Hi All, Happy Holidays!
I’m new to Apple growing (3 Cummins trees, Liberty, Freedom, Williams’ Pride, all in 3rd year on semi-dwarf rootstock), so apologies if this is a basic question. As I was getting the trees ready for winter I noticed something odd at the base of one of them. See pictures below. It’s a bulge in the trunk near the original graft union. I was thinking maybe crown gall, but it doesn’t really look like other pictures I can find of crown gall. It normally has a white spiral-wrap trunk guard around it, which I moved up for the picture. Am I looking at a burr knot here? It does have some roots growing off of it, but is pretty smooth in parts as well.
Looks like a burr knot to me. Also, your landscape fabric or whatever that is too close to the trunk.
What exactly is the rootstock? MM111 makes burr knots a lot.
Thanks! It’s on a G890 rootstock. It is landscape fabric loosely wrapped around the base. What issues will having the fabric that close cause?
I don’t think it is wrapped loose enough. You should get that fabric (and any other mulch at least a few more inches away from the trunk.
I had growths like that on quite a few of my apple trees that I kept the white spiral plastic on for over a year. Sort of looked like knobby knees. After discussing with others, I removed the plastic and filed down some of the growth earlier in the summer. I ended up whitewashing the trunks instead. It happened in all 5 trees that were wrapped, so Im sure that is the common denominator.
Thanks for the advice! I was wondering if the spiral-bound wrap was problematic because it does have sharp edges. This gives me an excuse to whitewash.
@ribs1 I’ll back the landscape fabric off all 3 trees. I haven’t mulched there, only had the fabric with stone over it. Do you suggest keeping the stone away as well? In spring I’ve been pulling the fabric/stone away to spread compost around the base (away from trunk), then re-laying the fabric/stone.
I have the same problem on a couple of the trees that I have used spiral wrap on. I very likely left it on too long. Last two trees that spiral wrap was not used on, do not have that problem. Most are on G11.
I’ve had some grafts on M-111 do the same. No spiral wraps or fabric close to the base or anything of that sort either.
This site suggests high humidity and temp may favor burr (What's the Difference Between Tree Burr Knots (Burl) and Crown Galls?)
Apparently, there is quite a market for burr knots due to their unusual markings when developed into wood worker crafts like bowls.
I have seen the burr knots on some of my trees as well. I will have to re-examine what rootstocks seem affected, I used the white spiral guards on them and the vast majority of my trees no not have the burr knot issue. So I would have to question the part about the white spiral guards being an issue. At least at my location. I would also think the issue may be with certain apple varieties.
I just found this from PSU extension regarding G.890:
“Tree does produce rootsuckers but we have not seen any evidence of burr knot formation.”
So what I’m seeing may be natural for the rootstock.
@MikeC, I may be totally wrong, but history leads me in that direction. Some of the burr knots even have a twist to them that could be the result of a spiral cover. Maybe it is the rootstock, unsure?
True, I am not sure if the spiral covers make a difference. If they did I would think all my apple trees would have them since I used them on all of mine. I will take an inventory here in the spring to see what is and is not affected with burr knot. There are not too many I have that have gotten burr knot. Plus did I plant them too deep, not deep enough, etc…