks that the pathogen will die in a garden compost heap, as the living tissue in which it is embedded is decomposed, but I am not totally convinced, so I prefer hot composting just to make sure.

dustytoes on 07/09/2016

How long does it take for the disease to be gone from the soil altogether? Is a year's wait long enough?

frankbeswick on 07/09/2016

Well,I am going to grow potatoes in containers with fresh soil, though I am placing them on the opposite side of the garden to the infected area. Butt in the area which has been most badly it, which is one bed in particular, I may grow make a three sisters bed, which is maize, pumpkin and beans grown as companion plants.

dustytoes on 07/09/2016

I had tomato blight a few years ago and lost my lovely crop. What will you plant in the infected garden area next year?

frankbeswick on 07/09/2016

I think that next year I will grow the tomatoes in my new greenhouse, which is further away from the blight afflicted area than my first greenhouse is. I will use greenhouse number one for plants that are not susceptible to blight, maybe using it primarily for bringing on seedlings. Playing safe,really.

However,what did I just say about digging up the potatoes? The weather here is very wet, it has not stopped raining all day, so there is little gardening being done.

frankbeswick on 07/09/2016

Today I am finishing the job of clearing the affected bed, then I am digging up the potatoes, as they won;t grow after the plants are gone. But they will still be healthy and edible.

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