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Lilac Blight in Iowa

lilac bush in bloom

Lilacs are a favorite spring shrub in Iowa. They are especially loved for their sweet fragrance and their cone-shaped panicles covered with tiny blooms. However, over the last several years, lilacs have been showing signs of significant stress and lack of vigor. The culprit: lilac blight. The first signs of lilac blight are almost impossible to notice with the naked eye, but before long it becomes obvious that our beloved lilacs are struggling.

What Is It?

Lilac blight is a potentially serious lilac disease caused by bacteria that infect the plant in early spring when the weather is cool and moist. Lilac bacterial blight is caused by the bacterium pseudomonas syringae pv. syringae. A natural opening or wound is required to cause infection, but the disease can be spread by the wind, splashing rain and pruning tools.

Lilac blight has always been present in Iowa.  However, over the last several years, conditions have been more favorable for the disease, giving it the opportunity to really spread and progress. We are seeing widespread damage to lilacs in Iowa and across the Midwest. Plants are experiencing significant stress and dieback, like seen in the tree below.

Lilac blight affects old lilac shrub leaving large areas of dead branches behind

How To Recognize Lilac Blight

In its early stages, lilac blight is almost impossible to see without the help of a microscope or sending samples to be tested in a lab. Even once signs of the disease start appearing, it can be hard to know what is affecting the plant as these symptoms are common with many diseases.

Early signs of lilac blight are small brown spots or deformed leaves. When new shoots are affected it can be obvious as the branch turns black, wilts and eventually dies, while old, woody shoots on the other hand will often stay upright.

As the season and disease progress, you will notice brown edges and streaking in the leaves. Those small brown spots will grow and merge together, eventually taking over the whole leaf. Then you will see early leaf loss. 

You may even see your lilac has new growth and is trying to rebloom midsummer. This is a sign that the plant is under severe stress and is a main symptom of lilac bacterial blight. 

Two images showing lilac leaves infected with lilac blight. Left: Early stages of lilac blight with only a few small brown spots. Right: brown spots take over larger areas of a lilac leaf. Affected areas show crispy edges and the leaf has become misshapen.

What To Do

There are some options available to treat lilac blight, but treatment can prove difficult. The best option is to seek out lilac varieties that are resistant, like Miss Kim and Dwarf Korean Lilacs.

If you already have affected or susceptible lilacs in your landscape, copper fungicide can be sprayed on buds just as they break early in the season before leaves have reached full size. Any branches that have died back or are noticeably diseased should be removed and destroyed.

Lilac blight can overwinter in fallen leaves, weeds and soil. For this reason, it is beneficial to rake away any plant debris from your lilac. 

Another very important tip is to make sure your pruners are cleaned between each cut, even if there is no sign of infection. A common way for any bacterial disease to spread through the garden is contaminated pruners. Dip your snips in a solution of 10% bleach each time you prune a branch. You should also only prune when the weather is dry and there are no chances for rain in the coming days.

Left: Miss Kim Lilac blooms Right: Dwarf Korean Lilac blooms

Lilac blight isn’t anything new and isn’t going anywhere any time soon. Treatment can be difficult, so save yourself the stress and shop disease resistant varieties available at Ted Lare Garden Center


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