Recommendations for ridding one's soil of blight spores

anney(Georgia 8)July 26, 2009

The weather has really screwed up gardening for many this year where it was unseasonably cold and rainy. Since there is a plague of late blight for tomatoes and potatoes rumored to have been triggered by infected plants sold by big box stores in the northeast and exacerbated by the weather, many are having to destroy their plants in midseason this year. Late blight spreads rapidly with wind and wind-blown rain action. Early blight of tomatoes, a pretty common problem anyway and not as lethal to plants, has also become rampant, as have other plant or leaf diseases.

My tomato plants are all on their last leg, not from late blight (which hasn't moved South yet en masse) but from septoria/anthracnose and early blight, I'm sure triggered by the strange strange weather we've had. They're browning and dying as they usually do in late August/early September, despite my spraying with antifungals for the EB. I didn't ID the anthracnose until it was too late. Fortunately, my bell pepper plants are incredibly green, lush, and are producing enormous numbers of fruit. Go figure.

Therefore, I'm worried about the garden soil for next year. After I've removed all the tomato plants, debris, and mulch, I want to do some serious organic treatment of the soil to rid it of as many of the spores and bacterial infections as possible, and then pray that the weather rights itself next spring and the diseases don't show up again.

As I said, I'm worried about the soil. I have only a few ideas, maybe put the (I'm sure) spore-ridden mulch in a very hot compost pile or compost it separately for a couple of years, application of corn meal to the soil, work in lots of compost, and/or solarization of the beds. Then new mulch that's clean next spring.

Any other suggestions for accomplishing this feat?

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Your University of Georgia once had a very good article on soil solarization available on line but apparently the link has been changed.
People I correspond with all over the world have related how they have solved a plant disease problem by composting infected plant debris and then working that compost back into the garden soil, for years. But more than that what I am hearing from these people is that the key is to get enough organic matter in the soil, the soils pH in the proper range fro the plants being grown, and the nutrients well balanced.

Here is a link that might be useful: UG CES

    Bookmark   July 26, 2009 at 6:43AM
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anney(Georgia 8)


Since making the post above, I found some very interesting information about Late Blight. This site is focused (only) on Late Blight in potatoes, but it's the same Late Blight disease that infects tomatoes.

If your winter weather includes freezing, that may destroy the spores! I posted this link and information on the Tomato forum since so many people in the northeast are reporting Late Blight there, but it might be helpful here, too. If infected tubers freeze and die over winter..., the disease cycle is broken, and very often the disease does not appear even when the weather conditions are favorable.

Thus, your thought about "composting infected plant debris and then working that compost back into the garden soil" might be a good alternative for those whose winter weather does not include freezing. I'd sure make certain that the infection was totally destroyed, maybe by "cooking" it for a couple of years. I don't think that the soil is the original problem with blights though. Good soil can produce healthy plants that are still infected or destroyed by air- or water-borne blights or other diseases. Then the spores end up in the soil.

But, here's more information on Late Blight from the link. There are several "varieties" of LB. Late Blight is a "water mold", flourishing in wet conditions. Its damaging progression is often from the top of the plant down to the soil and roots, with water on the plant providing the conduit. Phytophthora infestans, the causal agent of late blight, is not a true fungus but a water mold belonging to the phylum Oomycetes. Oomycetes such as P. infestans form large, clear, lemon-shaped spores called sporangia on stalks called sporangiophores (Fig. 7). Though they are relatively large in comparison to those of true fungi, they cannot be seen without the aid of a microscope that can magnify at least 100 times. The sporangiophores have distinct periodic swellings at points where sporangia were produced.

Sporangia may germinate at temperatures between 44 and 55F when free water is present on leaves and form 8 to 12 motile zoospores per sporangium (Figs. 7, 8). These swim freely in water films, attach to the leaf surface (encyst) and infect the plant. Encysted zoospores infect leaves by penetrating the leaf surface with a germ tube, either through stomata (breathing pores) or by means of direct penetration (Fig. 8). At temperatures of 55 to 70°F, sporangia germinate by means of a single germ tube. Night temperatures of 50 to 60°F accompanied by light rain, fog or heavy dew and followed by days of 60 to 75°F with high relative humidity are ideal for late blight infection and development.

....Water-borne spores appear to follow stems and stolons in a water film into the soil, reach tubers and cause infection...

I wonder if freezing would kill Tomato Early Blight fungus spores that have drifted onto the soil. Can't assume it would though, since the diseases are entirely different.

    Bookmark   July 26, 2009 at 7:22AM
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anney(Georgia 8)

Well, it appears that Early Blight spores and the Alternaria pathogen are NOT killed by freezing. [The information is visible in a search but not in the research summaries given, so I can't post a link.]

So I suppose if these two diseases end up in the soil, they must be dealt with differently, as I suspected. For my situation (no Late Blight so far) that probably means solarization. Sigh.

    Bookmark   July 26, 2009 at 7:41AM
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anney(Georgia 8)

Check out this discussion on the tomato forum.

Back to square one.

    Bookmark   July 26, 2009 at 8:23AM
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My gardening experience confirms what "Kimmsr" said, in the post above. I compost all plant material from our yard, diseased or not. We will always see some sign of blight in the tomatos by the fall, so this material is going into the compost pile every year. Our compost pile always has some brush, small tree branches, raspberry canes, and sunflower stalks. We have no manure to feed the pile, it is mostly "browns." I don't think that it ever gets very hot. I dig up the finished compost, from the pit underneath, every spring. This material is spaded into the garden. This year we planted 6 tomatos. Three of these are in the garden plot, and they are free of blight. The other three are in new locations, where we haven't gardened, and I have not applied compost. One of these is showing sign of blight, and the other two are healthy.

    Bookmark   July 26, 2009 at 9:39AM
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Anney, you have noticed that here in the south commercial growers plant tomatoes in the early spring, harvest all by about July 4 and then pull the plants and sow a cover crop. This is due to the ever present fungus problems plus heat. The southern home gardener has the best chance of control over the situation by growing tomatoes in containers where the soil can be controlled and the plants mulched well. Coir can be purchased by the yard at good nurseries and I find it to be the best tomato mulch as it does not seem to encourage fungus spores. Plus, the southern gardener has to try growing different tomato varieties until finding those most resistant to whatever problems are present. Georgia is not WI or MI. It is it's own ecosystem and it takes a bit of experimenting to find the techniques and varieties suitable.

    Bookmark   July 26, 2009 at 3:53PM
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Before you wear yourself out trying to get rid of the spores think about it. There is no way to prevent the spores from becomeing airborne and infecting any spot that you have tried to remove them from. A car passing by that raises dust or an insect that flies from one spot to another can carry the spores. If that is not bad enough storms will pick up dust and then deposit the spores thousands of miles away.

The best you can do is try to prevent an explosion of spores. With weather being a big factor this year in every part of the country, look for things that you can do this year to limit the problem next.

    Bookmark   July 27, 2009 at 12:06AM
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anney(Georgia 8)


Blight spores in the soil are my concern, not the spores that are airborne. Blight spores in the soil guarantee your plants will be diseased, while you have a chance at protecting your plants against airborne disease.

    Bookmark   July 27, 2009 at 5:28AM
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Sir Albert Howard, while stationed in India as an Agriculture Agent, noticed some farms in the area he worked grew crops and animals that were disease free while other farms could not raise anything healthy and he looked into the whys of that and found that those farms with the healthy crops and animals followed practices that Sir Albert outlined in his "An Agricultural Testament" and "Soil and Health".
Apparently, today, we have a large number of people that have not read or understood what Sir Albert wrote and have a hard time undstanding that getting the soil into a good, healthy condition will help grow strong and healthy plants that are better able to withstand plant diseases and insect pests. Far too many people today are not familiar with Friend Sykes and that he took a farm that was sick and using the principles outlined by Sir Albert converted that farm into a healthy and profitable farm. Lady Eve Balfour did the same. J. I. Rodale read Sir Alberts books, believed, and founded Organic Gardening and Farming magazine to promote these ideas, and subjected himself to great disdain in doing so by people that either did not, or would not, understand the basic principles of organic gardening/farming that are not all that different than what the USDA was really telling farmers at that time.
If you are having a problem with plant diseases or insect pests, or both, you need to look at the soil you are growing these plants in to see what the problem is. It is as simple as that.

    Bookmark   July 27, 2009 at 6:44AM
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anney(Georgia 8)

No, kimmsr. How many times do people have to tell you? In the US, airborne diseases infect plants and then get into the soil via spore-shed. It has nothing to do with the health of the soil. After that the diseases infect the plants the next year if the diseases remain in the soil, no matter how healthy the soil was to begin with. Then the next year's plants are infected by the soil. Simply, we now live in a very polluted air-borne agricultural environment that in many cases overwhelms the natural health of plant and soil life, a degree of pollution that did not exist 40-50 years ago.

That said, there is this that supports your statement: It is worth remembering that the numbers of beneficial microorganisms far outweigh the plant pathogens. Beneficial microorganisms can live in a symbiotic relationship with plants, improving their fertility and disease resistance. Other microorganisms that live in the soil are predatory, and help to suppress plant diseases; this includes fungi that prey on nematodes. Most significant, though, is the cycling of organic material, within the soil, by the microorganisms, which cause decomposition. The organic gardener relies on this cycling to produce compost and build a healthy soil.

While great soil is what gardeners need, it does NOTHING to prevent airborne diseases from finding your healthy plants, nor does it prevent infection if the spores are in your soil have not had time to be consumed by the beneficial soil-dwelling micro-organisms. Furthermore, there are no plants that are truly resistant to plant diseases if the species itself is vulnerable to those diseases. More accurately, some varieties of plants are more tolerant of disease damage than others, even though they, too, become vectors for the spread of the disease through bacterial contagion or spore-shed.

The BIG question is how long it takes beneficial organisms in healthy soil to destroy pathogens. If winter soil where the spores are located freezes, there isn't going to be much micro-organism activity, and the diseases usually just lie dormant until the next spring. From all accounts it takes several years.

Crop rotation may be one of the solutions, as well as letting diseased soil lie fallow for 2-3 years. Growing in containers. The first two are often not options for home gardeners who don't have that much garden space, so in addition to providing for the healthiest possible soil, we must also look for ways to organically speed up the destruction of plant pathogens if we want to garden each year.

    Bookmark   July 27, 2009 at 7:49AM
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This was my first year to have a vegetable garden in my backyard (20' by 24'). I live in a subdivision that was previously a pecan orchard.

My tomatoes succumbed to early blight, anthracnose and tomato spotted wilt virus. I bagged and trashed all the plants along with the wheat straw mulch last weekend. I was afraid to compost the debris in case the diseases continued to live in my compost pile. I have to admit that I didn't spray with any fungicides or insecticides because I wasn't sure what to use. Needless to say I had every bug known to man in my garden, primarily stink bugs, leaf footed bugs, squash bugs and thrips.

I had purchased my tomato plants from one of the "big box" stores and a locally owned seed and feed store. The varieties were "Celebrity", "Roma" and "BHN 640", supposedly disease tolerant varieties. However, the tomatoes developed the virus and fungal diseases because they were already diseased when I purchased them or because of airborne or pest dispersion. I guess it doesn't matter how they got the diseases because now the diseases are in my soil.

I have already placed plastic on the soil where the tomatoes were grown. I'll leave that bed fallow until Spring and then add corn meal and compost. I'll rotate my crops. I plan to initiate a preventative fungicide spraying program (Daconil) when the tomato plants are still small and I'll initiate an insecticide spraying program (pyrithrin). I realize that this won't prevent any diseases, but at least it may "check" them. I'll spray the insecticide late in the evening (8:30 pm-9:00 pm)when the bees aren't buzzing around the plants. I know this isn't organic gardening, but I don't think it is possible to go completely organic when growing vegetables in south Georgia. The conditions here (long, hot, humid growing season) are just too favorable for pests and diseases.

    Bookmark   July 27, 2009 at 9:58AM
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Hi All, has anybody ever noticed that some people get dandruff and others do not? Or that sometimes you yourself get dandruff but not all the time? Could it be your Head & Shoulders or your diet? What is the active ingrediant in dandruff shampoo? Selenium. Dandruff is a fungus and selenium is an anti-fungal. Check Wikepedia.

It seems that the blights may be around for awhile. If that is true, then I decided to try something not published as a plant anti-fungal. Selenium. I even toyed with getting the shampoo out, but since I have colloidal selenium on hand I decided to try that instead.

My test subjects were cucs with powdery mildew. Usually I would use milk as a spray, but have found that trace selenium is found in milk. I mixed four oz. selenium to a gallon of water with two drops of soap and sprayed the cucs late evening. Next morning they looked better, by the end of the day greener. Ten days later they are making many more cucs. Since then I have mixed and sprayed everything else, beans, toms, taters, pepers, cabbages, ect. All look better and producing better.

There are those here that stress a good soil test over and over. They are right, but, my tests do not show selenium. My next test will include selenium ever if there is a premium charge. My best guess is not sufficient. After I get the test results I will share it here and together maybe we can come up with a plan to ammend the soil, or maybe not needed.

Anyway a spray with colloidal selenium has done wonders.

Disclaimer, please do not shoot the messenger, the intent is to offer something that worked for me and may be of help.
Best regards to all.

    Bookmark   July 27, 2009 at 11:55AM
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anney(Georgia 8)


Won't shoot the messenger! My concern about the use of selenium is its possible consumption by way of the vegetables on sprayed plants.

It is a teratogen which if consumed in great enough amounts by pregnant women has been shown to cause fetal damage. To be accurate, apparently it would take a lot of it to have any discernible teratogenic effect on humans, so I'm just saying...

    Bookmark   July 27, 2009 at 12:25PM
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One last feeble attempt! BTW, spraying tomatoes with milk will have no effect on tomato blights. So, you need not worry about that aspect of the discussion. If you are that concerned about milk and selenium then it might be best for you to cease consuming all milk products.

Words written above lead you in the right direction to growing tomatoes in the adverse conditions of Georgia and the deep south in general. You can frog around all you want solarizing soil trying to kill off spores. It isn't going to work. If it did the commercial growers, who do solarize the soil for nematodes, would be using the method to grow blight free tomatoes all summer. As has been stated, soil is a major part of the answer and this is handled by container growing where you have control over the soil situation. A container grown tomato, well mulched, takes no more space in the garden than one planted in the ground surrounded by a tomato cage of some type.

Some years blight will be more prevelant than other years. The wonderful part of southern tomato growing is that when this happens you can always have young 'starts' to plant in July for a fall crop. You can fight these ideas, but most southern home gardeners have generally adopted them as the best way to grow tomatoes and other tender veggies such as green peppers and basil.

    Bookmark   July 27, 2009 at 2:14PM
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anney(Georgia 8)


Your suggests are fine, but the University of California has this to say about solarization. It works best in the South: Solarization controls many important soilborne fungal and bacterial plant pathogens, including those that cause Verticillium wilt, Fusarium wilt, Phytophthora root rot, Southern blight, damping off, crown gall disease, tomato canker, potato scab, and many others. A few heat-tolerant fungi and bacteria are more difficult to control with solarization.

    Bookmark   July 27, 2009 at 2:28PM
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I correspond with people in New Zeland that had problems with both early and late blight of tomatoes, until they were able to make the soil in the garden into a good, healthy soil and have had no problem with the blights since. The same with people in Ireland, Germany, South Africa, Canada, Spain, Alabama, Georgia, and several places around the world. There are skeptics out there that simply cannot believe a simple idea that good, healthy soil, a basic tenet of organic gardening, will help grow plants that are better able to ward off plant diseases and insect pests and if you have these problems then you do not have good, healthy soil.

    Bookmark   July 28, 2009 at 7:55AM
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Hi All, thank you for the heads up on teratogens. The list is quite lenghthy. See the link below. Good information here, usually. Pa soils near always test very short in selenium according to the farmers in this county.
I have no doubt that a good healthy soil will prevent all plant diseases and difficulties. However, what remains a mistery here is what would a soil test look like for good healthy soil?
Would it be one that hits the numbers that the testing company suplies? They vary from company to company.
Further heavy rain can wash out many of the nutrients and minerals. So how can it be possible to completely and always be pestilent free?
I would like to know more and I think others here too.
Best regards to all.

    Bookmark   July 28, 2009 at 1:01PM
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jajm4(z5 w. mass, usa)

The weather here has been ridiculously cold and wet. We had rain EVERY DAY for weeks at a time, and not just a drizzle (2 1/2 inches overnight was not unusual). It felt more like October than June, and the locals are calling it the Massachusetts Monsoon.

My feeling is that tomatoes are not adapted to this kind of weather. We had 40 degrees at night and 60 during the day, with 100% humidity. Even the wild mushrooms were rotting, and they LIKE cool, wet, cloudy weather. People were getting Seasonal Affective Disorder in July.

Some years you just have to be realistic and not try to force something to grow that's not going to grow. I don't plant watermelon in January, either. And penguins don't thrive in the desert.

Soil DOES help plant health, even for airborne spores, because healthy soil will make a healthy, more resistant plant. And when airborne spores are the issue, what are you going to do, stop the wind from blowing? Your best defense is a robust plant. It's the same as when there's a bad flu going around and some people just don't catch it. And for plants, robust immunity comes from healthy soil.

It's finally warming up in Massachusetts, and we're only getting rain about half the time now instead of every day. Still, it's too late here to start new tomatoes. We have to be happy that the sky is blue again sometimes and that we can try again for tomatoes next year. It's not the end of the world.

    Bookmark   August 4, 2009 at 2:20PM
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anney(Georgia 8)

And for plants, robust immunity comes from healthy soil.

Unfortunately, there are no tomato varieties that are resistant to early or late blight -- there are a few that appear to be tolerant of them. Blight infections don't have anything to do with the soil OR healthy plants.

The final word now seems to be that late blight spores terrorizing the East are killed by freezing -- good news for thousands of farmers and home gardeners. OTOH, early blight spores live through freezing weather in the soil, good or bad, or debris, so that's another issue.

    Bookmark   August 4, 2009 at 3:50PM
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Here is something you might find interesting... My garden had plenty of early and late blight and septoria leaf spot. The following year I installed a hoop house over half of it and planted tomato plants inside and out (8 in/10 out). I sprayed/coated the outside plants several times (during wet periods) with a well known product used to control these diseases. The inside plants were treated only once (lower leaves only). Soil was the same inside and out (top quality and ammended-well with organic compost). The plants in the hoop made it all the way to freeze disease free! No blight at all inside. The outside plants, well, they were pretty much toast about 45 days earlier.

The hoop house makes it sooooo much easier to garden. Never had to worry about pruning wet foliage (as it was often wet outside from the morning dew and rainstorms).

The hoop house was not sealed off. It was about 50% open (no side or end walls). The plastic on top kept the direct rain off but there was some splashing along the sides. (I use leaf mulch to keep the soil from splashing up the stems).

I can go on-an-on about the benefits of the hoop house but perhaps best is the reduction in plant disease. (but gardening during thunderstorms is pretty cool too!) My overall production was up more than 50%. And I suspect that with the dry and sunny conditions inside the hoop structure this winter (off-season), the bacteria and molds won't stand a chance (but I will still rotate anyway).

One note, I trained my tomato plants to a rope attached to the top of the hoops. It grew vine-like plants vs. bushy plants you get on cages. It keeps the foliage drier and blight at bay. I am now less concerned about growing heirloom varieties.

I hope I didn't get off topic.

    Bookmark   December 6, 2010 at 4:13PM
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This will not work for everyone but for those who have an open area and can do so one can place dry leaves , twigs and small dry branches and burn that area over.This works well also to rid the soil of the fungus that attacks cucumbers.Do it a couple of weeks before planting and you will have a little potash also.When you stop laughing think about it. Happy Gardening. Johnny

    Bookmark   December 7, 2010 at 6:45PM
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wayne_5 zone 6a Central Indiana

Johnny's and Rupp both sell mustard cover crop seed that both adds organic matter, controls nematodes to some degree, and fumigates the soil.

    Bookmark   December 9, 2010 at 10:32PM
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For organically treating septoria, my suggestion would be:
1) remove all plant debris very thoroughly
2) drench the affected area with the strongest hydrogen peroxide you can get (3% won't cut it). Best done when the soil is dry.
3) Follow the next day by flaming the top 4" thoroughly with a weed torch.
4) rebuild the sterilized topsoil with disease-free composted organic matter or with purchased mycorrhizae & worms.

and then I'd assume that the moist air will carry the spores back, so milk spray, bordeaux mix or something else could be sprayed to prevent reinfection. but I live in a frost free area, so I have to act or just live with the fungal spores everywhere.

    Bookmark   December 11, 2010 at 3:07PM
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sunfrog, this BUMP is for you.

    Bookmark   April 3, 2011 at 1:59AM
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After two years of blight on my tomatos I decided to try something rdical. Useing a propane burner like that used to control weeds I torched the ground untill I could feel the heat through my shoes then turn the soil 8" deep and torched it again. I am sure I have killed everthing bad and good, I am not sure what to add back to the to brig it bak to life. Any ideas?

Thanks Steve

    Bookmark   April 8, 2012 at 10:38AM
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I would do 3 things:
1) drench the sterilized soil with compost tea;
2) add some dissolved sugars, for re-establishing healthy fungal associations, using diluted molasses;
3) find some healthy topsoil you know to be blight-free (maybe 1 gal for every 20 gallons of soil in the bed) and sprinkle this into the sterilized soil, turning to a depth of about 6 inches. This acts as an innoculant, re-introducing soil microbes to your bed. If you can't find any topsoil you are sure of, you might have to go the more expensive route of purchasing soil innoculants.

    Bookmark   April 9, 2012 at 3:15PM
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Late blight has 2 ways of propagating. It can over-winter in tubers that do not fully decompose in home compost. See the research:

    Bookmark   March 27, 2013 at 12:24PM
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greenleaf_organic(8, TX)

I believe in healthy soil rich in nutrients and organic matter. That is definitely priority one. Some of us start with much poorer soil than others. (Like the intensely sun baked hardpan clay soil around this area of South Texas.) I just keep dumping copious amounts of organic matter and mulching heavily yet the soil is so poor to start with and that sun is intense so the process takes time to build healthy soil. So for now I still need some help for early blight. I hope it is OK to drop brand names, I have no stake in the company. Plant Wash by Soil Menders is natural and quite effective in my experience for early blight. I also read a thread some time back extolling the virtues of homemade kvass diluted with water and sprayed on plants too. Perhaps that would be good to also soak into affected soil. It is cheap to make. Just search the forum to find the two threads by "Valerie Ru". I once had a blighted looking spot that was rotting away the trunk of my new avocado tree and nothing I tried would help until I sprayed diluted kvass on the spot. Problem solved. Of course I still persist in building the health of the soil.

    Bookmark   April 25, 2013 at 3:02AM
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