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Information and discussion for successfully cultivating potatoes, the world's fourth largest crop.

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Old July 4, 2018   #1
Eric02476
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Default Can you identify this aggressive foliar disease?

I'm stumped. Does't look or act like Alternaria or Early Blight but I've never had significant disease problems with potatoes so I am much less familiar with what they look like on this crop. Fungal, bacterial, or viral? And is there any point to spraying?

I grew all King Harry this year because of heavy losses from potato leafhopper the past 2 seasons. Well, I haven't noticed leafhoppers or hopperburn damage, but this disease started about a week ago, slowly, and in the past 2 days it's rampaging. First there's yellowing and specks, then browning of the veins, and then the leaf starts to die. Ugly.

I did spray Daconil 2 days ago when it became clear this was more than a nuisance but I know that's too late. I have Copper, BioSafe and potassium bicarb sprays on hand if you think it would do any good. But the main question is whether this is something so virulent that it threatens my tomatoes, which are in noncontiguous beds about 10-15 feet away. Hate to sacrifice the potato crop now but if they're goners anyway, maybe I will.

Eric
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File Type: jpg potato leaf 4.jpg (220.2 KB, 136 views)
File Type: jpg potato leaf 5.jpg (175.8 KB, 137 views)
File Type: jpg potato leaf 6.jpg (241.7 KB, 138 views)

Last edited by Eric02476; July 4, 2018 at 05:35 PM. Reason: photos
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Old July 5, 2018   #2
greenthumbomaha
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I'm sorry that I can't help you, but bumping so more people will see this.

Is there a local Extension office that you could contact for information?
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Old July 5, 2018   #3
brownrexx
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I grow potatoes every year but thankfully have never seen that. Sorry but I don't know what it is.
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Old July 5, 2018   #4
Eric02476
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Thanks to you both - bumping (and sympathy) is most welcome. The state extension agency here in Massachusetts doesn't do much consultation for home growers, although I could pay for a lab test. Still, I might drop them a line.

The potatoes this morning continue to show sharp decline. Whatever this is, it's virulent and I fear I will lose most or all of the crop. I'm astonished with how quickly it moved - it went from "oh, looks like I might have some minor leaf blight but it's been dry so probably no biggie" to full-on assault in just 2 to 3 days.

Of course I've done a lot of Google text and image searching and haven't turned up a lot that really matches. Some images of various potato viruses look similar. I know a few things it's not: Alternaria, Early Blight, Late Blight, Septoria. I don't think it's simply powdery mildew - don't see any powder - although since the weather's been hot and dry I have considered it. Don't know how it manifests on potato. I did spray potassium bicarb (Green Cure) yesterday just in case that's it - might slow it down enough to get a little harvest. That stuff is only mildly effective on most diseases but great for PM.
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Old July 5, 2018   #5
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My first guess was Late Blight but you wrote that you eliminated that. I checked some photos online and do see a similarity. Supposedly both tomatoes and potatoes get the same blight which wiped out the potato crop in Ireland at one point. I have never experienced this with my own potatoes but did have it in 2009 on the tomatoes. It spread fast and looked somewhat like your photos. Good luck - hope you get it identified soon. Am anxious to hear what it is too.
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Old July 5, 2018   #6
Eric02476
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Quote:
Originally Posted by Gardadore View Post
My first guess was Late Blight but you wrote that you eliminated that. I checked some photos online and do see a similarity.
The later stage photos do bear a modest resemblance, but several diseases look similar to one another once they've progressed that far. There hasn't been any Late Blight anywhere near my area reported yet by the state extension agency, and the weather has been hot and dry, so it's unlikely (I hope). Thanks for the good wishes.
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Old July 5, 2018   #7
KarenO
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I think it is a fungal disease called brown leaf spot.
Where did you get your seed potatoes?
Not sure whether it is possible for it to affect tomatoes, maybe research that.
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Old July 5, 2018   #8
Eric02476
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Quote:
Originally Posted by KarenO View Post
I think it is a fungal disease called brown leaf spot.
Where did you get your seed potatoes?
Thanks, Karen. That could be it, I'm continuing to research. My seed potatoes were certified from the Maine Potato Lady, a reputable operation, so that's unlikely (though not impossible) to be the source.
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Old July 5, 2018   #9
brownrexx
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If it were me I would send photos in an e-mail to Maine Potato Lady and ask if they have any ideas. They probably know more about potatoes than most people.
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Old July 5, 2018   #10
NathanP
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The easiest control would be to simply remove all foliage that appears to be infected and see if you can control or limit it's spread. Potatoes can lose up to 40% of their foliage will little impact on yield, depending on variety. So you could that and still have a reasonable harvest if you can control this.
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Old July 6, 2018   #11
Eric02476
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Quote:
Originally Posted by NathanP View Post
The easiest control would be to simply remove all foliage that appears to be infected and see if you can control or limit it's spread. Potatoes can lose up to 40% of their foliage will little impact on yield, depending on variety. So you could that and still have a reasonable harvest if you can control this.
I didn’t know that, thanks Nathan. Good idea. I think I’ll hit it with Biosafe spray (hydrogen peroxide + peroxyacetic acid) which is pretty good for temporarily knocking back fungal diseases and finishing off infected leaves, then get to trimming as you suggest. Since I didn’t stay ahead of disease, mitigation is indeed the goal. Interestingly, the potassium bicarbonate spray did noticeably slow it down over the last couple of days, so maybe there’s some hope.

Quote:
Originally Posted by brownrexx View Post
If it were me I would send photos in an e-mail to Maine Potato Lady and ask if they have any ideas. They probably know more about potatoes than most people.
Good idea. Will do.

Last edited by Eric02476; July 6, 2018 at 11:47 AM.
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Old July 6, 2018   #12
saltmarsh
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I suggest spraying with Horsetail tea (equestum arvanse).

To make a gallon of tea, use 6 fronds 30 inches long chopped into 1/2 inch pieces (I use a paper shear).

Place chopped fronds and 1 gallon of tap water in a stock pot and bring to a boil. Boil for 15 minutes and allow to cool. (I use 18 fronds and 3 gallons of water to make a larger batch which last me a year.)

When tea has cooled, strain and store in plastic bottles labeled for use. The tea is shelf stable and non-toxic, doesn't need refrigeration.

To use the tea:

As a preventative spray combine 1/2 cup of tea per gallon of water and spray leaves top and botton to point of runoff.

For an active infection combine 1 cup of tea per gallon of water and spray leaves top and bottom to point of runoff.

This tea may be combined with other teas and sprayed at the same time. Claud
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Old July 8, 2018   #13
Eric02476
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Update: I appear to have arrested or at least slowed down the disease with repeat applications of the BioSafe and GreenCure spray, so that does suggest it's a fungal disease. Hoping I will get a modest harvest if I can keep some foliage alive for another 2-3 weeks (these are early varieties, thankfully).
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