White substance on lilac bush bark #337610 - Ask Extension

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White substance on lilac bush bark #337610

Asked June 29, 2016, 7:50 AM EDT

My parents lilac bush and now also there to holly bushes have a white substance on the bark of the Bush and leave seem to be dying. Is this a fungicide? Or is this some sort of insect pest? How do we treat it? Can the bushes be saved?

Berks County Pennsylvania

Expert Response

A white powdery substance on the top of the leaf and on the twigs is powdery mildew. Here is a link to a publication on powdery mildew in lilac. It is important to remove and bag or burn infected leaves and twigs. Those areas are generating spores and spreading the infection. Once the plant is infected, the pathogen overwinters in the roots and stems, so you will need to be vigilant in removing all infected tissue as it appears, and also plant debris. There are fungicides for powdery mildew that need to be sprayed on a schedule if you decide on a chemical repsonse.
Eileen East Replied June 29, 2016, 8:06 AM EDT
Thank you for your quick response. After looking at the link you provided on powdery mildew and the pictures that publication contained, I'm not certain that this is powdery mildew. I was at my parents house last night and looked at the Lilac bush and I did not see the white substance on the leaves. The white substance is all over the bark of the Bush almost as if someone has painted all of the branches White. Is this a different form of powdery mildew?
The Question Asker Replied June 29, 2016, 8:31 AM EDT
There are several other fungal diseases that it could be, but now is the time to take a sample to the local Penn State Extension and get the plant clinic to diagnose the problem. Try to take leaves, infected twig or branch bearing leaves, and even a bit of root if you can get at it. Here is a link to their website. I urge you to do this because some fungal infections are lethal and some are not. Penn State will give you a correct diagnosis and a treatment plan. While you're at it, I would pick up a soil testing kit from the extension and send in a soil sample from around the lilac to check for root rots. Good luck with this. Hunting pathogens is real detective work.
Eileen East Replied June 29, 2016, 9:16 AM EDT

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