Apple tree pest or virus?

Asked December 23, 2018, 2:16 PM EST

I have 4 espaliered apple trees (3-4 yrs old). Recently, I noticed these marks that first looked like burn marks. Upon further inspection, I see that the bark is being eaten away and perhaps there is some type of borer pest. It is at the grafted joints. What can I do to prevent further damage and save my trees?

Multnomah County Oregon

3 Responses

These trees will not do well in the long run. I'll try to explain what I see in the images and what you might be able to do.
It kind of looks like the middle scaffold branch was susceptible to something as 2 of the images seem show similar damage. I can see that the canker (the dead areas) extend down into the root stock portion. I am looking at the discoloration and flattening of the trunk below the damaged area. It also looks like the damage has been there for 1 to 2 years based on the growth of the wood at the margin of the canker - the tree is trying to seal off that area.
I am not sure what the primary problem was but the damage has let other fungi in and this will continue to rot the heart wood. The trees will limp along for another few years but will continue to decline.
The primary fungus could have been what we call anthracnose canker but you would have to send in damaged tissue for analysis to be sure. There are several other fungi that can look like this. In any case there is nothing short of a saw that will get rid of the infection. You can learn more about this disease here:

Hi Jay,
I read about the bullseye rot and looked at additional pictures online. I am not sure if this is the issue. I am seeing evidence of what I believe to be a pest - possibly a borer as there are holes inside the cankers and sawdust left behind. This also is very new as I pruned last year and tied every branch down to wire and never noticed one injury or damage. This seems very sudden and significant. It looks like burn and then further damage.

I found this site that discussed weakening of plants due to sunburn and I believe that could be very possible. The berries I have in the same sun direction experience sunburn and I was thinking of how to protect them this next season. A couple of the pictures look very similar. This post is from a desert area, but as we are experiencing more drought and higher temps each summer, do you think this pest is a possibility? The flat head apple tree borer or the Pacific flat head borer. If so, how can I treat in these winter, rainy months?
Thank you for your time.

Yes, you could have sunburn, especially if the damage on each tree is on the south or southwest side. The primary problem was sunburn, the secondary problem then are the pest that are opportunistic and get into the tree through the wounded area. Many insects (as you are suggesting) and fungi can do this.
There is not a lot you can do for the damaged portions of the tree. Sunburn can be prevented by watering during hot summers and using a white latex paint on the trunks and large limbs prior to winter. Covers or wraps will do the same, you just want to reflect the sun's energy away from the tree. Keeping the damaged area dry is the best you can do. I would not use any pesticides at this point.