ASK YOUR SCIENCE TEACHER | Local News - WisconsinFan.com

ASK YOUR SCIENCE TEACHER | Local News

QUESTION: Why are my lilacs dying, and yet some are now blooming as we go into October?

ANSWER: Yes, the Scheckel lilacs have been dying all summer, starting with the lower branches and leaves and working its way up the plant. It’s happening all over our area this summer, and it’s a shame as the lilac is the most beautiful and fragrant of all the flowering shrubs. There are few things that smell better than lilacs in full bloom. Some lilacs in our backyard have blooms on them, but they don’t seem to be as fragrant as the spring lilac flowers.

The evildoer is Septoria leaf spot, a fungus related to the Septoria leaf spot that ravishes tomatoes. The accomplice is the many rains and wet conditions we’ve had this summer. The bountiful and timely rains produced excellent corn and soybean crops, but Septoria thrives in wet conditions. Many days of very hot weather encourages Septoria, and we’ve had those days this summer.

Septoria is first noticed with the browning of the leaves at the bottom of the plant and gradually working upward. The leaves blacken and fall off, leaving the bottom of the lilac shrub bare. It looks like the plant is dying. Experts say not to worry as the lilac will survive and Septoria will be gone next year if we have drier weather. We can expect fewer lilac blooms next spring.

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Lilacs will bloom in the fall if the plant undergoes some type of stress. Drought and wind damage can also trigger blooming. It’s as if the lilac is saying to us, “Look at me, I’m not dying, I can still produce blooms.” Lilacs will go dormant during the summer because of drought. Later in the summer, they revive and bloom when the rains come. It happened around Monroe County in 1988.

Reassurance of life in the lilac can be seen by examining the branches and finding healthy leaf buds. Next year will produce a healthy lilac tree, but the blooms may be fewer. It is recommended raking up the dead leaves and either burn them, bury them, or put them in a compost. It’s also recommended that the lilac bush be pruned to thin out the canopy of growth to promote more rapid drying of the leaves.

If Septoria hits us again next summer, it is possible to spray the lilacs with a fungicide. A fungicide will also hit another lilac headache, powdery mildew. Powdery mildew, as the name implies, produces a white, powdery growth on the leaves. Powdery mildew is not fatal but makes the tree look sick.

The lilac was one of the first plants brought over to America by colonists, arriving in the 1750s. Both George Washington and Thomas Jefferson grew lilac shrubs in their gardens. Lilacs became common in many botanical gardens. Poet Walt Whitman elevated the lilac to cult status with his poem, When Lilacs Last in the Dooryard Bloom’d. Whitman penned the long poem in the summer of 1865 as a tribute to President Abraham Lincoln and during a profound national mourning of the president’s assassination on April 15. Lilacs live to be about 100 years old. The lilac is the state flower of New Hampshire.

Sources: Wikipedia, University of Wisconsin Extension, Facebook post.

Larry Scheckel is a retired Tomah High School physics teacher.

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