Lilac bush - Ask Extension
These brown spots are on a lilac bush – can’t see any pest. How can it be treated for a healthier bush?
Knowledgebase
Lilac bush #137011
Asked June 26, 2013, 2:10 PM EDT
These brown spots are on a lilac bush – can’t see any pest. How can it be treated for a healthier bush?
County Michigan
Expert Response
There are probably six different fungi that can cause leaf spotting on lilacs. But with all fungal diseases, you can prevent them but not cure them. The first step for you is to determine if you are still having a problem. Leaf spots do not have to damage the plant.
Think about when the leaf spotting was first noticed.
Are there more spots developing on the leaves that currently have spots? Or are the spots getting bigger? This may be something that is not active so it causes no more problems.
Are there spots on the newest leaves? That indicates that the problem is still active.
Are there dead shoots or is this just spotted leaves? Dead shoots are more serious.
How much of the lilac has spots? Are leaves falling off?
Leaf spotting that is not active may be unattractive but it does not have to be harmful. Do not pull off the spotted leaves. The green parts are still making chlorophyll for the bush.
If the disease is not getting any worse, just pick up and destroy leaves after they fall off at the end of the year. It could help prevent problems if the next spring is damp. If the disease is active and you believe the lilac is at risk, you can send some leaves to the MSU Diagnostic Clinic. You can find out about the cost and download forms by going to: http://www.pestid.msu.edu You can mail samples to them.
I don't know what you mean by "a healthier bush." Is it just concern over the leaf spots or is the lilac looking bad? General things for liliacs: they require at least eight hours of direct sun to bloom well. They should be mulched with three inches of wood chips to keep soil temperatures cooler, supress weeds and prevent top evaporation. The bush should receive one inch of water a week if it is not raining. Buy a cheapo rain gauge.
The soil pH should be around 6.0. You can get a soil test by purchasing a soil test self-mailer at www.msusoiltest.com and following the link to the MSU Bookstore. You will get a recommendation on how to fertilize it. Just do not fertilize in July or August. It is too hot and you do not want to push any new growth late in the season that could be killed in a harsh winter.
Think about when the leaf spotting was first noticed.
Are there more spots developing on the leaves that currently have spots? Or are the spots getting bigger? This may be something that is not active so it causes no more problems.
Are there spots on the newest leaves? That indicates that the problem is still active.
Are there dead shoots or is this just spotted leaves? Dead shoots are more serious.
How much of the lilac has spots? Are leaves falling off?
Leaf spotting that is not active may be unattractive but it does not have to be harmful. Do not pull off the spotted leaves. The green parts are still making chlorophyll for the bush.
If the disease is not getting any worse, just pick up and destroy leaves after they fall off at the end of the year. It could help prevent problems if the next spring is damp. If the disease is active and you believe the lilac is at risk, you can send some leaves to the MSU Diagnostic Clinic. You can find out about the cost and download forms by going to: http://www.pestid.msu.edu You can mail samples to them.
I don't know what you mean by "a healthier bush." Is it just concern over the leaf spots or is the lilac looking bad? General things for liliacs: they require at least eight hours of direct sun to bloom well. They should be mulched with three inches of wood chips to keep soil temperatures cooler, supress weeds and prevent top evaporation. The bush should receive one inch of water a week if it is not raining. Buy a cheapo rain gauge.
The soil pH should be around 6.0. You can get a soil test by purchasing a soil test self-mailer at www.msusoiltest.com and following the link to the MSU Bookstore. You will get a recommendation on how to fertilize it. Just do not fertilize in July or August. It is too hot and you do not want to push any new growth late in the season that could be killed in a harsh winter.
