Master Gardener Sue Morris: Lilac problems also seen in west central Minnesota
Lilac dieback, browning of leaves, is now seen locally,
Earlier this year I wrote how there had been reports from other parts of the state about lilac dieback, browning of leaves, etc. I had not had any reports of that locally.
Since that time, when driving around the county, I have noticed that there is a lilac problem here as well. I have noticed lilac hedges that were bare. Others that have brown and/or dying leaves.
So I would like to delve into the lilac issue a bit further and pass along good information from the University and what, if anything, can be done to remedy the problem.
The common lilac is reportedly the most affected species. It is unknown whether specific cultivars are affected more than others because most people don't know the cultivar. Affected plants are reportedly mature and have never been a problem before this year.
Leaves turn yellow, then brown, then drop. Branch dieback is random, on one shrub in the middle of a hedge, all one side of a hedge or on individual branches. The University believes the weather this year had a lot to do with this problem.
There was an early cold snap with no snow cover so roots weren't protected; July was the 14th warmest and 14th wettest since 1895; day temps were in the 90s, nights in the 70s and dew points over 70 degrees F. Conditions like these can stress plants and slow down development and volatilize herbicides.
If herbicide was applied during times of high heat and humidity, broadleaf weed treatments on lawns can volatilize, turning to a gas and drift onto non-targeted plants. Cupping and browning are symptoms of this: along one side of hedge and not the other; at same level across a base of shrubs planted in or near lawn areas, especially downwind from prevailing winds.
What can we do to prevent this from happening again? Clean up fallen leaves to reduce the likelihood of reinfection next season. Renewal prune to decrease density and consistent watering will help support the stressed plant. Keep an eye on the plant in 2021 for signs of permanent damage and the possibility the plant may need to be replaced.
If you decide to replace the lilac(s), there are many great plants including resistant lilacs that could be good replacements. Perhaps the lilac is at the end of its life. Lilacs are relatively long-lived plants (25 to 50-plus years) depending on how they have been cared for and their growing conditions.
If the affected lilac(s) are of great value to you, you may want a certified arborist to assess the plant. Has this problem occurred repeatedly for multiple years? Have management methods failed in the past?
Some of this information is a repeat from the earlier column but since there is so much local damage, I felt it was important to talk about prevention.
(Information taken from Julie Weisenhorn, Extension horticulture educator)