Organic Methods of Dealing with Late Blight on Tomatoes?

Southern NJ, United States(Zone 7a)

I am assuming that that's what I get each year. The plants start to dry up from the bottom and eventually stop producing. There's a dramatic difference between the long row of tripods that does get some water from the oscillating fan sprinkler and the long row that doesn't - the ones that get overhead water are much worse. So I know that contributes to it. But I'm wondering whether there's some way I can strengthen my plants so that they are more resistant to this. I rotate my veggies and use mulch, but I haven't fertilized or amended anything beyond what I normally do with compost in the spring.

Elmira, NY(Zone 6a)

The organic treatment I have read about is copper. It's really expensive. Also, copper is bad for people, so you have to be careful when you use it not to get it all over yourself. That said, I have decided to grow either just currant and cherry tomatoes or no tomatoes at all until late blight releases its hold a bit here. I'm surprised you got it down there this year. Wasn't a real dry?

Southern NJ, United States(Zone 7a)

From what I'm reading now, what I have isn't late blight, because there are some green areas at the tops of the plants. It's probably some sort of fungal disease; if so I've had it for years, because my plants seem to do this each summer. Jaune Flammée is doing well and so is Petit Moineau, a currant type. St. Pierre always outproduces anything else in my garden, and I may still get some fruit from that although it does have some affected areas lower down. Most of the rest are toast - all yellowed and dried up from the ground up.

Ivinghoe Beds, United Kingdom(Zone 8a)

I guess what you have, greenhouse-gal, is not blight. You'd know it at once. The tomato stems grow purple/brown with a bruised look and the fruit swells with brownish bubules. So a copper-based remedy like Bordeaux solution probably wouldn't help. I've found that foliar sprays of comfrey tea or kelp solution keep down most forms of tomato foliage disease. So, curiously, does an infusion of horsetail (Equisetum arvens).

Efland, NC(Zone 7a)

Howdy "Doc" Yeoman! Nice to see you posting again.

I'm in and out as time allows. And yes, I'll be over to your place as the "slow season" comes on, giving me more time (I hope!).

Best to you and yours,

Southern NJ, United States(Zone 7a)

John, thanks for the tip about the foliar sprays. I don't have access to comfrey but I can probably use a kelp solution. How often would you spray?

Denver, United States

Well, I respectfully disagree with John and with GG's 2nd diagnosis. It does indeed sound like blight to me. Visit Cornell University's "Late Blight on Tomato" photo gallery at : to see if that's what you have. A nifty new thing there is a link you can click to some photos of other tomato diseases often mistaken for late blight. Long Island/Southern New Jersey : pretty close by any standards, so this ought to help.

Regrettably, once you HAVE late blight, you HAVE it. You can't kill it on the plants that have it. Basically, you can take preventive measures, ranging from the simply physical to the extremely chemical (and, I'd consider copper sprays in an otherwise organic garden to be extremely chemical and better left to large-scale organic farming operations that are more concerned with conforming to industry standards/regulations than with providing "clean, organic" produce in the sense that most home gardeners would find acceptable). Even after blight arrives (although it most like was always there, or was there in your neighbour's garden), what is usually thought of as "controlling" the disease is really just action to PREVENT it from infecting nearby plants. Please see the scholarly quotes following.

"For home gardeners the only available fungicides that are effective against late blight are protectant materials, which means that they must be on the foliage before spores land on leaves and initiate infection. (Infection only occurs when the leaves are wet.) Therefore, continuous fungicide coverage is necessary to protect plants from infection. Tomatoes and potatoes are susceptible to late blight at any time during the growing season. Choose a fungicide that has maneb, mancozeb, chlorothalonil, or fixed copper as an active ingredient AND has tomato and potato late blight on the label. Of these fungicides, only some of the fixed copper products are approved for organic production." Cornell Univ

"Because late blight can overwinter on volunteer potato or tomato as well weedy solanaceous plants, it is imperative that volunteers and nightshades be controlled in organic production. Discovery of late blight nearby or within a planting would call for protective spray measures as well as removal and destruction of infected plants or plant parts. Application of fixed copper with an acceptable labeling for organic use can offer protection against the oomycete that causes late blight, however; copper accumu-lates in soil. See “Materials Allowed for Organic Disease Management” . The biocontrol material, Serenade, suppresses late blight and in rotation with copper resulted in marketable fruit even in the presence of active late blight pressure. Rotating out of solanaceous hosts for three years will help to avoid copper build-up as well as populations of other pathogens that affect tomato." OSU Extension [that's Oregon]

I've heard, but not tried, that nettle infusion, if sprayed on Solanaceae and Cucurbitaceae (as well as Viniferae) will prevent all sorts of fungal infections, including late blight. I've heard the same about horsetail and, in fact, in some places there seems to be a nettle vs horsetail enthusiasts competition in this regard, but I've yet to see any scientific studies. You would think they would exist, but I've not run across them. I have too many nettles and horsetail both in my yard, but since the horsetails are mostly in the raspberry patch and since the adjacent barren ground is about 20% nettles, nettles will win my approval simply from a practical point of view. A friend also tells me that nettle infusion (just like kelp infusion) is a good natural growth stimulator, especially for young seedlings and transplants, so maybe I'll try that next year!

In any case, do check out the Cornell site and let us know the verdict : late blight or something else.


Southern NJ, United States(Zone 7a)

PR, thanks for the information. I'm not at home right now (I'm in France, in fact) but as soon as I return I'll take a look at my plants if there's anything left of them, and then check that site. Now I'm wondering if it's septoria leaf spot.

Berne, IN

Excellent images on Late Blight, thanks for sharing. Has anyone tried Serenade Garden Disease Control for an organic preventative for LB?

Post a Reply to this Thread

Please or sign up to post.