TOMATO GROWERS WHO HAD A BAD YEAR, home gardeners and farmers alike, wonder how to prevent a repeat of widespread disease that wiped out huge portions of the 2009 crop in the Northeast and Mid-Atlantic: Will late blight, caused by the fungus-like pathogen called Phytophthora infestans, strike again, and is there anything can we do to guard against that? While I wait to hear more from authorities like Cornell University, here’s what I know; what I did last fall, and what I will do at spring cleanup time to help myself. One advance clue: It focuses largely on a treasure hunt aimed at finding every last volunteer potato in the garden.
First, even if your tomatoes faltered or died, you may not have had late blight (I did not, to the best of my knowledge). An examination by a plant pathologist is the only way to be sure, but extensive late-blight photos at this Cornell link provided visual clues.
Instead, one of a number of fungal diseases, particularly in a wet year like 2009, may have infected your plants, and/or a bacterial infection may have been present—such as a speck, spot or canker—oh, and there are viruses, too. We’ve talked about them before here. There is no shortage of possibilities; every time I look at Cornell’s Vegetable MD Online site, I am amazed and humbled that we ever ripen a tomato.
Some surprising facts, and my intended tactics:
- Assuming this year’s last blight was the same strain normally seen, it can only overwinter on live plant tissues, not dead, in a cold zone like the Northeast, which would mean just one potential host: potato tubers overlooked during harvest. Dig and destroy (trash) all overwintered potatoes as they resprout.
- Volunteer tomatoes that sprout in the garden or compost can be the carrier of various other diseases (though not late blight). Always remove volunteer tomatoes as they appear, to prevent other tomato afflictions.
- Seed that was saved is not a potential transmitter of late blight, which cannot get inside a seed or survive on it outer surface. (Some other tomato diseases do taint seed.)
- Other fungal diseases are soil-borne and do overwinter even in a cold zone like mine. A three-year rotation sequence is the best control—not replanting the area with tomatoes and potatoes and their relatives for that time (though peppers and eggplant are less readily infected).
- Some such diseases (not late blight) can even contaminate cages and stakes and tools, which should be disinfected with a 1:9 bleach:water solution. First wipe or brush off any caked-on soil; soak the implements for 10 minutes.
- Resistant tomato varieties such as ‘Mountain Magic,’ ‘Plum Regal’ and ‘Legend’ can offer some protection from late blight, says the University of Massachusetts Extension on their great late-blight fact sheet. Investigate appropriate resistant varieties to offer some protection against other diseases; this chart of disease resistance by tomato variety may help. [Update 2013: The latest breeding centers on “triple resistance,” meaning to early blight, septoria and late blight. In cooperation with Cornell and North Carolina State, and trialed in fields including at High Mowing Organic Seeds, triple-resistant ‘Iron Lady,’ for instance, a mid-sized red slicer, is now being put to a test in home gardens.]
- Tomato grafting, as we have discussed—using a more vigorous rootstock to support less-robust growing heirlooms in particular—is another possible tactic, but not as easy as merely sowing seed.
- Cornell’s late-blight fact sheet answers many other questions about this disease; a great reference, should you wish to know more.
- At plant-shopping time, buy local (trucked-in seedlings sold at big-box stores were implicated in the spread of the 2009 late blight outbreak) and carefully check seedlings for any spots on stems or leaves. Even better, grow your own.
(Doodle up top by our beloved Andre Jordan, of course.)
Great information Margaret. We didn’t have late blight here, but there is always a possibility. Tomatoes drive a hard bargain for such sweet fruit.~~Dee
I’ve been checking the web and haven’t been able to find a retailer for either Mt. Magic or Plum Regal. Has anyone else located a source? I ordered Legend from Vermont Bean and Seed. After this winter, who knows what the summer will bring…
Just this mornin I talked with a colleague who suggested we tell our readers not to use saved seed from last year’s tomatoes that might have been infected with late blight. Do you think it’s a good idea to say something like “An examination by a plant pathologist is the only way to be sure” your tomato plants are blight free when most folks I know are gardening on a budget? I directed my readers to Cornell’s vegetable disease Web site last year in several articles I wrote about late blight. One plant pathologist I spoke with told me the only way we’ll know for sure what will happen is when the growing season is in full swing this year. I’m not completely sure I was able to find every single cherry tomato that dropped to the ground of my late blight infected plants. I don’t think I’ll be relying heavily on a good crop of tomatoes this year as I have in years past.
@TC: The head pathologist at Cornell and other such top-level resources clearly state (Cornell PDF link is in the post above) that Phytophthora infestans cannot get through the seed coat into the seed, nor survive on the dry outside of the seed, so I feel comfortable about their certainty. But..all this is ASSUMING it’s the same strain as they normally see in this Northern region; all bets off if it’s a new strain. All of these recommendations pertain to the Northeast.
Some other diseases can be transmitted through seedlings from the previous year, hence my advice (as I have always done myself, not just this year) to pull any volunteers as they emerge and destroy them.
As for where I wrote only a pathologist can say for sure, I am sorry to be unclear and confuse you; all I mean is that technically it’s the only sure diagnosis, of course. Obviously we don’t have regular free access to a lab as home gardeners, so all you can do in the real world is compare issues that crop up to the photos on these reliable reference sites and read up to be alerted to the symptoms. My assumption that I did not have late blight here last year was based on my own observations, not a lab test.
find your blog most interesting.great info!!!!
i have grown tomatoes for 40 years.had no serious problems until 2009.lost all my confidence!!!
hoping this year will be different.
your blog got me through the winter doldrum.
Welcome, Louis. What a nice message, thank you. Glad to encourage/help/entertain anytime. I feel the same way: 2009 was a confidence-shaker of a season, with all those Noah’s Ark rains. But we will do better this year. Onward! See you soon again I hope.
Hi Margaret, Thanks so much for the educational pep talk. Those Cornell photos confirm my assumptions about what devastated my tomatoes last year. Sadly, I grew all but a few from seed; the remaining few came from a small Hudson Valley chain–not a box store–so who knows where it came from? I just decided this year to take a break from the seed-starting and buy plants from a very local trusted grower. If something goes bad I don’t think I’ll be quite as heartbroken…!
Good tips! Thank you for the information. I think crop rotation is always a good idea for any vegetable.
Oh dear. So even if we had no trouble with diseases, the little volunteers must go? It will make me so sad (the volunteers are faring much better than the seedlings under lights in the house). But, I suppose what must be done, must be done!
Welcome, Jennie. I know, it’s upsetting…but various tomato maladies can be transmitted from these new volunteers (again, not late blight). Your call what to do — I force myself to uproot them, emphasis on force. I hate not letting every last thing come to fruition, but one must be tough to be a gardener. :)
Just saw Rodale’s article about the blight…2010. It is in MD, PA and Canada as I write.
very thorough info!
Thanks so much for this practical advance, Margaret. I’m sure I had blight last year, but I’m still not terribly experienced with food growing. My cherry tomatoes tasted horrible for the first time ever — really acidy, not at all sweet. Could that be related to blight?
You’ve inspired me to look for space to start my own seedlings this year!
Last season we tried 30 Iron ladies. We ordered from High Mowing and got 100% germination. All of them produced well with no problems. This year we will be starting around 150 from saved seed. We had very little blight problem here ( in our garden ) N.E. PA. I did put on one application of preemptive home made bordeaux mix after a sustained wet period but it was, I think, mostly unnecessary. This will be the fourth year for the “new” large raised bed garden. All crops will be rotated and a major infusion of compost will be double dug into all the beds.