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.
- 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.)