Can you help confirm if I have boxwood blight? The two pictures are from two separate hedges. If it is, can I spray now? I also would like a confirmation so I can report it to Landscape Ontario. I am in south Etobicoke. Thank you.
Dear Boxwood Owner,
Thank you for writing, and for the close-up of your Boxwood plant, that indeed appears to be having a tough time of it with blight. Please see here our Toronto Master Gardener’s informative advice on the subject of Boxwood blight, caused by the fungus Calonectria pseudonaviculata, commonly referred to as Buxus blight.
For further reading, particularly on the prevention of blight, and plant management, please see this tract published by Perdue Extension Research.
We’re also looking closely at your photo for any signs of fine web material, or droppings, of the box tree moth larvae. The BTM is an invasive pest also capable of causing severe damage — leaves are ‘skeletonized’ by the chewing larvae — to plants in Ontario, and particularly during seasons following mild winters, resulting in high levels of eggs hatching. If this was the case, yes, boxwood leaves could be sprayed mid-May (and again, when the next set of eggs hatch, in the summer), with a biological insecticide containing a naturally occurring bacterium, Bacillus thuringiensis (B.t.), which causes the caterpillars to become ill after feeding on sprayed foliage.
But as Buxus blight is a fungus, not a BTM pest, there is no ‘spray’ product to apply. If you contact Landscape Ontario, you will likely be able to locate a professional, for an in-person consultation re management options going forward.