do we need to have lilac trees sprayed for leaf spot forever? - Ask Extension
For years, our Japanese lilac trees developed brown spots early in the season every year, then dropped their leaves in August.
In 2018, they were dia...
Knowledgebase
do we need to have lilac trees sprayed for leaf spot forever? #870904
Asked May 31, 2024, 9:45 AM EDT
For years, our Japanese lilac trees developed brown spots early in the season every year, then dropped their leaves in August.
In 2018, they were diagnosed, I believe by CFANS, but of course I don't remember the correct name of the diagnosis.
Bartlet has been spraying them preventively for "leaf spot fungus" 4 times a season for 5 years, with excellent (but expensive) results.
(They also do a 1 time per summer "prescription soil treatment" which I declined this year.)
*** Does the spraying need to be continued indefinitely 4 times per season?
*** Also, do they bloom on some type of cycle? This year is the second time in 13 years that there are just a few blooms on our most mature trees; the smaller ones have many buds,
Dakota County Minnesota
Expert Response
Without knowing the disease you are treating for, I can only make a couple of guesses. Lilacs (though tree lilacs less so) are all susceptible to powdery mildew, but this does not affect the health of the tree and I wouldn't be treating for it. Pseudocercospora leaf spot is less likely and also doesn't usually require treatment:
https://yardandgarden.extension.iastate.edu/encyclopedia/lilac-pseudocercospora-leaf-spot
However, it might need treatment for bad infestations.
My suggestion is to stop treatments for one or two seasons and follow a careful sanitation strategy:
https://extension.umn.edu/plant-diseases/leaf-spot-diseases-trees-and-shrubs
If the disease returns, then restart treatments the following season.
https://yardandgarden.extension.iastate.edu/encyclopedia/lilac-pseudocercospora-leaf-spot
However, it might need treatment for bad infestations.
My suggestion is to stop treatments for one or two seasons and follow a careful sanitation strategy:
https://extension.umn.edu/plant-diseases/leaf-spot-diseases-trees-and-shrubs
If the disease returns, then restart treatments the following season.
Sorry, I didn't answer your last question. I am not aware of any bloom cycle for tree lilacs. Reduced bloom can have many causes, including improper pruning, lack of sun, weather, too much nitrogen fertilizer, and so forth:
https://www.chicagobotanic.org/plantinfo/lack_flowers_lilacs
https://www.chicagobotanic.org/plantinfo/lack_flowers_lilacs
Dennis,
Thank you!
Kathy Haug
Sent from my iPhone
On May 31, 2024, at 3:49 PM, Ask Extension <<personal data hidden>> wrote:
Dennis,
Sent from my iPhone
I took your advice and cancelled service after the first spraying in May.
Now our Japanese lilacs are again dropping leaves 2 months early.
Where can I send a leaf sample to re-diagnose?
Thank you,
Kathy Haug
Sent from my iPhone
On May 31, 2024, at 5:06 PM, Kathy Haug <<personal data hidden>> wrote:
Dennis,Thank you!Kathy Haug
Instructions on submitting a sample here:
https://pdc.umn.edu/submit-sample
https://pdc.umn.edu/submit-sample
