blighted potatoes

Pests & Pathogens, Root Vegetables

blighted botatoes

I thought the potatoes I dug were fine, even though the plants were heavily hit with late blight. But after three weeks of storage, I have realized they’re not fine. The fingerlings and Russets that were hardest hit and that I cut down and dug first are turning brown and rotting in their bags.

[Late blight produces] characteristic coppery-brown discoloration of the potato flesh under the skin…. Infection of potato tubers arises from spores that develop on foliage. Tubers exposed by soil cracking or erosion of hills may come in contact with spores washed down from infected leaves and stems by rainfall or irrigation. Tubers infected during the growing season may partially decay before harvest. Tuber infection may also occur at harvest when tubers contact living spores remaining on infected vines. Little if any tuber-to-tuber spread of late blight occurs during storage if tubers are kept under cool, well-ventilated conditions. Ohio State Univ Extension Fact Sheet on Late Blight

And here’s a very helpful comment Soilman left me a few days ago:

Blight is a pain, isn’t it?
I’ve given up with tomatoes. I just can’t bear seeing them struck down with blight every year. Potato blight, though, can be managed. I get it every year (it’s a routine hazard in the UK climate), but I’ve never had a crop failure. The key is to remove all the haulms when the blight starts to really get hold.
You then wait at least 10 days before you dig the potatoes; without the haulm, the blight spores get fried in the sun. Choose a warm, dry day to harvest the potatoes. If they’re thoroughly dried before storage, you should be OK. It’s always worked for me. One crucial point: NEVER put potato haulms on the compost heap. Burn them.

And here’s a what the CSA farmer at Piccadilly Farm in southern New Hampshire wrote about late blight yesterday:

A note on the Late Blight front: farmers in all parts of New England are reporting serious losses in potatoes and tomatoes. The spread seems to be snowballing, and any prolonged cool, wet weather exacerbates the problem. We scout daily and have seen no sign of Late Blight here. The tomatoes look great and are beginning to size up. Every passing week means more spuds sizing up and less loss on that crop if we do get the blight here. I know I’ll be counting down the weeks until the relief of that last potato harvest in October (12 weeks…)! Coupling this stress for vegetable growers with the devastating financial crisis that dairy producers are facing, many regional farmers are having a tough go of it.

sliced blighted potatoes

These rotting potatoes were dug right after I cut down the foliage, so I guess that was the error. I have lots of potatoes still in the ground now though I have cut down all of the foliage. Guess I’ll just be patient for a few weeks before harvesting more.

And, someday I need to figure out how to dispose of my compost pile. Its full of blighted tomato and potato foliage. I don’t think anything around here is dry enough to burn. Maybe a big deep hole? I don’t know … Can I just dump it in the woods?

13 Comments. Leave new

  • I'm not sure you would need to get rid of your compost pile. If I understand correctly the spores need live plant tissue to survive. A compost pile to my thinking wouldn't provide that environment. Does your pile get hot? Plus after sitting a year through a cold winter I wonder if that would kill them all?

  • Sorry to see your potatoes – I sympathise. I too have dug them immediately after cutting the haulms, with no ill effect. Having said that, I only ever harvest potatoes on a bright sunny day and leave them sitting in the sun for a few hours to dry off – it could be they were too wet and stayed that way? Or maybe you waited too long – the blight travels down into the potatoes from the leaves. It's always a gamble, I'm afraid.

  • There's plenty of living organisms in a compost pile, and if you compost your scraps back into your garden I wouldn't think it's safe to compost them.

    According to Cornell Horticulture, here's the procedure:

    "Be prepared to destroy your plants when late blight starts to become severe. Seal them in a plastic bag. Do not put them in the compost pile. Leave the bag ‘cooking’ in sunlight for several hours to kill plant and pathogen, then put in the trash."

    As for whether you can "just dump it in the woods," that's the kind of NIMBY thinking which has caused major environmental destruction in the past. It might be okay, but it might not, you know?

  • Blight spores can probably only live for 3-4 years without a host, so a deep hole sounds like a pretty good solution, as long as it won't be disturbed for at least that long.

    Since you have two gardens, you could also use the compost on one of them as long as you don't use the space for tomatoes or potatoes for a few years.

    The biggest problem is the rain can splash the spores up onto the leaves of the plants, so you want to be sure to keep the contaminated compost away from plants that can become infected.

  • Patrick,

    That's what I was thinking of doing – using the contaminated compost next year in my community garden plot, and going without tomatoes there. That's why I've been saving the compost. Plus its a large volume to dispose of and I don't want to waste so many plastic bags and time dragging it home with me to the trash.

    I can't really see having to energy to dig a big hole.

    But I think other gardeners aren't thrilled with this plan as they want to grow tomatoes and potatoes nearby. I have horrified gotten looks when I tell people whats in the bin.

    But I think its silly for me to plant tomatoes in my plot next year after two years of near total failure.

    And I'm not sure there any point to me going to the effort to reduce spores in my plot unless there is a strict policy in place at the community gardens that everyone abides by. (And I'd really prefer not to have Rules at the gardens.) Absent that, I think I'll take the easier route and save my compost.

    I suspect, as Soilman says, that blight is more manageable with potatoes. Especially using resistant varieties. But then, I wonder if growing potatoes perpetuates the spores? So I'm not really looking at it as year or two of going tomato-free to eliminate the problem. I think its a problem that's here to stay. It just goes along with the weather pattern.

    The only solutions I see are 1- hope for a different weather pattern, or 2- use strong proactive fungicides, or 3- only grow tomatoes in isolation.

    So I think next year I'll only have my private tomatoes tucked away in my backyard. I was interested to hear that the organic Farm I distribute CSA shares for (Picadilly Farm) is going to hoop house production for their tomatoes next year.

    I hope you have good success with you blight resistant breeding! That would be super. I'd like to request a resistant Brandywine. I'd be really glad to test any for you!

  • Kathy,

    You are right that blight is more of a collective issue than an individual one. If however you are planning to grow potatoes on your plot, even though blight can be managed in the way Soilman says, it's still critical to do everything you can to reduce the number of spores in the area. A week or two difference in when your plants get infected will make all the difference between success and failure, and your plants will probably get infected earlier if your garden is full of spores. For this reason it's also critical you rotate where you plant your potatoes and tomatoes.

    If your plot is also very full of spores, they can spread to neighboring gardens by wind or carried on the bottoms of shoes. Your garden neighbors have good reason to be concerned about your composting your potato and tomato waste.

    Community garden management always has the issue that people give up their gardens from time to time, and it's important that problems like this are not left behind for the next gardener. For this reason it's not unreasonable for your garden's management or the other gardeners to be specially concerned with the situation.

    Here in the Netherlands it's illegal to plant potatoes or tomatoes on the same spot more than once in three years, and you are also legally obliged to remove infected plant waste. It's the same in most neighboring countries as well. It's worth pointing out a lot of people question the validity of these laws, but they are there.

    At the same time, every year when I get blight in my garden, it's always a matter of extremes. For example, while I always remove infected plants, the contamination is always more widespread. For example, small pieces of infected plants get left behind and mixed in with weeds or the straw I use as mulch. If I get blight in my greenhouse, it always needs to be decontaminated with a disinfectant like bleach.

    What I do with material that has been contaminated with spores, but are not themselves infected plants, is compost them separately in a closed plastic container and use the compost in a place not used for tomatoes or potatoes, like perennial bushes or a similar place.

    It's really important to do everything possible to take care of infected material and practice good hygiene.

    At the same time, the practical side of things is that if plants are not infected they are not hosts. It doesn't 'hurt' anything to grow potatoes or tomatoes, as long as they don't get infected or you take care of them quickly when they do. Spores last 3-4 years, so if you do have contaminated material at least this old, it is safe to use again.

  • oh Kathy what a shame :o( we're forecast yet more rain here in the UK next week so I'm keeping my fingers crossed that mine won't be effected while I'm not at home to dig them up. Thanks for posting the tips – here's hoping I won't need them.
    Nic x

  • So sorry to hear about your potatoes and tomatoes. I agree with the other posts, I don't think it's the best idea to save that compost – especially since it's at a community garden where others may still want to grow tomatoes and potatoes next year. I know it's a lot of work to move it and to dispose of it properly, but things like that are the price we pay for having a garden.

  • I agree, you are in a tricky situation. I think you owe the community garden the respect of practicing proper garden management, however, at the same time whats done is done and now it is matter of deciding the best way to go forward. There must be a reasonable solution out there, you can't be the only one to have used this method of disposal.

  • Do you have a part of your yard with just ornamental plants, shrubs, etc.? Maybe you could use the compost there. I think the late blight is specific to plants in the nightshade family so the flower garden should be okay and not perpetuate the disease. Probably should check this out first.

  • OK, so I think my plan now is two parts:

    1. Remove my late blight contaminated compost pile this week into plastic trash bags and dispose of it in the trash. I figure about 3-4 bags. Shovel it in, drag it home in my trunk. Trash pick up is Tuesday. Its a one step solution.

    2. Post a notice about Late Blight at the community garden entrance. (I've been trying to find an expert to come give us a presentation, mostly as a social event, but in the meantime I could post a quick sign). I'm working on a draft summarizing the info above.

  • Kathy,

    Many thanks for this extremely valuable thread. I returned home from a vacation at Wood Hole on the Cape to find my potatoes infected with blight. My tomatoes however look hale and hardy- not a spot. So, based on the excellent advice I've read here, I'm planning on cutting the potato foliage to ground level, bagging the waste in plastic bags, waiting a couple of weeks until we get a dry sunny day and then harvesting the tubers (with my fingers crossed). My question is- since my tomatoes look fine, should I just sit tight, or should I take some kind of preventative action. I haven't used any fungicides or pesticides on my garden to date, as such things have not been needed so far. However, I might consider using such things to save my tomatoes! (you can see my priorities here 😉

    Thanks for all your help,
    Michael in Durham CT

  • Hi Michael, I would spray your tomatoes with Copper spray or Serenade. I'm Using Copper soap spray and it does seem to help. They aren't "organic", but are approved for use by organic certified farms against Late Blight. good luck.


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