more on late blight

Pests & Pathogens, Tomatoes

Late blight seem to be the only conversation topic I hear this week at our community gardens. I hear yelling from across the way about newly discovered dead tomato plants. I hear long technical discussions among groups of gardeners.

And everyone spends a fair amount of time walking around and looking at tomato and potato plants in other plots. People come by my plot to chat and they know whose plants look good and whose are dead. They remind me that I should be bagging and destroying the foliage so it doesn’t infect everyone else’s plants, which, of course are all already infected or dead or coated with fungicide.

And there are stories circulating about who has pulled everything, who won’t pull anything, who’s bagging and disposing, and, probably one about me just throwing my dead plants into my compost bin.

I heard someone dug up a whole row of potatoes that were just mush from blight.

I emailed the extension school yesterday to see if there any experts who could come talk to us. With so much interest, I think it would be a good way to get the gardeners together, though we can be an unruly bunch. We could have a nice relaxing coffee and donuts gathering, in a freshly mowed grassy area with beautiful mid summer flowers, singing birds, and listen to tomato gloom and doom stories….

An article on Late Blight is in yesterday’s New York Times: “Outbreak of Fungus Threatens Tomato Crop” :

“A highly contagious fungus that destroys tomato plants has quickly spread to nearly every state in the Northeast and the mid-Atlantic, and the weather over the next week may determine … whether tomato crops are ruined…. described as an “explosive” rate of infection…..William Fry, a professor of plant pathology at Cornell, said, “I’ve never seen this on such a wide scale.”

“The current outbreak is believed to have spread from plants in garden stores to backyard gardens and commercial fields…. Some growers are talking about $40 boxes already.”

Some facts I’ve learned about late blight:
– Lat Blight was responsible for the Irish potato famine of the mid-19th century.
– It is one of the few plant diseases that can destroy an entire crop.
– The disease can wipe out entire tomato and potato fields within a week if conditions are wet.
– Late blight spores can travel over 40 miles under the right conditions.
– Powerful synthetic fungicides like chlorothalonil (not approved for organic farming) can protect unaffected plants from disease, but can’t cure infected ones.
– Copper fungicides are officially listed as synthetics but organic certified farmers are allowed to use these after they have used all available alternative practices to manage late blight.
– Copper fungicides extend potato growing period by between 2-4 weeks…. estimated to result in 10 – 40% higher yields.
– Potato varieties with moderate levels of resistance include: Kennebec, Sebago, Allegany, and Rosa. Elba is currently the most resistant potato variety available.
– Few late blight resistant tomato varieties are available. The cultivar ‘Legend’ has some resistance, though not under high disease pressure. Some cherry tomato cultivars (‘Red Cherry’ and ‘Sweetie’) are more tolerant to late blight. ‘Matt’s Wild Cherry’ is considered resistant.
– If late blight occurs when potatoes tubers have already ‘sized up’, harvest crop as soon as possible to avoid post-harvest tuber rot.
– Tubers become infected when spores wash down through the soil and come into contact with the potatoes. Tubers are not infected via their connection to plants with blighted foliage.
– Occasionally peppers and eggplants are mildly infected, as are a few nightshade weeds.

Fungicides for late blight on potatoes
Cornell University fact sheet on Late Blight

9 Comments. Leave new

  • I'm sorry you are having such problems with late blight this year. Last year was a bad one for us, but no sign of it yet this year. I guess it all depends on the weather conditions.

    Tom Wagner ( is a public domain plant breeder and has developed quite a number of totally blight resistant potato varieties. I expect they will be released in the next few years, or maybe you can contact him directly and get some now, I'm not sure.

    Tom has even created several totally blight resistant 'Lumper' varieties. The Lumper potato was the one most widely grown at the time of the Irish Potato Famine.

    It's particularly significant Tom has produced public domain blight resistant varieties, because the big seed companies has been claiming until now the only way to create blight resistant varieties was with GM techniques. Tom has proved them wrong.

    Tom is touring Europe this year promoting his work on potatoes.

    I will start work next year on some blight resistant tomatoes, but it's worth mentioning many people before me have tried and failed, and blight strains are very regional and rapidly evolving things. If I am successful it may only be for a few years and it may only apply to tomatoes grown in Europe.

    Some wild or currant tomatoes have resistance, and in particular the two being grown by a number of people in Europe this year are 'Tomatito de Jalapa' and 'Humboltii'. Both are said to have a high degree of blight resistance in Europe.

    Matt's Wild Cherry also has some resistance, but tends to get blight anyway even though it continues to produce tomatoes, meaning it's infecting other plants at the same time.

  • Thank you for your great post. It's very timely for me. I've been on the look out for late blight in my garden for the past few weeks and just noticed what I think is some on my potatoes this afternoon. I'll be going out tomorrow morning and yanking them up. They are only just now flowering so I don't think we'll have any potatoes. Oh well.

    I was looking at the forecast for Delaware today: rain Monday to the following Monday! Egads. I imagine my tomatoes which have been suffering a little from early blight will now succumb to late blight 🙁

    The ups and downs of gardening are what keep it exciting. Keep up with the great posts and the beautiful gardening.

  • Why are you choosing to dispose of the diseased plants in your compost pile rather than the bag method? (Do you feel the disease is so widespread that it just doesn't matter?)

    Is anyone talking about what the future impact of this breakout will be on the gardens? All articles seem to be stressing the importance of keeping it contained as to not infect commercial growers, but not much is mentioned about next season. I am under the impression that it may be a fresh start next year providing no newly infected plants are introduced?

    I hope the extension will do the talk for you, best of luck with all of it!

  • The colorful garden gates make me smile…we don't have a community garden…maybe I'll start one someday!

  • Hiya

    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.

  • Dawnie (CT)
    July 22, 2009 4:23 AM

    I was out early this AM in the drizzle staking some of my tomato plants….still no sign of blight. I'm still keeping my fingers crossed!!

  • Hi Kathy
    I just wanted to thank you for sharing your beatiful garden with us. I found your site while searching for tomato growing tips in Massachusetts. I have not had a garden for years and I wanted to get some helpful advice. I enjoy checking in every other day or so to see what is happening. I love that you share your pictures and your knowledge of what is going on in the garden world locally. I have similar issues with my garden and you have been a informative guide and support for me. I only recently started gardening again and I am already planning for something better next year. I enjoy your humor, upbeat additude, and of course, Skippy!
    Thanks for you time and effort to share your gardening with us.
    Your garden is a dream place!

    Best wishes, Nonni

  • I'm sorry for your potato problems. Were you able to salvage some of them to eat?

    I need to learn more about the different diseases on tomatoes and potatoes. We live in the house my husband grew up in. His mother had died 7 years before we moved in. When I was out cleaning up the garden space, a neighbor came over and told me I wouldn't be able to grow tomatoes, because there was disease in the soil. Well, he was right, but I plant them anyway, and get a harvest before the disease kills them.

    My potatoes across the street are starting to die back, but I think it's because they are finished, but I'm not sure. The edges of the leaves are turning brownish. The potatoes the neighbor boy and I dug looked good. I hope they are.

  • I recently came accross your blog and have been reading along. I thought I would leave my first comment. I dont know what to say except that I have enjoyed reading. Nice blog. I will keep visiting this blog very often.



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