How to rid soil of tomato blight?

My urban garden has been consistently productive for most of the last 20 years.  Gardening in the city means I have just one small area that has sufficient sun light. So I have ignored the rule of rotating my tomato crop and the tomatoes  get the sweet spot in the garden every year.  Well blight finally caught up to me. Last year I noticed a little spotting and leaf curl and when I came back from a 2 week vacation my tomatoes were  all but dead. I removed all the tomatoes from the garden and added 6 to 8 inches of wood chips in the fall. This year I planted as usual just moving the chips enough to plant and then replacing the chips without touching the plants.
You guest it, my blight problem is still a problem. I have been spraying a mix of baking soda water and a drop of dish soap on both the top and bottom of the leaves and the wood chips as well. All for nothing, again my tomatoes are all but dead.

Is there any way to rid the soil of the fungus so maybe next year I can grow some tomatoes?

From what I understand this will remain in your soil for 3 or 4 years. Dispose of diseased plants in plastic bags.

Buy tomato blight-resistant tomatoes and plant them in a different spot in your garden.

Maybe it would be wise to trim some trees to give more sunlight to your garden.

My understanding of the situation is similar to Anne's. Ridding soil of a specific fungus isn't easy, and it's impossible if you keep feeding it by continuously planting their food in the same spot, season after season.

Now you could opt for radical interventions. Some would suggest removing the problem soil, bringing in new, or shifting existing soil around. My feeling about this is that you'd probably end up with tomato blight everywhere.

I suppose one could consider solarizing the spot for a season. Black tarps, EPDM, or plastic garbage bags have been used in the past to great effect to cook soil underneath. I haven't had the chance to experiment, but the next time I have the chance, I want to try using something porous and breathable, like blackout curtains, to see if it would also work.

In an urban environment, this might actually be a valid option. You'd want to stick to tarps, but you could probably plant your tomatoes out in five gallon buckets or whatever you have and sit them on the corners and edges of the tarps, at generous regular spacing. I wouldn't overcrowd the buckets because you'd shade out the whole tarp, which would mean not achieving solarisation temperatures.

Incidentally, the recommended bake time for soils and composts exposed to or infected by Phytopthora infestans is 120 °F (49 C) for 30 minutes. If you used a thermal probe or compost thermometre placed in the soil to a depth of 12", you could check the temperature on hot days. Theoretically, should it exceed that temperature for that period of time, the soil should be sufficiently solarised.

Do I believe that would actually work? Honestly, I feel that some foamcore insulation would be required along the perimeter to trap that kind of heat. To do it properly, I'd add glass, or better yet, a cold frame, atop the tarps, and a tightly-pegged sheet of plastic greenhouse sheeting tented over that.

One option I would consider strongly is that of fungal slurry treatments. I think I would take a known aggressive culinary variety, like Oyster mushrooms, or maybe winecaps,  make water and mushroom slurries of them and inoculate piles of woodchips. When I saw some myceliation of the wood chip pile, I would spread the pile out over the bare infected soil and add more slurry. I would probably hold off on the application of actively aerated compost extract until I saw some establishment of the slurry fungi in the mulch and into the soil. The compost extract would then go to feed the fungi in their fight against Phytopthora infestans.

I would also grow it out. Decide what else you could grow there that you also eat and delight in, and put your tomatoes elsewhere. Maybe some earlier-ripening or smaller varieties in containers would do until you could use your tomato patch again. For my much better half and I, that would probably be something like butternut squash, but it might be a stand of Russian Mammoth sunflowers, or I might grow an asparagus guild heavy on tomato companions, including diverse alliums and marigolds. By the time the tomatoes return, it would be a polyculture with an active and aggressive fungal component in the soil layer ready to compete with the blight for resources, just waiting to welcome tomatoes back into the fold.

I don't see any viable method other than solarising it, checking temperatures with a thermometre or temperature probe, that would kill the pathogen, along with all soil life, and shorten the time you have to wait to grow tomatoes in that spot again. I would even consider hammering sheets of corrugated metal sideways into the soil, such that they act as heat exchangers. Hot metal fins extending down into infected soil, heated and kept from cooling to the air by a cold frame, or even a black tarp; that might effectively and evenly heat sterilise the soil.

Honestly? I would plant something else, even just cycling good green manures, and do the slurry thing as described. Planting something that generates a lot of biomass and root zone exudates that are food for the blight's microbial competition helps the soil to outcompete it. In the meantime, grow tomatoes in another spot, perhaps in containers somewhere, or planters, which might isolate plants and soil from the existant fungi you're having issues with.

But good luck. All tomato diseases are plagues of mythic proportions. I once crowded 39 tomato plants of different varieties into the sunniest, breeziest spot in all my garden, gave them all they needed, and got so pissed off when the neighbour's blight spread to my garden, I dug a 7'x17'x3' deep trench and built a hugelbeet out of it. That was one hell of an afternoon.

Good luck, and may you beat it, or change things around such that you can wait it out.

-CK

It might be useful to look up and see if yours is "early blight" (Alternaria solani or Alternaria tomatophila) or "late blight" (Phytophthora infestans). I have a lot of experience with late blight, because around here, every single tomato plant planted outside dies of this every year without fail. We just prefer that to be in November rather than June. BTW, late blight can come early in the season and I believe early blight can come late too. So don't let the names fool you. But we don't have early blight here, knock on wood, so maybe someone else can say something about that.

One way to tell if it's late blight is to take what you suspect is an infected leaf, and seal it up with a moist paper towel in a ziploc bag overnight. If the next day it has a white fuzzy mold under the leaf, it's late blight and you're in trouble. Late blight is a mildew/fungus and is really voracious, it's what caused the Irish potato famine in the 1800s (some strains also infect potatoes and other nightshades). Serious business. Get rid of it.

Anyway, if it is late blight, its spores need live host tissue to go on living. The spores will only live on tomato, potato or other solanaceae plant material, and some strains only infect tomato plant material, nothing else. Any fallen bits of an infected tomato or plant in a bed that are kept moist and protected and somehow survive the winter will reintroduce the fungus the next year.

Late blight spores reproduce in cool, wet/humid weather, so 10-20°C (50-68°F) and over 80% humidity. The spores can travel many kms/miles in this weather. I try not to touch my tomato plants when it's cool and humid as I could be spreading spores myself, and definitely don't remove suckers, stake or prune until the weather dries up or heats up a bit. The spores can't reproduce or travel at all on a normal or dry, warm/sunny day, so that's when I handle tomato plants.

If you've got late blight in your area, it's highly doubtful you'll ever get rid of it as anyone leaving any infected live material around in your whole area can reintroduce it next year, including you, unknowingly, so it's best to learn to live with it and establish good habits.

When you see the first sign of infection, those telltale brown spots after a good spell of cool, drizzly weather, you need to start hacking away fast, as soon as the temperature and humidity are OK. BTW, if you have a few days of cool, wet or humid weather you need to be watching your tomato plants like a hawk! Go every day and check the situation.

You don't want to let the blight go systemic, meaning get really into the "blood"/sap/whatever of the tomato plant, then your whole plant is a goner. So I usually clip out the leaf + maybe a thumb-length of the branch it's on. If the spot is big, I take the whole branch, figuring some of the blight may have gotten into the sap of that branch. I'm pretty brutal and hack away and get all of the spots that look like they could be blight. If you get blight on a stem, just amputate, tomato plants are weeds and most varieties will start putting out new shoots from weird places. If you have a healthy sucker, you might do well planting that and it will usually grow like dynamite.

I carefully keep all the plant waste I hack off in a pile or two, and then I meticulously gather up every little bit of it and dispose of it far, far away. If you can solarize and burn it on a hot dry day, better.

Careful with your gloves, they can spread spores around too. I wash and dry them well after I've been taking care of blighted leaves. Sometimes I dip my glove fingertips and clipper blades in fungicide (see below) between plants too when removing blighted parts.

To prevent late blight, the only thing that works pretty reliably is some copper-containing fungicide like copper sulfate or copper oxychloride or some weird-sounding name like that. Look for one that's accepted in organic agriculture. It's not really organic and it's too bad to have to do, but no one has found an effective organic remedy yet, that's why it's permitted in organic ag. Copper and fungicides in general are not good for the soil organisms. Dilute it to the strength permitted in organic and spray the plants all over every surface. Any surface that's not sprayed can host blight spores. Most people here spray the plants about 3 times in a season, usually early to mid. And be careful not to do it just before a rain, that will just wash it off into the soil.

Never use the copper compounds to "cure" blight -- they cannot do that, they only prevent spores from settling on a surface. Once the plant is infected, you need to hack.

In the end, I like my soil life a lot, so I rely more on hacking and rarely spray. And I experiment with everything I hear, like a homeopathic remedy a friend made for me, nettle tea, horsetail tea, etc. And a friend swears by the copper wire method, he puts a thin copper wire through the main stem of each plant. He says it works for him, others disagree. Experiment to your heart's content and let's hope that someday someone finds a real organic "cure" that works. I get good enough results with the way I do things. You have to watch really carefully though and move in really fast when you see trouble.

So back to your situation. I would yes, as Anne said, maybe trim those trees. Only plant tomatoes where they'll get lots of full sun. I would ditch those woodchips and not put any new ones back. They are generally great, they keep the soil and everything cool and moist, BUT, but if you've got late blight going, this is just the environment this mildew needs to grow and it can shelter bits of fallen tomatoes or leaves with the spores in them. And -- not a usual permaculture recommendation, but keep the soil below your tomato plants clean and dry. Do not mulch. Water them deep every few weeks on a dry/hot sunny day. Right now, I might carefully take off the top 2-3 centimeters of soil from anywhere you've had tomatoes and black bag it, solarize it and ditch it if you're not satisfied you've killed all the spores.

Spores can only live in the soil itself (as opposed to a little bit of tomato material that is in the soil) if there are "A" spores and "B" spores in your area. This is thankfully very rare. But if it happens, the spores can reproduce sexually and those spores can live for years in the soil itself. We don't have that here, but check that out maybe with your local ag extension, that's a big problem if you have it.

Keep on top of it and best of luck!

One option I would consider strongly is that of fungal slurry treatments. I think I would take a known aggressive culinary variety, like Oyster mushrooms, or maybe winecaps,  make water and mushroom slurries of them and inoculate piles of woodchips. When I saw some myceliation of the wood chip pile, I would spread the pile out over the bare infected soil and add more slurry. I would probably hold off on the application of actively aerated compost extract until I saw some establishment of the slurry fungi in the mulch and into the soil. The compost extract would then go to feed the fungi in their fight against Phytopthora infestans.

Hey Chris, I'm wondering if you are just speculating here or if you have reports of it working. I would love to find a phytophthora infestans-eating fungus. Here in Europe where it's a BIG problem in most "green" areas, there's been loads and loads of research going on for decades and no one has come up with anything convincing. But of course, no throwing in the towel, we'll only ever find a remedy by continuing to experiment.

Also wanted to underline what you said about promoting airflow around your plants (even though that fateful summer it wasn't enough for you). It's a very necessary good practice to keep the area near the ground free of branches and leaves (trim off the low branches on your plants), space your plants well, and trim out branches or leaves that are touching each other or could soon. But as you say, sometimes that isn't enough. I've found hacking away at the first sign to be what's really worked for me. Sometimes, I've hacked some plants practically back to a stick. And if it's mid-to-late season, guess what, you're not getting much or any production off that plant. <tears>

If the weather's hot, you can chill, but if it's cool and wet, you have to be on top of it waiting for a bit of better weather for your chance to hack. My philosophy from here in endemic blight-land.

Thank you all for taking the time to respond!

Buildings are the main culprit of casting shade.  I think my neighbors would frown upon the idea of me trimming there garage back.

I have looked into the copper based off the shelf treatment. I have to admit all the warnings on the labels made me wonder why on earth I would put it any where near some thing I want to eat.

As I said before I tried the baking soda solution with out any luck. I didn't mention that before I applied the solution I trimmed back any branch that had a hint of yellow. Not just the leaf but the whole branch back to the main stalk. I did my best to work from the bottom up and remove the infected branches with out touching healthy branches. Said branches went in a trash can and where disposed of. I did this dance about every 3 days for about 3 weeks. I grow my tomatoes against a 6 foot wire fence panel that I let them climb. They are over 6 feet tall but the poor things have no branches for the first 3 feet. They are all but dead now, and the few tomatoes on the vine the squirrel's have been taking before they even start to ripen.

So of all the suggestions given so far I think containers may be the best fit for me.  I plan on moving in a year or 2 so I just cant justify any major soil removal and most every thing besides the tomatoes seem to be doing very well.

I was thinking 5 gallon buckets placed in the same spot. Am I just asking for problems?  If the buckets are partially buried to help with retaining water and regulate temperature lets say one foot of bucket showing above the ground.

How high can fungus jump? :)

How high can fungus jump? :)

Ha, ha, yeah, that's a good one. Unfortunately it travels in the air and can blow in from the next county, so yeah, miles and miles. The stripping down the bottom parts thing is just to improve air circulation, especially near the ground, so any water droplets that ever get on the plant can evaporate as quickly as possible. I try to just keep a palm or two off the ground free of branches and keep things thinned out farther up. Water droplets are an open invitation to blight spores. That's why they advise when watering tomatoes to make sure not to get water on the leaves, just the base.

I wouldn't hack too much just for yellow, that could be a lot of things. But the brown spots after lots of cool damp weather, that's trouble.

And some years, like looks like happened to you this year, nothing is enough. Funny how unfair nature is, they blight just goes after your tomatoes (everyone's favorite in the garden, honestly) and everything else is thriving. Cool damp weather is good for a lot of plants! So we try to console ourselves with that.

Do look into those copper products for next year and maybe also experiement with some varieties that are billed as blight-resistant as Anne said. The ones I've tried haven't impressed me, but I suppose there's good innovation going on every year in that camp.

You container planting is a great one, maybe you can have clean soil there and move them strategically to chase the sun. Anchor them well in case you get strong winds and make sure the drainage is real good. Maybe next year's the charm, keep your sprits up and keep at it!

Hey Dave.

No magic bullet, I'm afraid. I just find that having other aggressive fungal species tends to limit or slow spread in the soil; I still get tomato blight, but it kills the plants in November, rather than July, meaning it's only my indeterminates that I have to worry about.

I am positive there's a fungal solution to both types of blight. I would imagine it's the type of thing that Paul Stamets at Fungi Perfecta might be looking into. In fact, it's my supposition that the reason there isn't a widely available fungal solution to many horticultural and agricultural problems is the influence of the chemical industry.

Realistically, if someone has the appropriate conditions early enough in the season to get their tomato patch cooking in excess of the blight kill threshold, I'd say bring on the black tarps. This might be easier with raised beds, though the exposure might cool them more quickly, and they might not get up to temperature if not sheltered.

-CK

Dave de Basque gives a good summary on the late blight problematic.
Here in Central Europe we are having a big problem this summer because there is hardly a day without rain and nights are cool, so all over Germany gardeners are ripping out their tomato plants.

If the weather is unfavorable, there is not much you can do to prevent phytophtora. Spraying with baking powder is just a tiny bit of prevention but it can only do so much. Choose a sheltered spot if possible (no direct rain), keep the soil healthy, have good airflow and watch out which of your varieties manages best.

Exchanging the soil  and bringing in new one is a huge work, cost intensive and waste of resources. Charles Dowiding even recommends putting the infected plant material on the compost. I am doing so myself and late blight does not occur where I use that compost or where infected plants stood.
The ovo-spores of phytophtora are tiny and occur basically everywhere. They germinate if conditions are right. There are other ovo-spores that parasite on the blight spores, so a good balanced soil and compost (and not a dead soil bought out of precaution!) help to maintain a healthy plant.

Apart from that, planting tomatoes here in Germany will always depend on luck.

Up here tomatoes cannot be grown outside, and traditionally no one grows what I would call maincrop potatoes either because by mid August the temperature at night is back down under 10C (tomorrow night the 4th august it's going to be 7C) and it rains all summer, July and August are the wettest months of the year. So if I want tomato plants that don't die to blight they have to be in a greenhouse, the greenhouse can be totally open it's keeping the plants dry that counts. even if they have blight spores all over them they won't succumb if they don't also get wet.