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Late blight warning: Don’t can those tomatoes! August 19, 2009

Posted by ourfriendben in gardening, homesteading, wit and wisdom.
Tags: , , , ,

Silence Dogood here. It’s bad enough to be living in Pennsylvania in the midst of a late blight epidemic, which is wreaking havoc with tomato crops across the Northeast this year thanks to a cool, wet spring and summer that’s encouraged the spread of this destructive fungal disease. But today’s local paper carried a front-page warning that was so serious I felt I needed to share it with you all right away. Food specialists are telling people not to can tomatoes from plants infected with late blight. Some say you shouldn’t even eat them fresh. Yikes!!!

It’s apparently fine to eat a tomato from a blight-infected plant as long as the tomato shows no signs of blight (typically first manifested on fruit as brown spots near the stem end, which subsequently spread over the fruit). According to one expert, Margaret McGrath, a plant pathologist at Cornell University, you can choose to cut away blighted parts of infected tomatoes and eat the unmarked flesh fresh, but, she points out, even that part will have an off-flavor. Luke LaBorde, a Penn State professor of food science, doesn’t think you should eat blight-infected tomatoes at all.

Both LaBorde and McGrath are adamant that you shouldn’t can or freeze tomatoes from blighted plants. That’s because fighting the infection lowers the fruits’ pH and increases the risk of botulism developing after processing.

It’s not worth risking death or paralysis to can these tomatoes, folks. I’d advise simply cutting your losses: Don’t eat them, don’t compost them (which could spread the disease in your garden next year), just put a plastic garbage bag over each infected plant, cut the plant off at the base, seal the bag, and toss it in the trash. That’s apparently the best way to contain the fungal spores that spread late blight.

In case you’re not sure if your plants have late blight, here’s what to look for. I quote: “large, circular to irregular greasy grayish areas [on the tomato leaves]. Humidity may cause a whitish mold on the undersurface of the leaves. Late blight on fruit results in extensive superficial brownish areas.”

After reading this, I think I’ll skip my typical summer tomato canning this year just to be safe. Thank goodness I still have home-canned tomato sauce and salsas from last year!

          ‘Til next time,



1. Curmudgeon - August 19, 2009

Yikes! This sounds terrible! I’m sorry you won’t get to eat your tomato harvest! Are you doing potatoes or eggplants and if so are they affected also?

Actually, we’ve been eating tomatoes, especially tons of (blight-free) cherry tomatoes, so it hasn’t been a total disaster. It’s just that when somebody mentions botulism I get a little nervous. My understanding is that eggplants and peppers don’t get blight, despite being nightshades, but potatoes can. Thank God ours haven’t!

2. Laurel - August 19, 2009

Thanks for posting this! I have circulated this with the local food group I am in.

Thanks, Laurel! I think it’s important to get the message out.

3. Daphne Gould - August 19, 2009

Actually I swear that two of my eggplants has blight (Lavender Touch, my Slim Jims show no sign). Sigh. I really can’t see why freezing would be affected at all. You can’t get botulism from frozen food. So as long as the blight isn’t on the tomato itself, and the tomato taste fine, I would think it would be fine to freeze. I could see why it would be a problem if the tomato’s pH is higher in canning, but not freezing.

I just bought a pile of tomatoes from the local farm. Now I wonder if I should be canning them or not. I haven’t a clue if those plants have blight or not. I bought them to make salsa. My tomatoes are mostly orange and yellow and hence low acid anyway, so I didn’t want to use them to can. Maybe I’ll freeze the salsa this year. I guess if I do I won’t have to worry about following the recipe to make sure it is acidic enough. I can put in as little vinegar as I like. Hmm and I can put in more cilantro so I guess it isn’t all a loss.

Good point about freezing, Daphne. And if your farm-bought tomatoes show no sign of blight, you can them right away, and you perhaps add an extra dash of lemon juice or vinegar (or wine) to up the acidity, I’d think you’d be fine, too. Ack about the eggplant, though!

4. Jen - August 20, 2009

If you’re cooking them and using them for sauce, would that kill the botulism too? My friend has a huge canning project going on and I do believe she lost a bunch of plants to blight.

I wouldn’t dare answer that one, Jen, not being a food scientist. Maybe she should contact Cornell’s Extension Service and see what they have to say! Your friend shouldn’t have to worry about botulism in a fresh sauce, but canned? Gulp.

5. Daphne Gould - August 20, 2009

Jen no cooking doesn’t kill botulism. You need temperatures of 240F degrees to kill it off so you need a pressure canner to get to those temps or you need acidic food. Botulism won’t grow in food below a pH of 4.6. Tomatoes are canned with either citric acid, lemon juice or vinegar because not all tomatoes make the 4.6 cutoff. If late blight makes them even less acidic it would be hard to tell how much of an acidifier to use. I’d really love to see some pH numbers from plants that had blight and the same plants that didn’t. Did the professors have any hard data?

Hi Daphne! Thanks for the clarification. I don’t recall the article giving an exact pH for blight-infected tomatoes, but it would be great to hear what Professor LaBorde had to say on this!

6. Lzyjo - August 20, 2009

Aaaah! I am becoming more and more terrified of late blight!! I had no idea blight attacked the fruits as well. My tomatoes have something, which a lot of local plants have. I’ve looked at various pictures, but it doesn’t really resemble any of them exactly, it’s not good though, but the plants are still kicking!

Gack, I know what you mean, Lzyjo! I feel quite paranoid myself at this point. Yikes!!!

7. linda - August 21, 2009

Yikes is right! I’m glad you posted this. Our tomatoes are healthy as can be – no sign of blight. Maybe there are advantages having no neighbors with vegetable gardens, plants all started from seed, plus a brand new raised bed that they’re planted in. Still, It’s good information to share with gardening friends and keep in mind for the future, both of which I’ll be doing. Thanks for the info Silence!

My pleasure Linda! It’s a scary season, but sounds like you did everything right!

8. Becca - August 22, 2009

Silence, may I possibly reprint this on littlegreenbees–with credit and a link back? I’m not sure if we’re having this issue along the Gulf Coast but it’s really great info.

Feel free, Becca! I think it’s important to let people know.

9. Late Blight Warning–courtesy of Silence! « Little Green Bees - August 22, 2009

[…] Late Blight Warning Silence Dogood here. It’s bad enough to be living in Pennsylvania in the midst of a late blight epidemic, which is wreaking havoc with tomato crops across the Northeast this year thanks to a cool, wet spring and summer that’s encouraged the spread of this destructive fungal disease. But today’s local paper carried a front-page warning that was so serious I felt I needed to share it with you all right away. Food specialists are telling people not to can tomatoes from plants infected with late blight. Some say you shouldn’t even eat them fresh. Yikes!!! […]

10. Barrett - August 26, 2009

my toamatoes have blite and i was wondering if there was a way to can and how do u do it if there is

Don’t try it, Barrett! It’s not worth the risk of botulism. Instead, enjoy the unaffected tomatoes in salsas, sauces, salads, and sandwiches. If you want to can some tomatoes this year, look for bargains in bulk at your local farmers’ market and can those (as long as they show no signs of blight). We’re all hoping for better luck next year!

11. MsKanner - September 5, 2009

I can them from blighted vines as long as the tomatoes themselves are fine. Light blemishes are removed. Since I cut them in quarters to go through the mill faster, I see anything inside that doesn’t look right. I’ve never had a problem with off flavors. They’re pressure canned for 15 minutes at 10 lbs of pressure. They’re canned as sauce. I add citric acid. Not likely botulism would survive the pressure canning process.

Thanks, MsKanner! Pressure canning is definitely a safer way to go!

12. Nancy - September 8, 2009

I just bought 3-bushel of tomatoes from a farmer. About 30% of them have the bacterial blight spots on them. The onese that have no spots at all on them I have washed and seperated….and thrown all the spotted ones out. I do not have a pressure cooker canner. The canner I use is a boiling water bath canner. The sealed jars remain submerged in boiling water for 30-minutes. I add the lemon juice to my juice, and both lemon juice and vinegar to the salsa. Since I dont know if the good tomatoes came from a plant with blight, is it still ok to can my juice and salsa with the Water bath canner?

I wouldn’t do it, Nancy, not this year. I’m not, anyway. But you might want to call your local Extension Service and see what they have to say. Another option is to have a friend with a pressure canner can your juice and salsa in exchange for some jars. Or you could try freezing them this year (that should work fine for juice, but I don’t know about salsa—you might have to cook it down a bit or drain off excess liquid before using it). I tried to find a helpline at the Ball Company, creators of the canning bible The Ball Blue Book, for you, but was unsuccessful. I did note that if you Google “canning safety” quite a few sites pop up, but given this new situation, I’m not sure they’d address it. I think calling Extension is probably your best bet. Good luck!!!

13. Kendra - September 16, 2009

My tomato plants are just starting to succumb to late blight. I have pulled all of the green tomatoes and thrown out any that show any signs of rot or infection and plan to pickle the rest. I don’t own a pressure canner. Will the vinegar (5 cups for a recipe that yields 5 quarts of pickles) provide enough acidity to keep them safe?

Hi Kendra, thanks for checking in! I wish I knew an answer for you, but not being a food scientist, I don’t. I’d think your pickles would be safe, but that’s just a guess. To be sure, you should contact your state’s Extension Service and ask them. I wonder if you could turn green tomatoes into yummy refrigerator pickles the way I pickle cukes? As I understand it, those would be safe. Whatever you do, good luck!

14. Junkman (Chris, aka Dad) - September 16, 2009

Wouldn’t cooking, after the canning process, such as: I open a jar I canned, and use those tomatoes to start cooking up some sauce, salsa, etc. ? How would ANY spoors or fungus survive being cooked? Not just the heat from canning, but (also) the subsequent cooking to USE the tomatoes? That would be TWO times the tomatoes would be heated. I DO have a pressure cooker, and I use 15 pounds pressure. (That’s what my ‘jiggler’ is set for)
I would then later on use the tomatoes to cook up some spaghetti sauce, salsa, etc. so that’s a separate heating. I just can’t see how ANY mold or fungus could survive that and make me sick? As for botulism, it’s REAL easy to know if your canned tomatoes are going bad with it. Of course, NO one would eat that, as it looks and smells terrible! The lids will swell up from gasses produced, CO2, I believe, and you know right away if it’s bad, just from looking. If stored a couple of months or so, if they are going to go bad, they will have done so. Once sealed, nothing else is going to be entering the jars, nor leaving, either. It’s a sealed environment, and everything in there is staying there. Good or bad. It isn’t going to change, which is the entire point of canning to begin with, right? Once you have given the jars enough time to let any germs grow, if there are any, and none DO, you’re good to go. Two months time should be enough, but four absolutely should reveal any bad jars. Am I right, or do y’all think I’m off my nut?

I really don’t know, Chris. I think pressure canning would be a lot safer than water-bath canning, but as I understand it, unlike ordinary mold, you can’t tell if something has botulism by looking at it, which is why it’s so deadly. Obviously, as in any canning, if a seal pops because of air buildup or mold, you should toss that jar ASAP! But beyond that, I’d suggest contacting your state’s Extension Service and asking their opinion before forging ahead. Good luck!

15. kuu - September 23, 2009

can you use it for soup? blight tomato?

I’d think so, kuu, as long as you cut out any bad parts and ate the soup right away.

16. Newbie - October 8, 2009

I picked hundreds of green cherry and grape tomatoes when I discovered the late blight. Anybody have any good recipes for the ones that don’t show signs of blight? Should I wash all of the green tomatoes immediately or will that contaminate the tomatoes that aren’t affected?

Hey Newbie! Search our blog for a post called “Green tomatoes Penna. Dutch style” for recipe suggestions and a link to another blog with green tomato recipes. I’ll bet you could use your cherry and grape tomatoes in these recipes just as well as larger tomatoes if you halve them. If your tomatoes are clean and dry, I wouldn’t wash them until I was ready to use them. Good luck with your harvest! And don’t forget that you can substitute your green tomatoes for tomatillos in a fresh green salsa. Yum!

17. Mary Petersen - September 19, 2010

What if the fruit isn’t affected, just the vine?

Hi Mary! If your vines are showing signs of blight now and the fruit isn’t infected, I think that’s actually normal for tomatoes—that many tomato plants get blight at the end of the season, and you can put up your tomatoes in the way(s) you usually do and/or eat them fresh. But it might be worth a quick call to your state’s Extension Service just to check. Good luck and good harvest!

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