Dying Marionberries - dark blotches with white blob

Asked August 24, 2020, 6:17 PM EDT

Hi,

I just lost two big, healthy Marionberry canes within a week of one another. There's still some healthy growth at the bottom, but farther along the cane the leaves have all withered and the canes have dark blotches, most of which have a small, white blob on or near them (see picture.) I'm assuming some sort pest or fungus, but I'm hoping someone can be more specific.

Lane County Oregon

1 Response

There are probably a couple things going on here. The reddish lesions are probably a common fungal disease called Purple Blotch - here is some information - http://whatcom.wsu.edu/ipm/manual/black/purple_blotch.html

However, the Purple Blotch alone probably would not cause the canes above the lesions to wilt & die. There is a possibility that this could be the result of the Rose Stem Girdler, a small coppery, metallic beetle that is becoming more common in the Willamette Valley. It normally lays eggs on the bottom third of a cane. Then larvae bore directly into the cane, resulting in wilting above this area in mid-summer. Recommend that you cut the effected canes just below the wilted portion and keep cutting to see if any larvae/other pest is present.
Here is information on these beetles - https://pnwhandbooks.org/insect/small-fruit/blackberry-raspberry/blackberry-raspberry-rose-stem-girdler

Then, it is strongly recommended that you remove and burn (or dispose in the garbage) any effected canes. This may help reduce future populations.