Korean Lilac – Is it showing disease?

Asked September 27, 2020, 8:47 PM EDT

I planted a young Korean Lilac bush this summer in the Annapolis area. (If not familiar with it – it was developed in Korea by a U.S. serviceman and named after his assistant. Given similar environments to Maryland – hot summers and cold winters, I am hoping it does well. Expected to only grow only 4-5’ height and produce fragrant lavender blue flowers.) I am attaching a few photos wondering if it is becoming diseased. What might be causing the top leaves to curl and go brown? (For example – too much water or too little? I essentially watered this plant daily through the summer …tag suggest not to let the root ball become dry during its 1st season.) Also, I am just noticing that the stems of this bush have a pattern of white dots or bumps running along the stems – I do not know if this is natural or an indication of a problem. If a problem please advise how I might arrest the situation. Sincerely, George from Crownsville

Anne Arundel County Maryland

1 Response

We have seen multiple examples of very stressed lilacs this year -- leaf spots, browning, and early defoliation. Yes, water deficiency could be an issue if it has been very dry in your area and especially if it is a newly planted lilac that has not been watered regularly to help it establish the root system. Plants will shed leaves early that are either too damaged to function well or for which the plant does not have enough moisture to retain.

Late spring frosts this year damaged tender leaf tissues that had already broken dormancy, facilitating infection from bacterial leaf pathogens. These diseases don't always cause symptoms of infection until later in the season, when summer heat stress worsens for the plant. (https://extension.umd.edu/hgic/topics/bacterial-blights-lilac)

Powdery mildew is relatively common on lilacs and can cause leaf damage beyond just a white/gray coating on the leaves; the damaged leaf portions can "burn" and crisp after summer heat and drought stress them.

These are some possibilities for the browning and curling you are seeing.

Now - Make sure mulch is no thicker than several inches and away from the base of the stems. Monitor your plant for watering needs during the autumn months, soaking well but only as needed when the top several inches of the soil has dried somewhat. Daily watering may be too much. Move the mulch aside and check the soil moisture by probing with a screwdriver about 6 inches deep and check with your finger. Soil should be damp to the touch. Let the soil dry before watering again. Refer to our guidelines on watering https://extension.umd.edu/hgic/topics/watering-trees-and-shrubs

We have had autumn droughts in the past - just last year in fact - so continuing to monitor your plant's moisture until the frosts arrive would be beneficial.

The white bumps on the stems are called lenticels. They serve as "breathing holes", allowing oxygen to enter the living cells of the bark tissue and this is normal. They maybe more noticeable on some trees/shrubs than others.