U.P. Michigan blueberry stem issues

Asked June 6, 2018, 11:48 AM EDT

It's been a long, cool and somewhat wet spring here in the U.P. and a local resident brought blueberry stems to our office looking for a diagnosis and information regarding the best way to combat whatever is affecting their blueberries. Plants started looking "funny" last year but are much worse this year. Botryosphaeria Stem Canker or Phomopsis Twig Blight are about the best I could come up with but don't want to misdiagnose so your assistance would be greatly appreciated.

Houghton County Michigan

1 Response

It is not Botryoshaeria which is really a southern disease.
It is not phomopsis which would kill the stem and cause the shoot to die. Phomopsis is pretty common in Southern Michigan but we seldom see it in northern Michigan or the UP. Fusicoccum is the most common northern stem blight and it is not it either.
I get asked this question a lot and I think it is the normal stem transition as the epidermis of the young stem is replaced by periderm as the bark begins to form as the stem ages. Eventually the stems will turn red, orange, yellow or purple as the stem ages and then be covered with gray bark as the periderm dies.
It seems more pronounced and appears a speckling on bushes of low vigor that are not pruned or fertilized. It seems worrisome to small and back yard growers who think the bush has a disease but really they need a little more vigor. There is also some sooty blotch, the black fungus, growing on the green shoots. It is just growing on the waxy cuticle of the stem and not causing any harm it also grows on raspberry, blackberry stems.
I would guess the plants are shaded and not growing well.
Call me if you want