Managing Late Blight Organically

Is probably impossible, but after losing all the tomatoes in New York, we’re trying to see if at least one of the Maine tomato patches ( 2 outdoors, one under plastic) can pull through and produce.

Organic management tools include:



Being There

Being Careful

Being Realistic

Being fond of cherry tomatoes

And perhaps most importantly, Being a procrastinator – at least in our case… If I’d done all the tomato grafting I’d planned to do, there wouldn’t have been any leftovers in the greenhouse.

 Tomato plants in the greenhouse have so far escaped the blight.

Tomato plants in the greenhouse have so far escaped the blight.

* The Fungicide is Serenade, approved for organic gardening and a fairly effective prophylactic as long as it’s applied frequently. Late blight can’t be cured, and if it’s well established it can’t be stopped. But if it hasn’t yet taken hold it can be held at bay by Bacillus subtilis, the “good” bacteria that is Serenade’s active ingredient.

Seven days is the recommended interval between sprays unless disease pressure is intense.  We were only waiting 4 or 5 when the rain was incessant. Complete coverage is the goal but I’ve been paying special attention to stems since they take longer to replace.

* The Fertilizer is mixed fish emulsion and liquid seaweed, alternating with half-strength commercial soluble 20 -20-20, to provide as much instant nourishment as the plants can use.

In a good year, tomato plants don’t need much feeding, but this has not been a good year. Cold and wet kept them small and weak with poorly developed root systems, ill-equipped to fight the blight organically. Being robust is a plant’s best defense no matter what your gardening style, and it’s especially important if you don’t want to use strong toxins.

* Being There is essential. I’m sure one of the reasons we lost the New York tomatoes is that we weren’t watching over them. Here in Maine I’m monitoring the plants several times a day, removing leaflets that show signs of blight before the lesions can spread (far) or produce (gazillions of) spores. In rainy weather, leaves that looked fine in the morning can show definite signs of distress by late afternoon.

Stems are another story; once they get black spots all the leaves above the spots will almost surely perish. It’s best to cut off the whole branch below the spot so the plant can spend its limited energy making new growth. Of course after a few rounds of this you may not have much plant left  – see Being Realistic, below.

Everything removed should be bagged at once, then deeply buried, sent to the landfill or burned as soon as possible. Don’t put it in the compost or on the ground in the deep woods.

Post Season Update: In the end it didn’t help – except in the greenhouse, where removing all infected material as soon as it appeared pretty much stopped the problem. But in the greenhouse there wasn’t much of a problem to start with. Henceforward I’ll be playing the percentages, trimming early if there’s not much damage, removing plants if early trimming doesn’t make a big, quick difference.

* Being Careful can minimize the inevitable spread of spores. Try to avoid working in the tomato patch when the leaves are wet or when there is a breeze. If you have multiple tomato locations, start your patrols in the least infected.

And when the diseased material is deep in the plant behind other, apparently healthy growth, try to cut back by degrees from the outside in, to minimize disturbance.

* Being Realistic can be painful, but it’s a big part of being a successful gardener, organic or conventional.

It is now mid-August. Before deciding to keep diddling in an attempt to have some tomatoes; look honestly at each plant’s size, general health and leaf cover as well as the number of blossoms and baby fruits.

Is it realistic to expect mature tomatoes from this thing before frost and if so, how many? In a lot of cases it’s going to make more sense to simply destroy the tomato and spend the saved gardening time caring for the crops that are doing well – or would be if they got a bit more attention – and planting fall salads, cooking greens and roots.

* Being Fond of Cherry Tomatoes may or may not make any difference. The fact that our cherries are generally doing better than the main crop plants might be just an accident of placement – I plant the cherries nearest the main paths for easy browsing.

But as a subset cherry tomato plants do seem to be stronger than others. Might be because they have more leaves in proportion to fruit, might be because they’re closer to the original species. And of course might only be true in our gardens.

* Procrastination isn’t really a virtue, even if it did give us some plants better protected from blight.

The most interesting thing it’s given us is the opportunity to test a (presumably) vulnerable heirloom alongside a (presumably) tougher hybrid. The leftovers were from a spring plan to graft ‘Lilian’s Yellow,’ a reputedly very fussy heirloom, onto the rootstock of ‘Big Beef,’ a sturdy hybrid if ever there was one.

The successfully grated plants in New York died. The bits and pieces in Maine languished for months in not big enough pots until the blight drama started.

Now they are in bigger pots. If they keep on being healthy for another week or so I’ll run strings to the greenhouse rafters and start having hopes.

Related Posts Plugin for WordPress, Blogger...

Add to Google


  • Ali Said,

    Thanks for this. I will be using Seranade prophylatically next year, and planting more Matt’s Wild Cherry which has been completely untouched by Late Blight, Septoria Leaf Blight, or any other fungusy thing. Sigh. Good luck with the tomatoes! I am dying for some right now….

  • Leslie Said,

    Hi Ali,

    Thanks for the tip about Matt’s Wild Cherry – another vote for cherry tomatoes. Not something I think of as suitable for preserving, but this year…

    And last night Emma ( more about her soon) made a very nice simple pasta dish: rigatoni with a ton of cherry tomatoes that had been halved and briefly sauteed in olive oil with lots of garlic. So I guess we can work on thinking up more of those, and maybe this’ll be a year for Tomato Figs – candied; they’re better than they sound although not exactly versatile.

    As for the prophylactic Serenade, I’m not waiting until next year – too many other fungusy things still likely to hit the cucurbits, beans, zinnias etc., and B. subtilis is listed for a great many of them. Each time I make up a batch for the tomatoes I make it big enough to cover just about everything.

  • Ken Greene Said,

    Well put. I’d like to also add “A Sense of Humor” to the list. It’s helped us get through the depression of losing the bulk of our heirloom tomato seed crop.

    • Leslie Said,

      Hi Ken
      welcome! It’s a treat to have a comment from you. Agree completely about the sense of humor — gallows humor though it must be.

  • Paul Said,

    Ditto what Ali said. I had about 50 tomato plants. Now I have 5. All are Matt’s Wild Cherry. They were surrounded by late blight and didn’t get it. I did see it on some of the early fruits (which crossed paths with a lot of the live fungus). The plants however, were untouched and are now bearing beautiful fruits.

    I emailed this info to High Mowing, whom I bought the original seed from.

  • Patrick Said,

    Ms. Land,

    I have only just recently begun to read thegreengrower and your written contributions. I have always considered myself a pretty good gardener in the very challenging Dallas, Texas area,… learning from experience mostly over 30+ years observation and experimentation. However, I have a problem I am unable to figure out.

    Perhaps as many as 10 years ago I made huge garden areas in front of my house and mixed heavy material such as bags of mulches and oak leaves in an effort to improve (break-up) our black clay soil. My thought was by adding my idea of “organic” material there would be better nutrient and/or water availability as it decomposed. I had planted ground hugging Blue carpet juniper and Indian Hawthorn as main plantings.

    After initial success (about two years) the junipers began huge die offs. As they were removed, I noticed fuzzy white looking areas on the root systems and widespread in the soil. The Hawthorn, since I got them as healthy 1-gallon specimens, have never grown full and healthy looking. Their leaves start out very green after the spring bloom, then the year-old growth gets spots yellow and brown, with the affected leaves falling off soon after losing all the green.

    This reoccurring yearly process leaves very leggy and unhealthy looking plants, that after 10 years, have never grown larger than two feet in spindly diameter. Furthermore, I can not seem to get anything to flourish in my garden (more like bare black desert waste land). A couple of Nana Nandina and Jap Yew are holding up O K in exception. Amounts of water, small or large, is of no apparent help …

    Do you have ANY idea what is happening? Mold, Fungus, Disease, Bugs, Bacterium??? Do you have any ideas of specific products I could use to improve the possible situation, remaining plants or soil and where I could purchase it? Do I need to start over, sterilize the soil? I originally thought both of these type of shrubs were strong evergreens as I see them used in commercial settings, they can get huge. I could use some help if you can, please! Preferably not too expensive!

    Thank you in advance,
    Frustrated in Dallas, Patrick

    • Leslie Said,

      Hi Patrick

      Wow, when you say frustration you aren’t kidding!

      Here are a couple of thoughts:

      Both of your problem plants are susceptible to diseases that flourish where drainage is poor: Entomosporium leaf spot in the case of the hawthorn and phytopthera root rot for the junipers (although they may have something else, the white filaments are no doubt fungus but not typical of phytopthera; I’m thinkin’ they may be something that was breaking down the oak leaves).

      Which leads me to wonder if you chopped them up finely enough. Whole oak leaves can mat together and more or less turn into leather that takes forever to rot.

      And that leads me to wonder whether the organic matter ever got a chance to break down into a useful soil amendment. If your soil has no air in it, all that material would just sit there.

      If I were you, I would start over, possibly with raised beds/berms of higher quality soil. Compost the next batch of organic materials, then use the result as a thick mulch. Most plant feeder roots are in the top 8 inches or so of soil, so digging in the goodies actually puts them out of reach.

      Sterilizing the soil probably won’t help, but choosing resistant varieties of hawthorn might well put you on the path to success. There’s a good list, from Alabama’s Auburn university, here.

      Good luck!

  • Abbe Said,

    I am wondering how I should manage the planters after I have had affected tomato plants. I have both terra cotta pots and those upside down planters, which actually produced more tomatoes. I know that LB is waterborne, but I don’t know how to sterilize my two planter types. I don’t like bleach as it is terrible for the environment. Any thoughts?

    • Leslie Said,

      Hi Abbe

      Good Question! Fortunately, LB has only 2 ways of surviving for any length of time: on living solanceous plant tissue and in the soil. At least for now, the soil type is less common and has never been found in in the northeast. But no matter where you are you’re probably going to be fine, because both of those survival matrices contain moisture. As long as you let your planters dry out and remain dry over the winter you should be fine. Of course, adding some time in the bright sun would also be good – ultraviolet light and heat are both enemies of LB.

Get a Trackback link

Leave a Comment