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Tomato Pests & Diseases

Tomato - Early or Late Blight?

12 years ago

I've searched the web and the Gardenweb forums, but I'm still not sure what's going on with my tomatoes.

In the pictures linked below, the blotches appear shiny black, but it's because they're wet (we're having some light rain this morning). I brought them inside, and as they've dried, the blotches on the leaves have shiny brown patches near the middle, with black edges.

We've had crazy weather in northeast Vermont this year, with hot dry stretches, and warm to cool wet (VERY wet) stretches.

I grew them all from seed, and transplanted out just before memorial day. They've done quite well, and I have some green fruit on the early varieties.

I have just over 200 plants. I'm trying to decide if I can just prune the affected leaves and treat all the plants with a fungicide (organic), or if I need to cull all the affected plants.

Here is a link to the pictures: Click

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Comments (2)

lionheart_gw (USDA Zone 5A, Eastern NY)
12 years ago
It is neither early blight nor late blight.

Right now I would say that they have a bit of septoria. If I look closely at one or two of those photos, there are some signs of it. Also, there could be an issue with either over-watering or soggy soil that's not draining well. Of course, we can't do a lot about all this rain, *sigh*.

For the septoria, which doesn't look horrible right now, I would use a fungicide for vegetables - one that contains Chlorothalonil (Daconil, Ortho Garden). Use according to package directions.

All fungicides must be used as preventatives; none are curative. They will not kill existing disease but will keep it from starting and spreading. And, they must be applied regularly. If you are gardening organically, I would go with one of the copper-based fungicides.

Follow package directions for dilutions and frequency of application.

Now I'll let you in on a little secret here in the Northeast: :-)

Septoria is usually transient. Once the weather dries out and the temps increase, it will stop progressing. It is the cool, wet weather that creates the environment for it to thrive.

So, you don't normally get a fungicide just for septoria. However, a fungicide will help prevent early blight, which is very common and far more difficult to arrest. And, if there happens to be any late blight around, it will help to prevent that as well. So it's worth using to prevent other fungal diseases.

You can remove the affected leaves, but don't feel that you have to remove every leaf that has a small spot or two. As the septoria stops, it will just leave a few spots on an otherwise perfectly good leaf. However, if you're looking at cool temps and rain for another week, you may want to be more aggressive about removing affected leaves.

Some folks say that you should bag the affected foliage and throw it in the garbage to prevent the spread of disease. Do that, but don't think it will forever eliminate septoria and early blight. Those fungi are all over -- in the air, in rain droplets -- so you can be extremely fastidious and still get those fungus diseases. Just an FYI.

Happy gardening!
schmuckernuts
Original Author
12 years ago
Thanks Lionheart!

More cool wet weather this week . . . arrrrgh! Things might be improving by Saturday though.
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Thanks, here is the answer from my local extension. I guess it is all over our area after 2 weeks of rain: Your tomatoes (and most tomatoes on farms) have septoria leaf spot, a fungal disease that is a little more aggressive than early blight. Most fungal and bacterial diseases start on the lower leaves and work their way up the plant. If you have the option to pull a few plants with this disease and plant some from a local greenhouse, that may protect the rest of the planting. If the spots are on too many plants to pull them all, then you can at least slow it down by removing lower leaves. Without a commercial fungicide, it may still spread.
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