We just had a lilac planted and mulched mid-Spring. It has been stressed since then and we just noticed in mid-July some frass underneath at the base of the shrub. We took a photo underneath and there's a small space under the bark. Is there any treatment for a potential borer at this time of year?
We viewed your photo. The lilac does not look good and there is no chemical control. If you have a guarantee, we recommend replacement. https://extension.umd.edu/hgic/borers-shrubs