Lilac Bacterial Blight Question - Ask Extension
Hello,
I believe that one of my lilacs may have Lilac Bacterial Blight (I have attached a few photos). I am quite dismayed because I have a collect...
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Lilac Bacterial Blight Question #871439
Asked June 03, 2024, 10:47 PM EDT
Hello,
I believe that one of my lilacs may have Lilac Bacterial Blight (I have attached a few photos). I am quite dismayed because I have a collection of 14 varieties of lilacs that I love. I do not want to see the blight spread. I read the article from OSU Extension services titled "How to recognize, treat, and avoid lilac bacterial blight." I have a some questions:
1) Almost all the foliage on the bush in question has small dark spots (blight I assume), so removing all infected parts would mean almost completely stripping the bush/cutting it far back. Will is survive this?
2) The weather is supposed to dry up and get warm soon. Is there any chance that this will naturally control the blight?
3) I saw in the article that a copper-based pesticide can be used in early spring. Is it too late to apply copper-based pesticide this year?
4) Is pulling this bush up and disposing of it the the best option to protect my other lilacs? So far I have not noticed similar spots on any of them.
Thank you so much for your time and help!
Benton County Oregon
Expert Response
The good news is your lilac does not appear to have lilac bacterial blight. The very graphic description of blight in the publication you mention is "they look as though someone has placed an open flame near them. Dark black streaks form on one side of young shoots. The flowers wilt and turn brown and unopened flower buds become blackened."
This does not at all resemble the black spots and other damage on the leaves of your lilac, and comparison with pictures of bacterial blight confirm they do not resemble it.
Most likely this is a fungal leaf spot, which can be caused by any of several fungi. This also commonly occurs in wet springs – in other words, it is common in Oregon!
Pruning and spacing the plants for good air circulation can help prevent infection - your lilac looks fine in that regard. Don't overhead water once the rain stops.
Fungicide sprays (including copper) can definitely help, but those are only effective as a preventative - it's too late this year. If you spray next spring before the infection starts, you may be able to stop it from recurring.
There would not be much point in removing all the spotted leaves now, but in the fall when they are dropping, make sure to clear them all away to reduce infection the next spring.
Even if you pulled up this lilac, there are probably already fungal spores around, so I would say keep an eye on the other lilacs, and perhaps spray the closest ones with fungicide next spring too.
This does not at all resemble the black spots and other damage on the leaves of your lilac, and comparison with pictures of bacterial blight confirm they do not resemble it.
Most likely this is a fungal leaf spot, which can be caused by any of several fungi. This also commonly occurs in wet springs – in other words, it is common in Oregon!
Pruning and spacing the plants for good air circulation can help prevent infection - your lilac looks fine in that regard. Don't overhead water once the rain stops.
Fungicide sprays (including copper) can definitely help, but those are only effective as a preventative - it's too late this year. If you spray next spring before the infection starts, you may be able to stop it from recurring.
There would not be much point in removing all the spotted leaves now, but in the fall when they are dropping, make sure to clear them all away to reduce infection the next spring.
Even if you pulled up this lilac, there are probably already fungal spores around, so I would say keep an eye on the other lilacs, and perhaps spray the closest ones with fungicide next spring too.
