Hi, it's possible it didn't go through since I sent it from my phone before and this time I used my laptop. But what can you tell me about my lilac bushes?

I have about 30 lilac bushes that all lost their leaves in early August. I submitted a question as to the possible cause a few weeks ago but had not heard back, wondering if you could help me with some information or advice.

Thank you for your question.

It can be difficult to diagnose a disease from photos only, but the pictures you provided are consistent with a leaf spot disease. There are two fairly common leaf spots on lilac: Psuedocercospora leaf spot caused by fungus and Pseudomonas spp Leaf Spot, a bacterial disease.

The high heat/humid weather in the Kalamazoo/Grand Rapids area July and August provided a perfect breeding ground for fungus. The only way to verify whether your lilacs are affected by the bacterial or fungal leaf blight is to have a sample tested by a lab. Information about the diagnostic services at the MSU lab is available at: https://www.canr.msu.edu/pestid/ There is also a site that addresses suggestions for choosing a sample to submit: https://www.canr.msu.edu/pestid/submit-samples/

Whether the leaf spot is bacterial or fungal, the main treatment is to remove infected leaves and debris from under the lilacs and trim out any dead branches. Decrease the density of the shrub so that sunlight reaches inside the shrub and allows it to dry out quickly. Do not plant lilacs closely to other shrubs, thus allowing airflow around them. Water from below and make sure the roots receive water during hot dry droughted periods.

It may be an artifact of the photos you sent but the lilac shrubs do look like they are pretty tightly spaced. The health of the lilacs may benefit from greater spacing distance.

Leaf blight is unsightly and may affect next year’s flower output, but it is rarely terminal. If you have the foliage tested and it is fungal, the application of a fungicide next spring from bud break until the damp spring weather ends can limit damage next summer. Repeat fungicide application every 14 days or according to label directions. Treatment now is not indicated since the damage was done in April and May.

Here are a couple of sites that address Lilac Leaf Blight:

https://hortnews.extension.iastate.edu/2021/08/summer-foliar-lilac-diseases

https://extension.illinois.edu/blogs/good-growing/2021-08-05-whats-wrong-my-lilac-summer-foliar-diseases-lilac

https://hortnews.extension.iastate.edu/lilac-pseudocercospora-leaf-spot

https://extension.umn.edu/yard-and-garden-news/lilac-issues-season

Thank you for your reply, I plan on trimming and opening up the lilacs on the inside. I planted these 18-19 years ago from suckers off of very old lilacs where I lived nest door. They were tiny sticks then and are now massive in size. Also I was out looking at them this afternoon (9/11) and noticed they have new buds, leaves and even flowers! In September!?! Have you ever heard of this?

Hello.

First, I wanted to add that I also found information on Septoria leaf spot.  Same look on the leaves, same conditions cause the fungus growth, same result on the plant, just a different fungus growing on the leaves.

Spring blooming shrubs can refoliate and rebloom in the fall.  The leaf buds and flower buds for next season (2023) are set shortly after bloom in the present year (2022).  When the plant is unusually stressed (like a leaf spot attack causing near total defoliation) it sends out hormones in an attempt to refoliate via the new leaf buds.  The same hormones that cause the leaf buds to break also affects the flower buds and causes them to mature.  So you are seeing next year's buds mature this year.

There is nothing you can do to "fix" this.  It is nature at work.  It may result in a smaller floral show next spring, but at the same time, it lets you know your lilacs are still alive!

Here is a site that explains a little more:

https://hortnews.extension.iastate.edu/faq/why-my-lilac-blooming-fall-instead-spring