The boxwood starts out by browning at the bottom and working up the sides.

Hi Miriam,

I am so sorry to hear about your boxwood leafminer issues. If company in misery helps, please know you are not alone. This has been a problem throughout Ohio this year. I am providing several links to help you understand the issue and possible solutions. Each of the articles discusses various issues with leafminers and possible management plans. Some experts recommend using insecticides though others believe it is difficult to get the timing right (see second link). If you decide to use an insecticide, please follow the instructions carefully. Here is a quote from the first link on the use of insectides:

“… insecticide applications remain an option to manage boxwood leafminer on older more susceptible boxwoods. This is particularly important if the boxwoods cannot be easily replaced owing to their size and importance in landscape designs.

Timing is critical for both foliar and systemic applications. While foliar applications made at the time adult leafminers are flying can be effective, the downside is that non-target arthropods may be killed including predaceous insects and mites as well as spiders.

The Virginia Tech publication, “Horticulture and Forest Crops, 2023 Pest Management Guide” (see Additional Resources below), lists the systemic insecticides dinotefuran (e.g., Safari, Transtect, etc.), imidacloprid (e.g., Merit, Xytect, etc.), and cyromazine (Citation) as being effective against boxwood leafminer larvae. Dinotefuran and imidacloprid are neonicotinoids and cyromazine is an aminotriazine insect growth regulator (IGR).

Systemics reduce the risk to non-targets; however, they are not risk-free. Neonicotinoids may be found in flower nectar meaning that applications should be made after flowering to reduce the possible indirect risk to pollinators.”

I encourage you to read through the first article as it outlines other potential issues that may not be leafminer. 

https://bygl.osu.edu/node/2102

https://www.canr.msu.edu/news/boxwood_leafminer_a_serious_pest_of_a_favorite_landscape_plant

https://extension.psu.edu/boxwood-leafminer

https://boxwoodsociety.org/abs_care.html

Hopefully, this information will help you with your boxwoods.

Just wanted to provide my signature, Miriam.