Boxwood leaves turning white at tips - Ask Extension
I recently sprayed my boxwoods with neem oil for leaf miners (visible damage on leaves). About 1 week later there are a few leaves randomly on each pl...
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Boxwood leaves turning white at tips #861683
Asked March 16, 2024, 3:57 PM EDT
I recently sprayed my boxwoods with neem oil for leaf miners (visible damage on leaves). About 1 week later there are a few leaves randomly on each plant turning white at tips with a brown line closer to base of leaf. These are established plants. I did transplant a couple of them, but even the no transplanted boxwoods have a few leaves like this. Thanks in advance.
Clermont County Ohio
Expert Response
Thank you for asking Extension about your boxwoods. From your description, I am not sure the neem oil was effective against the leaf miners at this time of year (although everything is early so far).
Leaf miners that produce visible damage in leaves are the larvae of flies. The flies usually don't emerge as adults until April/May, when they lay their eggs and then die within 24 hours. The larvae will overwinter in the older leaves and pupate usually in April. The adults emerge 3-4 weeks later, when insecticide is most likely to work on them. (Neem oil works by suffocating the insect it is applied to.) The leaf miner damage is visible on the underside of the leaf as the larva feeds between the inner and outer surfaces of the leaves in late summer to early fall.
This is an article about leafminer damage to boxwoods in Ohio with good illustrations
https://bygl.osu.edu/node/2102
Neem oil can affect non-target insects, and should be used cautiously and with close attention to label instructions. It can cause "burning" on the leaves, especially if applied on a warm, sunny day (exactly the types of days we like to get out in the garden).
There are other diseases that can cause damage to boxwoods, a fungal disease known as "boxwood blight" being among them. If you are unsure of the exact cause of the damage you saw, submitting a sample to the C. Wayne Ellett Plant and Pest Diagnostic Clinic would be a great idea. While leafminers may indeed have damaged the affected leaves, there may have been another cause that needs a different treatment. The link to the website is immediately below.
https://ppdc.osu.edu/
The following two websites discuss leafminer damage in boxwoods with illustrations:
https://extension.psu.edu/the-boxwood-leafminer-makes-its-yearly-entrance-in-spring
https://extension.umd.edu/resource/boxwood-identify-and-manage-common-problems/
And this one mentions some of the drawbacks of using neem oil.
https://extension.unh.edu/blog/2020/01/what-should-neem-be-used-plants
This is an article about boxwood blight in the Cincinnati area in 2019. I don't know that this is your immediate problem, but it is something to watch for.
https://bygl.osu.edu/node/1359
Anyhow, the brown tips on the leaves have been killed by something whether it was neem oil "burn" or damage from the insects pupating and leaving the leaves. If the damaged leaves do not make up a majority of the plant, pruning the unsightly branches may be sufficient. Submitting samples to the C. Wayne Ellett Clinic (as above) would help you know whether or not you have something more serious going on.
Leaf miners that produce visible damage in leaves are the larvae of flies. The flies usually don't emerge as adults until April/May, when they lay their eggs and then die within 24 hours. The larvae will overwinter in the older leaves and pupate usually in April. The adults emerge 3-4 weeks later, when insecticide is most likely to work on them. (Neem oil works by suffocating the insect it is applied to.) The leaf miner damage is visible on the underside of the leaf as the larva feeds between the inner and outer surfaces of the leaves in late summer to early fall.
This is an article about leafminer damage to boxwoods in Ohio with good illustrations
https://bygl.osu.edu/node/2102
Neem oil can affect non-target insects, and should be used cautiously and with close attention to label instructions. It can cause "burning" on the leaves, especially if applied on a warm, sunny day (exactly the types of days we like to get out in the garden).
There are other diseases that can cause damage to boxwoods, a fungal disease known as "boxwood blight" being among them. If you are unsure of the exact cause of the damage you saw, submitting a sample to the C. Wayne Ellett Plant and Pest Diagnostic Clinic would be a great idea. While leafminers may indeed have damaged the affected leaves, there may have been another cause that needs a different treatment. The link to the website is immediately below.
https://ppdc.osu.edu/
The following two websites discuss leafminer damage in boxwoods with illustrations:
https://extension.psu.edu/the-boxwood-leafminer-makes-its-yearly-entrance-in-spring
https://extension.umd.edu/resource/boxwood-identify-and-manage-common-problems/
And this one mentions some of the drawbacks of using neem oil.
https://extension.unh.edu/blog/2020/01/what-should-neem-be-used-plants
This is an article about boxwood blight in the Cincinnati area in 2019. I don't know that this is your immediate problem, but it is something to watch for.
https://bygl.osu.edu/node/1359
Anyhow, the brown tips on the leaves have been killed by something whether it was neem oil "burn" or damage from the insects pupating and leaving the leaves. If the damaged leaves do not make up a majority of the plant, pruning the unsightly branches may be sufficient. Submitting samples to the C. Wayne Ellett Clinic (as above) would help you know whether or not you have something more serious going on.
Thank you very much for the informative response!
You're very welcome. Hope the boxwoods look better shortly.
