Late blight in May? Help!

16 years ago

After a very nice and toasty April (we were in the 70s and even 80s most of the time) we had two horrible cold and rainy weeks in May. We had a couple of nights in the 30s and most in the 40s with daytime temps no higher than 55-60. Now I'm afraid I've got late blight on a several of my huge heirlooms. Just the dark spots and drying on the leaves so far, none of that ugly white stuff yet. I removed the affected leaves. One Black Prince has a dark spot on the stem.

Do I have to kill them all? From what I understand, late blight spores are airborn and are present in the soil, it's the cold rainy weather that lets them spread and flourish. We are pretty much out of the woods weatherwise, sunny and 70 for the next two weeks. Won't that stop the disease? Or am I asking for trouble by keeping them?

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Comments (6)

digdirt2
16 years ago
Zone 4 and you are already planted out in the garden?? And they are already "huge"??

If so, then it is 10x more likely that you are dealing with cultural/environmental damage than LB. Air temps are irrelevant. What are your soil temps?

Dave
carolyn137
16 years ago
Have you gone online and looked at any disease sites to help confirm that you might have LB? I'd hate to see you kill your plants if what you're seeing is not LB.

There are some very early symptoms that are seen before even any leaf syptoms are seen and that's the bending down of the petioles.

So perhaps Googling Late Blight might help b'c I know I wouldn't make a Dx based on just some dark spots on the leaves. ( smile)

Carolyn
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grow_darnit
Original Author
16 years ago
Thank you! I am feeling better now.
Dave, I started them from seed back in February. They are not in the ground yet. They were getting big, so I repotted them in 3 gallon pots and they moved into a hoop house waiting for some better weather. (Before, when they lived in the house, I used to take them out every morning and bring them in the house every night so they could get sunshine). Now with rain pretty much every day and not a ray of sun for a week the temps in the hoop house slowly but surely almost leveled with the outside temps. We've been having colder weather for 2 weeks and mist or rain every day for a week. The plants in the hoop house have wet leaves from condensation pretty much 24 hours. So I got a little worried. I'll post a picture when I have a bit more time (after I feed the little one) for a better diagnosis. Thank you for your help!
grow_darnit
Original Author
16 years ago
Carolyn, I did Google it. Actually, at first I wasn't even sure what I've got, so I tried images of diseased leaves. I used this link for ID. Some of the milder cases there looked like what I saw on my plants. I didn't see any info on petiole bending though. Where can I find that?

Here is a link that might be useful: late blight
digdirt2
16 years ago
AHHH that's important info. Makes a big difference and much more sense now. But even with that info the odds are still 10:1 it is just environmental stresses.

Sounds like you need to increase the air circ in the hoop house to dry it out some. Even a fan would be a big help but some heat would help dry it out even better if that's possible.

Dave
grow_darnit
Original Author
16 years ago
Dave,
that's what I was thinking too. So I got a tiny space heater with a fan in there last night. I just looked at them and the leaves are all dry now! The Fire marshal stopped by too, so I gave him your coordinates ;) I separated the two main offenders just in case, but I believe you are right, it is probably environmental/cultural.
Oh, and I just looked again at the website I was using for ID and this time I READ THE CAPTIONS. "The brown spots on this tomato stem (below) are probably not due to late blight." D' OH!!! Can I start feeling stupid now?
Anyway, thank you guys, you took a load off my shoulders and saved two innocent tomato lives!
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