Have you noticed branches dying on Honeylocust this summer? We’ve had reports of branch dieback on urban street trees in the Hamilton and London areas last month.
We saw several trees with branches exhibiting yellowing and browning foliage at various locations in the canopy.
A closer examination of the bark at the base of the symptomatic twig showed bark discolouration, lifting and desiccation.
But we could not find any distinct signs of cankers or any consistent signs of insect activity. The bark symptoms almost reminded me of sunscald on thin barked juvenile trees which we see in nursery production sometimes.
We dissected several symptomatic branches and found that indeed, the sapwood had been partially killed. We sent several samples to the Pest Diagnostic Clinic in Guelph. The lab found a pathogen association with a small percentage of the symptomatic twigs. That pathogen is Botryosphaeria sp. But in our opinion, winter damage was the real primary cause of the branch dieback, and the pathogen was a secondary organism taking advantage of the recently killed sapwood. Botryosphaeria is a saprobe, it can live and reproduct on dead tissue.
Prune out symptomatic branches on Honeylocust and destroy/chip those branches as soon as possible.